MiniReview

Current status of pathogenetic mechanisms instaphylococcal arthritis

Andrej Tarkowski �, Maria Bokarewa, L. Vincent Collins, Inger Gjertsson,Olof H. Hultgren, Tao Jin, Ing-Marie Jonsson, Elisabet Josefsson, Egidija Sakiniene,

Margareta VerdrenghDepartment of Rheumatology and In£ammation Research, University of Go«teborg, Guldhedsgatan 10, 413 46 Go«teborg, Sweden

Received 13 September 2002; received in revised form 18 October 2002; accepted 18 October 2002

First published online 14 November 2002

Abstract

Interactions between staphylococci and the joint tissues of the host lead typically to rapidly progressing and highly destructiveprocesses. Staphylococci possess a vast arsenal of components and products that contribute to the pathogenesis of joint infection.Occasionally these compounds have overlapping activities and act either in concert or alone. Host responsiveness to staphylococcalinfection displays an even more complex pattern. Most of the cells and molecules that participate in the innate immune system protect thehost against bacteria. However, the staphylococci have developed systems that counteract endogenous protective mechanisms.Interestingly, certain cells and molecules of the acquired immune system potentiate the severity of infection by triggering exaggeratedresponses to the staphylococcal danger signals. This review deals with the intricate host^bacterium interactions that occur duringexperimental septic arthritis, and outlines potential preventive and treatment modalities.6 2002 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.

Keywords: Staphylococcal arthritis ; Pathogenetic mechanism; Host-bacterium interaction

1. Introduction

The genus Staphylococcus includes more than 30 species,only three of which are of major clinical signi¢cance: S.aureus, S. epidermidis, and S. saprophyticus. The clear ma-jority of all bacterial isolates, in cases of joint infections ofnon-prosthetic origin, involve S. aureus. This type of in-fection is almost always hematogenously spread, resultingin a high proportion of cases in severe and irreversiblejoint destruction, and occasionally in mortality. Impor-tantly, both these outcomes may arise in spite of adequateantibiotic therapy which indicates that the in£ammatorycascade initiated by the staphylococci and leading to jointdestruction and mortality persists even in the absence oflive microorganisms. This fact, together with the emer-gence of highly antibiotic-resistant strains, underlies theurgency of e¡orts to better understand disease pathogen-esis and in particular the crucial bacterium^host interface.

In order to study the details of the host^bacterium inter-action, one needs to use adequate animal models, not leastso as to be able to study the initial phases of the infectionand to assess novel prophylactic and treatment modalities.We have recently reviewed the current state of modellingof staphylococcal infections in general [1], and of S. aureusarthritis [2]. The aim of the present review is to discuss insome detail our ¢ndings regarding host^bacterium rela-tionship that were obtained using this model, and to putthese results in the context of recent advances in anti-staphylococcal therapies.

2. Why do the staphylococci persist in the joints?

Circulating S. aureus, if present in signi¢cant numbers,will invariably extravasate into most if not all of theparenchymatous organs of the experimental host (themouse). However, within a few days to 1 week the innatesystem of the host typically clears the infection from mostof the organs, with two major exceptions: the kidneys andthe joints. Whereas chronic infection of the kidneys with

0378-1097 / 02 / $22.00 6 2002 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.PII: S 0 3 7 8 - 1 0 9 7 ( 0 2 ) 0 1 0 9 2 - 3

* Corresponding author.E-mail address: andrej.tarkowski@microbio.gu.se (A. Tarkowski).

FEMSLE 10747 28-11-02

FEMS Microbiology Letters 217 (2002) 125^132

www.fems-microbiology.org

S. aureus does not lead to severe kidney failure, infectionof the joints ultimately leads to a total or subtotal destruc-tion of the cartilage and subchondral bone [3].What are the mechanisms leading to this long-lasting

persistence of staphylococci in the joint cavity? One verypeculiar characteristic of the joint cavity is its avasculararea, i.e. the hyaline cartilage. Since this area represents alarge fraction of the overall surface area of the joint cav-ity, the extravasation of cells and plasma proteins belong-ing to the immune system may be delayed and quantita-tively low. Indeed, we have found that the induction ofmRNA for in£ammatory cytokines and chemokines inresponse to hematogenous infection with S. aureus wasfaster in the spleens than in the joints of the same subject[4]. Another factor of major importance for the regulationof S. aureus persistence in the joints is tissue tropism.Tissue tropism for staphylococci is regulated by a numberof adhesins whose ligands are expressed densely in jointtissues. The adhesin^ligand interaction retains the bacteriain the joint by delaying the elimination of microorganismsby the immune system. We have recently shown that col-lagen adhesins, bone sialoprotein adhesins, protein A,which interacts with host IgG, as well as ¢brinogen adhe-sins, expressed by S. aureus, are all virulence mechanismsoperating in septic arthritis [5^7]. Indeed, virulent staph-ylococcal strains that are capable of causing severe septicarthritis and mortality become highly attenuated upon se-lective inactivation of adhesin genes [5,6]

