Immunodeficiency

• Definition:

• When the immune system is depressed or absent and an individual is unable to mount a normal immune response to satisfactorily protect the body.

Types of ImmunodeficiencyPrimary immunodeficiency: Inherited or congenital. Part of the

immune system is missing or does not function properly. Caused by defects in immune cell development or mutation in particular molecules. Severe form:present in early life.Less severe forms:may not cause problems until later in life.

Secondary immunodeficiency: previously functional immune

system compromised by factors outside the immune system, such as viruses, aging, radiation, malnutrition, severe stress, splenectomy, thymectomy or chemotherapy. More common than primary immunodeficiency.

From Immunobiology, Janeway et al.

ADA: Adenosine Deaminase

PNP: Purine nucleoside phosphorylase

From Immunobiology, Janeway et al.

Common ImmunodeficienciesDiGeorge’s Syndrome: thymic hypoplasia or

aplasia resulted from dysmorphogenesis of the third and fourth pharyngeal pouches during early embryogenesis.

Nude Mice or Rats.

SICD: Mice: Lack Rag

Bubble Boy: Lack c

The main features of antibody deficiencyDefective antibody production becomes critical 4-6 months after a full-term delivery when the maternally-derived IgG waned. The main manifestations are recurrent respiratory tract infections

Defective CD40 ligand expression by T cells: no class-switching from IgM and no germinal centers. BtK deficiency: X-linked agammaglobulinaemia due to failure of B cell lymphopoiesis. Clinically antibody deficiency is secondary to lymphoid malignancies: myeloma and chronic lymphocytic leukaemia.The main features of T cell deficiency

Defective T cell deficiency Increase in opportunistic infections: Pneumocystis carinii and Cryptosporidium. Mucosal yeast infectionDefects in T-dependent antibody responses

Di George syndrome HIV infectionDefects in RAG genes, IL-2 receptors, and expression of MHC antigens.

The main features of defects in neutrophilsSevere invasive bacterial (mostly gram negative) infections that respond poorly to antibiotics and are often lethal and invasive fungal infection.

Impairment of haemopoiesisAcute myeloblastic leukaemia: there is no stroma for neutrophil generation Cytotoxic drugs in cancer therapy -2 integrin deficiency: inability of neutrophils to migrate.

The main features of defects in complementDeficiency of C3: recurrent bacterial infections and infants are usually lethal. Deficiency of C5-9: normal health. Only increased risk of infection by particular bacteria

Acquired Immune Deficiency Syndrome (AIDS)• Caused by human immunodeficiency virus (HIV).• Infect mainly CD4+ T cells. Macrophages can also be infected and are very important as they

form a reservoir for a long term virus release.• When the immune system is weakened and cannot protect from serious infection, the

infected individual clinically had AIDS.• AIDS may appear as early as 2 years or as late as 10 years after infection with HIV. • 40 million people are infected with HIV. Around 5 million new cases in 2004 (15,000

new HIV infections a day!). More than 3 million died of AIDS in 2004.

Regional statistics for HIV & AIDS end of 2004

Region

Adults & Children

Living with HIV/AIDS*

Adults & Children Newly

Infected

Adult Infection Rate (%)

Deaths of Adults & Children*

Sub-Saharan Africa 25.4 3.1 7.4 2.3

East Asia 1.1 0.29 0.1 0.051

South and South-East Asia 7.1 0.89 0.6 0.49

Oceania 0.035 0.005 0.2 0.0007

Eastern Europe & Central Asia 1.4 0.21 0.8 0.060

Western & Central Europe 0.61 0.021 0.3 0.0065

North Africa & Middle East 0.54 0.092 0.3 0.028

North America 1.0 0.044 0.6 0.016

Caribbean 0.44 0.053 2.3 0.036

Latin America 1.7 0.24 0.6 0.095

Global Total 39.4 4.9 1.1 3.1 From Avert.org

http://www.accessexcellence.org/RC/VL/GG/images/Fig_9.30b.jpg

Protease inhibitorsThe pol region of the virion genome encodes a HIV protease that is an

aspartyl protease. Important for processing of essential functional protein products during the maturation of the virion. If the gag/pol polyprotein polyproteins are not cleaved, the virus fails to mature and is incapable of infecting a new cell.

HIV Vaccine

• No vaccine has been shown to be effective in humans.• Lack of good animal models.• Virus diversity.• Lack of proper adjuvants• Both humoral and cellular immunity are required.• Mobile Gp120 hinds epitopes.• Use of viral vectors and adaptation of co-stimulation

molecules and cytokines• Use of multiple epitopes• High Mucosal immune responses• Efficacy validation

Inflammation and Hypersensitivity

Inflammation: Definition• Purpose: Inflammation is a process by which the body attempts

to dilute, destroy or isolate a noxious agent and repair damage. The most potent effect of immune defense.

• Cause: The agents can be physical, chemical or biological.

• Process: Inflammatory response is characterized by the generation of inflammatory mediators and accumulation of fluid and leukocytes from the blood into extravascular tissues.

• The suffix "itis" means inflammation.

• It is a protective strategy, but goes too far too often.

• Management of inflammation is at least a part of almost all clinical practices.

Phases of Inflammation

•InitiationStructural changes leading to increase in blood flow and extravasation of fluid. Emigration of cells of the acquired and innate immune systems to the site of injury through chemotaxis.

•AmplificationElevated cellular metabolism and release of inflammatory mediators which promote local and systemic responses. Chemotactic factors to attract immune cells that invade surrounding tissues to fight infection (also cause damage).

•Termination Accomplished by specific inhibition or dissipation of the mediators. Growth factor will promote cell proliferation and repair.

Acute vs. Chronic Inflammation

• Acute inflammationImmediate and early response to tissue injury

Increase in capillary permeability and blood flow (Vasodilation)

Accumulation of fluid and plasma components

Intravascular stimulation of platelets

Presence of polymorphonuclear leukocytes (PMNs) (2-6 hr)

---Either resolved or goes on to chronic inflammation------Either resolved or goes on to chronic inflammation---

Injury or infection persist: Silicone implants, TB, ulcer, Injury or infection persist: Silicone implants, TB, ulcer, schistosomyosisschistosomyosis

Autoimmunity: RAAutoimmunity: RA

• Chronic inflammationAccumulation of macrophages (24 to 48 hr), and lymphocytes

(mononuclear cells) (5 to 7 days). Proliferation of fibroblasts (Fibrosis) and angiogenesis (weeks to months)

Acute vs. Chronic Inflammation

ACUTE CHRONIC

Vascular Changes Vasodilation Increased permeability

Minimal

Cellular Infiltrates Primarily