3. Bacterial virulence factors

Using modern genetic approaches, it is relatively easy toassess the pathogenic role of a given molecule produced bya bacterium. Indeed, site-directed mutations can selectivelysilence a single gene without a¡ecting the remainder of thegenome. Using this technology, one can successfully studythe relative impact of speci¢c genes on virulence in vivo.As already stated above, certain adhesins display im-

portant virulence-related properties. These adhesins aretightly regulated by genetic regulatory elements (e.g. theagr and sar loci) and by sortase. Both types of regulationhave obvious consequences for the outcome of S. aureusarthritis. Indeed, inactivation of the agr/sar (Fig. 1) orsortase A (Fig. 2) loci leads to clear-cut amelioration ofseptic arthritis [8,9].Other constituents of the bacterial cell wall, which in-

clude the polysaccharide microcapsule and peptidoglycanare also potent regulators of virulence. Indeed, staphylo-cocci that are defective with respect to the expression ofthe type 5 capsular polysaccharide induced a lower fre-quency and severity of arthritis in murine recipients thanthe congeneic wild-type strain. Further in vitro studiessuggested that this outcome was due to the enhancedphagocytosis and intracellular killing of bacteria thatlacked capsular polysaccharides [10]. Recently, we have

shown that staphylococcal peptidoglycans are potently in-£ammatogenic: a single intra-articular injection triggeredsevere and long-lasting arthritis with occasional signs ofcartilage and bone destruction [11].Furthermore, molecules secreted in vivo by staphylococ-

ci may by themselves or in concert with other factors leadto severe joint damage and increase the risk of infection-related mortality. This is true for enterotoxins and TSST-1as well as exotoxins. In the case of TSST-1 and the enter-otoxins, we have shown that their superantigenic activitiesaccelerate and worsen the outcome of sepsis and septicarthritis [12,13]. Such a deleterious outcome is due to theactivation of certain CD4þT cell subsets (see below) whichsubsequently lead to exaggerated cytokine responses. Thepathogenicity of exotoxins is somewhat more complex. In-deed, each exotoxin per se does not increase signi¢cantlythe severity of septic arthritis. In contrast, staphylococcithat have simultaneous expression of alpha and gammatoxins give a signi¢cantly worse outcome for septic arthri-tis [14].Certain components of bacteria cannot be tested for

their virulence properties within living microorganisms be-cause deleting these components would render the bacterianon-viable. A good example of this is the bacterial genomeitself. Extracted and highly puri¢ed staphylococcal DNAinduces in£ammation upon local administration. Thus, incase of intra-articular administration, one sees arthritis[15,16,17], whereas intracerebral administration gives riseto aseptic meningitis [18]. The phlogistic properties of bac-terial DNA are due to its structural properties, which in-clude a lack of methylation on the cytosines and a relativeabundance (compared with eukaryotic DNA) of CpG se-quences [15].

4. Bacterial evasion mechanisms

Small colony variants (SCVs) of S. aureus have beenimplicated in persistent and recurrent infections in osteo-myelitis, septic arthritis and cystic ¢brosis. These SCVsdisplay increased resistance to aminoglycosides and cell-wall-active antibiotics and are able to persist intracellular-ly within the host for prolonged periods. We have assessedif this evasion mechanism is of importance for bacterialvirulence in septic arthritis. Our results suggest that thismay indeed be the case. Thus, mice infected with hemBmutants that expressed the SCV phenotype displayedmore severe arthritis than mice inoculated with the wild-type strain. This outcome may be ascribed to the eva-sion mechanism per se and the ability of this mutant toproduce 20 times more protease than the parental strain[19].Antimicrobial host defense peptides, such as defensins,

protegrins, and platelet microbicidal proteins are deployedby the host in response to S. aureus infection. In turn,the staphylococci have developed resistance mechanisms,

FEMSLE 10747 28-11-02

A. Tarkowski et al. / FEMS Microbiology Letters 217 (2002) 125^132126

which are either highly speci¢c for certain host defensepeptides or which broadly protect against a range of cat-ionic antimicrobial peptides. Recently, we have used amodel of septic arthritis to elucidate the roles of two dif-ferent loci, mprF and dltA-D in S. aureus that are crucialto defensin resistance. The DltA-D proteins catalyze theintroduction of D-alanine into the teichoic acids of thestaphylococcal cell wall, whereas MprF is involved inmodi¢cation of the membrane phosphatidylglycerol withL-lysine. The loss of either of these functions has cata-strophic consequences for S. aureus. Thus, the Dlt- mutanthad increased susceptibility to vancomycin and other gly-copeptide antibiotics, was more susceptible to killing bydefensin peptides, and was prone to faster and more e⁄-cient in vitro inactivation by neutrophils [20]. In addition,both the mortality and frequency of arthritis were dramat-ically reduced in mice that were infected with the Dlt-mutant, compared to those that were infected with thewild-type strain [20]. Similarly, the S. aureus strain thatlacked the mprF gene had altered net surface charge,was sensitive to defensin-mediated killing, and was attenu-ated for virulence and arthritogenicity in mice [21].However, even in the presence of the mprF gene the

defensins might with time (within hours) kill the staph-ylococci. The additional line of staphylococcal defenceagainst defensins is their production of staphylokinase.This molecule was believed until recently to participatein the spreading of staphylococci from the vascular com-partment to parenchymatous organs due to its ¢brinolyticproperties. We have recently shown that staphylokinasebeing produced by the majority of staphylococcal strains[22] has the ability to bind human defensins, thereby neu-tralizing their bacteriolytic properties [23].

5. Non-speci¢c innate immune responses to invadingstaphylococci

A cardinal sign of staphylococcal invasion into internalorgans, such as joints, is the acute in£ammatory response,which is characterized by an in£ux of polymorphonuclearleukocytes (PMNs) [3]. This re£ects the major role of theseprofessional phagocytes in ¢rst-line defence against invad-ing bacteria. Indeed, even temporary deletion of neutro-phils leads to an overwhelming systemic infection with avery high mortality rate and severe septic arthritis [24].However, the ability of PMNs to defend the host againststaphylococci is not only dependent on their phagocyticproperties. Indeed, a number of processes lead to (a) intra-cellular killing and (b) extracellular release of moleculesthat are capable of damaging the staphylococci. Uptakeof staphylococci by PMN triggers the so-called respiratory

Fig. 1. Severity of arthritis in mice inoculated with S. aureus strain8325-4, its agr mutant and its hld mutant. Data were analyzed by Wil-coxon signed rank test. P values refer to comparison between the agrmutant and the wild-type strain 8325-4.

0 2 4 6 8 10 12 14

Days after inoculation

100

80

60

40

20

0

Cum

ulat

ive

surv

ival

(%

)

Wild-type strain

Complemented strain

Sortase mutant

p<0.01

A

B

Art

hrit

is I

ndex

(m

edia

n±IQ

R)

0

1

2

3

4

5

6

Sortase mutant

Wild-type strain

Days after inoculation

3 days 7 days 14 days

p=0.04p=0.002

N.S.

Fig. 2. A: Cumulative survival of mice inoculated with S. aureus strainNewman, its isogenic sortase-de¢cient srtA3 mutant, or with sortasemutant complemented with the wild-type sortase gene on a plasmid.P6 0.01 refers to comparison between wild-type Newman and srtA3

mutant inoculated mice. Statistics is calculated using log-rank Kaplan-Meier test. B: Severity of arthritis in mice inoculated with S. aureusstrain Newman or its isogenic srtA3 mutant, not expressing sortase.Data were analyzed by Mann^Whitney U-test. P values refer to com-parison between the sortase mutant and the wild-type strain Newman.N.S., not signi¢cant.

FEMSLE 10747 28-11-02

A. Tarkowski et al. / FEMS Microbiology Letters 217 (2002) 125^132 127

burst and fusion of cytoplasmic granules with the phago-cytic vacuole. Both events lead to noxious environment forthe Staphylococcus. More importantly, the PMN granulescontain bactericidal substances, including myeloperoxi-dase, defensins, bactericidal/permeability-increasing pro-tein, phospholipase A2, cathepsin G, and cathelicidins[1,23,25].Mononuclear phagocytes (i.e. cells from the monocyte/

macrophage lineage) migrate to the site of infection (i.e.the joint) slightly later than the PMN. Their role in septicconditions caused by staphylococci is less straight forwardthan that of PMN. On the one hand, depletion of circu-lating monocytes enhances the severity of sepsis and there-by increases the risk of septic death. On the other hand,the severity of joint in£ammation and destruction are sig-ni¢cantly less pronounced [26]. These seemingly contradic-tory outcomes may be attributed to the activities of themajor mediators of monocyte/macrophage responses, thatis cytokines such as tumor necrosis factor (TNF). TNFand some other in£ammatory cytokines (see below) arenecessary to activate PMN to provide e⁄cient phagocyto-sis and killing of bacteria. However, a surplus of thesecytokines in the joint cavity triggers severe in£ammationwhich leads to cartilage and bone destruction [27]. Yetanother property of monocytes/macrophages is antigen-presentation, which is of major importance for acquiredimmune responsiveness. We have assessed whether micethat were isogeneic for the major histocompatibility com-plex (MHC) displayed di¡erent outcomes for staphylococ-cal arthritis. Our results indicated that this was indeed thecase, since mice that expressed certain MHC haplotypeswere better protected against the infection [28]. Such anoutcome may be due to di¡erential expansion capacity ofcertain T cell receptor families in response to staphylococ-cal superantigens depending on host MHC background[29].Additional cells, including platelets and natural killer

(NK) cells have also been studied in the setting of staph-ylococcal infections. As in the case of PMN, platelets areable to release bactericidal substances such as platelet mi-crobicidal proteins and PLA2 [1]. Their role in septic ar-thritis is currently unclear. The role of NK cells has beenstudied in some detail in the case of staphylococcal arthri-tis. E⁄cient depletion of the NK cell population using aspeci¢c monoclonal antibody leads to signi¢cantly in-creased frequency and severity of arthritis [30]. In sum-mary, with the important exception of monocytes/macro-phages, deletion of the cells of the innate immune systemleads to a clear worsening of staphylococcal infection.Adhesion molecules and selectins, important factors in

cell migration, promote extravasation of leukocytes direct-ing them to the site of infection. ICAM-1 deletion leads todecreased joint in£ammation in septic arthritis [31]. Also,integrin-associated protein-de¢cient mice are less suscepti-ble to developing S. aureus-induced arthritis [32]. Finally,P- and L-selectins were shown to be required for optimal

staphylococcal clearance. While P-selectin deletion de-creased joint pathology, expression of L-selectin did notchange the outcome of the joint manifestations [33]Many of the key soluble components of the innate re-

sponse to staphylococci originate from cells that are notintrinsically immune cells, e.g. hepatocytes, endothelialcells, and epithelial cells. Encountering staphylococci dra-matically increases systemic concentration of moleculesproduced by these cells and permits their local exudationat the sites of infection. Proteins that participate in thecomplement cascade are one example of soluble compo-nents of the immune system. In vivo administration ofcobra venom factor leads to a temporary inhibition ofthe complement system, and aggravates both S. aureussepticemia and arthritis [34]. This outcome is due to thedecreased opsonization of staphylococci, thereby leadingto less e⁄cient phagocytosis. The role of yet another im-portant participant of the innate immune response, nitricoxide, has been studied in detail by us and others [35,36].The results obtained, irrespective of whether synthetic NOinhibitors or genetic inactivation of NO-synthase were em-ployed, show clearly that this molecule provides protectionagainst S. aureus arthritis. Finally, the coagulation and¢brinolytic systems are often activated during severe in-fections. This is indeed the case when mice are systemicallyinfected by S. aureus. This condition is characterized by ahypercoagulable state with predominant activation of theexternal coagulation pathway which is registered as anearly increase of tissue factor activity and a concomitantreduction of protein C activity [37]. Follow-up studieshave shown that tissue factor itself is in£ammatogenicwhen administered to healthy mouse joints [38]. Morepronounced arthritogenicity was found when complexesof tissue factor and its natural ligand (i.e. factor VII)were administered intra-articularly [39].

6. Cytokines and chemokines involved in host reactivityagainst staphylococci

Cytokines are low molecular mass proteins functioningas signals between cells. These proteins are typically pro-duced under homeostatic conditions but are readily de-tected at high concentration in response to cellular stress.They act mostly locally but also in an endocrine way.Cytokines display a wide range of properties. In addition,their impact on disease outcome may vary depending onthe local concentration as well as time point for theirsecretion in relation to the start of the disease. Using asensitive in situ hybridization method we have assessedsynovial tissue frequency of cytokine- and chemokine-ex-pressing cells during S. aureus arthritis. Our results indi-cate early upregulation of predominantly macrophage-de-rived TNF and interleukin (IL)-1L mRNA. Expression ofT cell-derived cytokine mRNA was detected later and at arelatively low frequency. Notably, induction of Th2 cyto-

FEMSLE 10747 28-11-02

A. Tarkowski et al. / FEMS Microbiology Letters 217 (2002) 125^132128

kine (IL-4, IL-10) expression preceded the appearance ofTh1 cytokine (interferon-Q, TNFL) mRNAs [4]. Using ge-netically modi¢ed mice, we have next assessed the impactof cytokine gene deletion on the outcome of septic arthritisand sepsis. The macrophage-derived cytokines TNF, IL-1,and IL-12 mediate protection against septic death due totheir properties of an e⁄cient bacterial clearance. Interest-ingly though, despite overall protective e⁄cacy of TNFwith respect to decrease of bacterial load, local secretionof TNF in the joint cavity gives rise to increased severityof joint manifestations during septic arthritis. This empha-sizes a major role for TNF in attracting in£ammatory cellsto the joint cavity and inducing sequelae. The results ofthese studies are summarized in Table 1.

7. Is acquired immune responsiveness bene¢cial ordetrimental during staphylococcal infection?

T- and B-lymphocytes are the only cells that participatein acquired immune responses. In general, the participa-tion of T cells may be studied by assessing T cell in¢ltratesin the synovial tissue during septic arthritis. Our resultsindicate that T cells of predominantly CD4 phenotypehome to the joints within a few days of bacterial inocu-lation. The majority of these CD4þ cells express a rela-tively unusual VL11 TCR family that is only rarely foundoutside the joints [9]. Further studies have shown thatthese T cells respond to TSST-1, a superantigen that isproduced by the infecting S. aureus. Interestingly, deletionof either all of the CD4þcells or the small population ofVL11 TCR-expressing CD4þ cells clearly ameliorates botharthritis and sepsis-triggered mortality [9,40]. A similaroutcome was obtained using a rat model of S. aureusarthritis and an antibody that deleted all K/L TCR-ex-pressing lymphocytes [41].The role of B cells and their subpopulations has been

studied in some detail. Mice that were totally deleted for Bcells using a gene-targeted approach and thus being agam-maglobulinemic showed striking similarities to congeneic

littermates with respect to the development of S. aureusarthritis and mortality [42]. This ¢nding indicates that theentire B cell compartment is of minor importance in thedefence against severe S. aureus infection. Interestingly,when only the B1 subpopulation of B cells was absent,as is the case in X-linked immunode¢ciency due to Bru-ton’s tyrosine kinase mutation, the mice were partly pro-tected to developing S. aureus arthritis [43]. Further anal-ysis of the results indicated that increased interferon-Qproduction along with low IL-1L and IL-6 synthesis, pro-vided the favorable outcome of the infection [43].Altogether, analysis of the acquired immune responsive-

ness during severe staphylococcal infection suggests thatcells participating in bacterial recognition are harmfulrather than protective, in contrast to what is found inthe case of innate immune responses.

8. Induction of protective immunity to the staphylococci

Staphylococcal infections do not per se induce protec-tive immunity in the host. Indeed, recurrent infections areoften seen even in immunocompetent subjects that carryantibodies against staphylococcal components. This ¢nd-ing implies that either: (a) acquired immunity (mediatede.g. by speci¢c antibodies) is ine⁄cient against S. aureusinfection, or (b) bacterial epitopes that have the potentialto induce protective immunity during infection are notrecognized by the host. Bearing in mind the increasingnumber of known virulence determinants in staphylococci,we and others decided to investigate those factors thatmight provide protection upon hyperimmunization. In-deed, repetitive immunization with either highly puri¢edor recombinantly obtained components of the staphylo-coccal cell wall (e.g. collagen-, ¢brinogen-, and ¢bronec-tin-adhesins, and capsular polysaccharides) induces pro-tection against invasive S. aureus infection. With respectto S. aureus arthritis, it has been shown that vaccination-triggered antibodies that are speci¢c for collagen and ¢-brinogen adhesins provide e¡ective protection upon sub-

Table 1Impact of cytokines on staphylococcal arthritis

Cytokine/knock out Mouse strain (injection of cytokine) Arthritis Survival Bacterial clearance Phagocytosis/IC killing Ref.

IL-1R B6 + 3 3 3 [53]IL-4 B6 3 (+) + = [54]

(IL-4) n.e. n.e. n.e. 3

129Sv n.e. 3 n.e. = [55](IL-4) n.e. n.e. n.e. 3

IL-10 Balb/c + (3) 3 = [56]IL-12 B6 (3) 3 +a-b = [57]

(IL-12) n.e. n.e. n.e. =IFN-QR 129Sv + (+)a-b +a-b n.e. [58]TNF/LTK B6 3 3 3 3 [27]TNF B6 (3) n.e. 3 n.e. [27]

Abbreviations: +, increase; 3, decrease; = , minor in£uence; (), no signi¢cant change; a, early; b, late; IC, intracellular; R, receptor; n.e., not exam-ined; LT, lymphotoxin.

FEMSLE 10747 28-11-02

A. Tarkowski et al. / FEMS Microbiology Letters 217 (2002) 125^132 129

sequent challenge with live staphylococci [5,6]. At least inthe case of collagen-adhesin-expressing staphylococcalstrains it was clear that infection itself was not enoughto trigger the synthesis of adhesin-speci¢c antibodies [5].In other cases, it has been shown that the induction ofadequate antibody responses requires modi¢cation of theantigen recognition. This is the case for capsular polysac-charide-speci¢c responses, where one needs to covalentlycouple the carbohydrate structure to a carrier protein toincrease the amount (and possibly the a⁄nity) of the spe-ci¢c antibodies [9,59]. Also, immunization with staphylo-coccal enterotoxins that were devoid of superantigenicitysigni¢cantly decreased the risk of severe staphylococcalinfection [44].Yet another speci¢c way to trigger protection is to in-

duce tolerance, i.e. speci¢c non-responsiveness, to toxiccomponents of the Staphylococcus. We have recently dem-onstrated that intranasal exposure of enterotoxins inducedincreased host production of IL-10, a cytokine with anti-in£ammatory properties. More importantly, repetitive in-tranasal exposure to the superantigen led to protectionagainst enterotoxin-triggered septic death [45]. Since alsostaphylococcal enterotoxins are virulence determinants[12,13,46], this approach might also prove to be e¡ectivein combatting septic arthritis.

9. New treatment modalities of already ongoingstaphylococcal infection

Despite the eradication of staphylococci by, for exam-ple, the use of e⁄cient antibiotics, tissue destruction con-tinues. This can clearly be seen in both human [47] andexperimental [48] septic arthritis and is caused by an ex-aggerated activation of the host immune response. Thus,there is considerable room for improvement with respectto the treatment of ongoing staphylococcal infections. Wehave shown that combined anti-in£ammatory and antibi-otic treatment clearly downregulates the severity of septicarthritis [48]. Furthermore, combined treatment with anantibiotic and the antioxidant, spin trap molecule phe-nyl-N-tert-butyl nitrone moderated the development of ar-thritis in S. aureus-infected mice [49]. Other approachesthat are presently being investigated in our laboratory in-clude the use of anti-in£ammatory cytokines and chlori-nated taurine, which is a modi¢ed amino acid that displaysboth anti-bacterial and anti-in£ammatory properties [50].The cellular systems that regulate host cytokine produc-tion, such as NF-UB and AP-1, represent alternative tar-gets for anti-in£ammatory therapies, not least in the caseof septic arthritis. We have shown that murine septicarthritis is, however, not e⁄ciently downmodulated byblocking the host NF-UB and AP-1 with antisense inhib-itors [51].Alternative treatment approaches include the use of en-

dogenous staphylococcal peptides that have the capacity

to downregulate septic arthritis [52]. A complete under-standing of the latter e¡ect is has not yet been attained.

10. Summary

During the past decade, the use of the experimentalmodel of staphylococcal arthritis has clari¢ed the involve-ment of numerous virulence factors, as well as many hem-atopoietic cell types and their products, in the pathogene-sis of infection. However, the mechanisms by whichstaphylococcal virulence factors act in vivo and themany details of the host^bacterium interaction remainlargely unknown. Recent advances in the in vivo imagingof bacteria and in the development of ex vivo detection ofbacterial/host gene activities should help us to resolvethese issues. More information is also required regardingthe risk factors for acquiring staphylococcal infection tofacilitate the appropriate selection of subjects for vaccina-tion. In addition, new methods must be developed to treatongoing infections with combinations of anti-in£amma-tory agents, anti-oxidants, passive immunization and anti-biotics in order to minimize the risk of sequelae. Exper-imental models of staphylococcal infections, such as themodel of septic arthritis described here are crucial for thedevelopment of novel therapeutic strategies.

Acknowledgements

The work has been supported by the Go«teborg MedicalSociety, Swedish Association against Rheumatism, KingGustaf Vs Foundation, Swedish Medical Research Coun-cil, Nanna Svartz’ Foundation, Bo«rje Dahlin’s Founda-tion, Swedish National In£ammation Network, SwedishNational Infection and Vaccination Network, LundbergFoundation, EU grant contact no. QLK2-CT-2002-01250,AME Wol¡ Foundation, and the University of Go«teborg.

References

[1] Collins, L.V. and Tarkowski, A. (2000) Animal models of experimen-tal Staphylococcus aureus infection. In: Gram-positive pathogens (Fi-schetti, V.A., Novick, R.P., Ferretti, J.J., Portony, D.A. and Rood,J.I. Eds.), pp 422^430. ASM Press, Washington, DC.

[2] Tarkowski, A., Collins, L.V., Gjertsson, I., Hultgren, O.H., Jonsson,I.M., Sakiniene, E. and Verdrengh, M. (2001) Model systems: mod-eling human staphylococcal arthritis and sepsis in the mouse. TrendsMicrobiol. 9, 321^326.

[3] Bremell, T., Abdelnour, A. and Tarkowski, A. (1992) Histopatholog-ical and serological progression of experimental Staphylococcus aure-us arthritis. Infect. Immun. 60, 2976^2985.

[4] Zhao, Y.X., Abdelnour, A., Ljungdahl, A., Olsson, T. and Tarkow-ski, A. (1995) Patterns of interferon-gamma mRNA expression intoxic shock syndrome toxin-1 expanded V beta 11+ T lymphocytes.Cell Immunol. 161, 28^33.

[5] Nilsson, I.M., Patti, J.M., Bremell, T., Hook, M. and Tarkowski, A.

FEMSLE 10747 28-11-02

A. Tarkowski et al. / FEMS Microbiology Letters 217 (2002) 125^132130

(1998) Vaccination with a recombinant fragment of collagen adhesinprovides protection against Staphylococcus aureus-mediated septicdeath. J. Clin. Invest. 101, 2640^2649.

[6] Josefsson, E., Hartford, O., O’Brien, L., Patti, J.M. and Foster, T.(2001) Protection against experimental Staphylococcus aureus arthritisby vaccination with clumping factor A, a novel virulence determi-nant. J. Infect. Dis. 184, 1572^1580.

[7] Palmqvist, N., Foster, T., Tarkowski, A. and Josefsson, E. (2002)Protein A is a virulent factor in Staphylococcus aureus arthritis andseptic death. Submitted.

[8] Abdelnour, A., Arvidson, S., Bremell, T., Ryden, C. and Tarkowski,A. (1993) The accessory gene regulator (agr) controls Staphylococcusaureus virulence in a murine arthritis model. Infect. Immun. 61,3879^3885.

[9] Jonsson, I-M., Mazmanian, S.K., Schneewind, O., Verdrengh, M.,Bremell, T. and Tarkowski, A. (2002) On the role of Staphylococcusaureus sortase and sortase-catalyzed surface protein anchoring in mu-rine septic arthritis. J. Infect. Dis. 185, 1417^1424.

[10] Nilsson, I.M., Lee, J.C., Bremell, T., Ryden, C. and Tarkowski, A.(1997) The role of staphylococcal polysaccharide microcapsule ex-pression in septicemia and septic arthritis. Infect. Immun. 65, 4216^4221.

[11] Liu, Z.Q., Deng, G.M., Foster, S. and Tarkowski, A. (2001) Staph-ylococcal peptidoglycans induce arthritis. Arthritis Res. 3, 375^380.

[12] Abdelnour, A., Bremell, T. and Tarkowski, A. (1994) Toxic shocksyndrome toxin 1 contributes to the arthritogenicity of Staphylococ-cus aureus. J. Infect. Dis. 170, 94^99.

[13] Abdelnour, A., Bremell, T., Holmdahl, R. and Tarkowski, A. (1994)Clonal expansion of T lymphocytes causes arthritis and mortality inmice infected with toxic shock syndrome toxin-1-producing staphylo-cocci. Eur. J. Immunol. 24, 1161^1166.

[14] Nilsson, I.M., Hartford, O., Foster, T. and Tarkowski, A. (1999)Alpha-toxin and gamma-toxin jointly promote Staphylococcus aureusvirulence in murine septic arthritis. Infect. Immun. 67, 1045^1049.

[15] Deng, G.M., Nilsson, I.M., Verdrengh, M., Collins, L.V. and Tar-kowski, A. (1999) Intra-articularly localized bacterial DNA contain-ing CpG motifs induces arthritis. Nat. Med. 5, 702^705.

[16] Deng, G.M., Verdrengh, M., Liu, Z.Q. and Tarkowski, A. (2000) Themajor role of macrophages and their product tumor necrosis factoralpha in the induction of arthritis triggered by bacterial DNA con-taining CpG motifs. Arthritis Rheum. 43, 2283^2289.

[17] Deng, G.M. and Tarkowski, A. (2000) The features of arthritis in-duced by CpG motifs in bacterial DNA. Arthritis Rheum. 43, 356^364.

[18] Deng, G.M., Liu, Z.Q. and Tarkowski, A. (2001) Intracisternallylocalized bacterial DNA containing CpG motifs induces meningitis.J. Immunol. 167, 4616^4626.

[19] Jonsson, I.M., von Ei¡, C., Proctor, R.A., Peters, G. and Tarkowski,A. (2002) Virulence of small colony variant Staphylococcus aureus inamurine model of septic arthritis. Submitted.

[20] Collins, L.V., Kristian, S.A., Weidenmaier, C., Faigle, M., van Kes-sel, K.P.M., van Strrijp, J.A.G., Gotz, F. and Peschel, A. (2002)Staphylococcus aureus strains lacking D-alanin modi¢cations of te-choic acids are highly susceptible to human neutrophil killing andare virulence-attentuated in mice. J. Infect. Dis. 186, 214^219.

[21] Peschel, A., Jack, R.W., Otto, M., Collins, L.V., Staubitz, P., Nichol-son, G., Kalbacher, H., Nieuwenhuizen, W.F., Jung, G., Tarkowski,A., van Kessel, K.P. and van Strijp, J.A. (2001) Staphylococcus aure-us resistance to human defensins and evasion of neutrophil killing viathe novel virulence factor MprF is based on modi¢cation of mem-brane lipids with l-lysine. J. Exp. Med. 193, 1067^1076.

[22] Jin, T., Bokarewa, M.I., McIntyre, L., Tarkowski, A., Corey, G.R.,Reller, L.B. and Fowler, V.G. (2002) Fatal infection outcome inbacteremic patients with staphylokinase de¢cient Staphylococcus au-reus strains. Submitted.

[23] Jin, T., Bokarewa, M., Foster, T., Mitchell, J., Higgins, J. and Tar-kowski, A. (2002) Staphylococcus aureus resists human defensins by

production of staphylokinase, a novel bacterial evasion mechanism.Submitted.

[24] Verdrengh, M. and Tarkowski, A. (1997) Role of neutrophils in ex-perimental septicemia and septic arthritis induced by Staphylococcusaureus. Infect. Immun. 65, 2517^2521.

[25] Peschel, A. and Collins, L.V. (2001) Staphylococcal resistance toantimicrobial peptides of mammalian and bacterial origin. Peptides22, 1651^1659.

[26] Verdrengh, M. and Tarkowski, A. (2000) Role of macrophages inStaphylococcus aureus-induced arthritis and sepsis. Arthritis Rheum.43, 2276^2282.

[27] Hultgren, O., Eugster, H.P., Sedgwick, J.D., Korner, H. and Tarkow-ski, A. (1998) TNF/lymphotoxin-alpha double-mutant mice resistseptic arthritis but display increased mortality in response to Staph-ylococcus aureus. J. Immunol. 161, 5937^5942.

[28] Abdelnour, A., Zhao, Y.X., Holmdahl, R. and Tarkowski, A. (1997)Major histocompatibility complex class II region confers susceptibil-ity to Staphylococcus aureus arthritis. Scand. J. Immunol. 45, 301^307.

[29] Zhao, Y.X., Brunsberg, U., Holmdahl, R. and Tarkowski, A. (1998)V beta 11+ T-lymphocyte expansion by toxic shock syndrome toxin-1di¡ers in mice bearing H-2q versus H-2b haplotypes. Immunology 94,1^4.

[30] Nilsson, N., Bremell, T., Tarkowski, A. and Carlsten, H. (1999) Pro-tective role of NK1.1+ cells in experimental Staphylococcus aureusarthritis. Clin. Exp. Immunol. 117, 63^69.

[31] Verdrengh, M., Springer, T.A., Gutierrez-Ramos, J.C. and Tarkow-ski, A. (1996) Role of intercellular adhesion molecule 1 in patho-genesis of staphylococcal arthritis and in host defense against staph-ylococcal bacteremia. Infect. Immun. 64, 2804^2807.

[32] Verdrengh, M., Lindberg, F.P., Ryden, C. and Tarkowski, A. (1999)Integrin-associated protein (IAP)-de¢cient mice are less susceptible todeveloping Staphylococcus aureus-induced arthritis. Microbes Infect.1, 745^751.

[33] Verdrengh, M., Erlandsson-Harris, H. and Tarkowski, A. (2000)Role of selectins in experimental Staphylococcus aureus-induced ar-thritis. Eur. J. Immunol. 30, 1606^1613.

[34] Sakiniene, E., Heyman, B. and Tarkowski, A. (1999) Interaction withcomplement receptor 1 (CD35) leads to amelioration of sepsis-trig-gered mortality but aggravation of arthritis during Staphylococcusaureus infection. Scand. J. Immunol. 50, 250^255.

[35] Sakiniene, E., Bremell, T. and Tarkowski, A. (1997) Inhibition ofnitric oxide synthase (NOS) aggravates Staphylococcus aureus septi-caemia and septic arthritis. Clin. Exp. Immunol. 110, 370^377.

[36] McInnes, I.B., Leung, B., Wei, X.Q., Gemmell, C.C. and Liew, F.Y.(1998) Septic arthritis following Staphylococcus aureus infection inmice lacking inducible nitric oxide synthase. J. Immunol. 160, 308^315.

[37] Bokarewa, M.I. and Tarkowski, A. (2001) Thrombin generation andmortality during Staphylococcus aureus sepsis. Microb. Pathog. 30,247^252.

[38] Bokarewa, M.I., Morrissey, J.H. and Tarkowski, A. (2002) Tissuefactor as a proin£ammatory agent. Arthritis Res. 4, 190^195.

[39] Bokarewa, M.I., Morrissey, J.H. and Tarkowski, A. (2002) Intra-articular tissue factor/factor VII complex induces chronic arthritis.In£amm. Res. 51, 471^477.

[40] Abdelnour, A., Bremell, T., Holmdahl, R. and Tarkowski, A. (1994)Role of T lymphocytes in experimental Staphylococcus aureus arthri-tis. Scand. J. Immunol. 39, 403^408.

[41] Bremell, T., Lange, S., Holmdahl, R., Ryden, C., Hansson, G.K. andTarkowski, A. (1994) Immunopathological features of rat Staphylo-coccus aureus arthritis. Infect. Immun. 62, 2334^2344.

[42] Gjertsson, I., Hultgren, O.H., Stenson, M., Holmdahl, R. and Tar-kowski, A. (2000) Are B lymphocytes of importance in severe Staph-ylococcus aureus infections? Infect. Immun. 68, 2431^2434.

[43] Zhao, Y.X., Abdelnour, A., Holmdahl, R. and Tarkowski, A. (1995)Mice with the xid B cell defect are less susceptible to developing

FEMSLE 10747 28-11-02

A. Tarkowski et al. / FEMS Microbiology Letters 217 (2002) 125^132 131

Staphylococcus aureus-induced arthritis. J. Immunol. 155, 2067^2076.

[44] Nilsson, I.M., Verdrengh, M., Ulrich, R.G., Bavari, S. and Tarkow-ski, A. (1999) Protection against Staphylococcus aureus sepsis by vac-cination with recombinant staphylococcal enterotoxin A devoid ofsuperantigenicity. J. Infect. Dis. 180, 1370^1373.

[45] Collins, L.V., Eriksson, K., Ulrich, R.G. and Tarkowski, A. (2002)Mucosal tolerance to a bacterial superantigen indicates a novel path-way to prevent toxic shock. Infect. Immun. 70, 2282^2287.

[46] Bremell, T. and Tarkowski, A. (1995) Preferential induction of septicarthritis and mortality by superantigen-producing staphylococci. In-fect. Immun. 63, 4185^4187.

[47] Lowy, F.D. (1998) Staphylococcus aureus infections. N. Engl. J.Med. 339, 520^532.

[48] Sakiniene, E., Bremell, T. and Tarkowski, A. (1996) Addition ofcorticosteroids to antibiotic treatment ameliorates the course of ex-perimental Staphylococcus aureus arthritis. Arthritis Rheum. 39,1596^1605.

[49] Sakiniene, E. and Collins, L.V. (2002) Combined antibiotic and freeradical trap treatment is e¡ective at combating Staphylococcus aure-us-induced septic arthritis. Arthritis Res. 4, 196^200.

[50] Verdrengh, M. and Tarkowski, A. (2002) Chlorinated taurine dis-plays anti-in£ammatory and bactericidal properties. Manus.

[51] Gjertsson, I., Hultgren, O.H., Collins, L.V., Pettersson, S. and Tar-kowski, A. (2001) Impact of transcription factors AP-1 and NF-kap-paB on the outcome of experimental Staphylococcus aureus arthritisand sepsis. Microbes Infect. 3, 527^534.

[52] Balaban, N., Collins, L.V., Cullor, J.S., Hume, E.B., Medina-Acosta,E., Vieira da Motta, O., O’Callaghan, R., Rossitto, P.V., Shirtli¡,

M.E., Sera¢m da Silveira, L., Tarkowski, A. and Torres, J.V. (2000)Prevention of diseases caused by Staphylococcus aureus using thepeptide RIP. Peptides 21, 1301^1311.

[53] Hultgren, O.H., Svensson, L. and Tarkowski, A. (2002) Critical roleof signaling through IL-1 receptor for development of arthritis andsepsis during Staphylococcus aureus infection. J. Immunol. 168, 5207^5212.

[54] Hultgren, O., Kopf, M. and Tarkowski, A. (1998) Staphylococcusaureus-induced septic arthritis and septic death is decreased in IL-4-de¢cient mice: role of IL-4 as promoter for bacterial growth. J. Im-munol. 160, 5082^5087.

[55] Hultgren, O., Kopf, M. and Tarkowski, A. (1999) Outcome of Staph-ylococcus aureus-triggered sepsis and arthritis in IL-4-de¢cient micedepends on the genetic background of the host. Eur. J. Immunol. 29,2400^2405.

[56] Gjertsson, I., Hultgren, O. and Tarkowski, A. (2002) Interleukin-10ameliorates the outcome of Staphylococcus aureus arthritis by pro-moting bacterial clearence. Clin. Exp. Immunol. (in press).

[57] Hultgren, O.H., Stenson, M. and Tarkowski, A. (2001) Role of IL-12in Staphylococcus aureus-triggered arthritis and sepsis. Arthritis Res.3, 41^47.

[58] Zhao, Y.X. and Tarkowski, A. (1995) Impact of interferon-gammareceptor de¢ciency on experimental Staphylococcus aureus septicemiaand arthritis. J. Immunol. 155, 5736^5742.

[59] Lee, J.C., Park, J.S., Shepherd, S.E., Carey, V. and Fattom, A. (1997)Protective e⁄cacy of antibodies to the Staphylococcus aureus type 5capsular polysaccharide in a modi¢ed model of endocarditis in rats.Infect. Immun. Oct. 65, 4146^4151.

FEMSLE 10747 28-11-02

A. Tarkowski et al. / FEMS Microbiology Letters 217 (2002) 125^132132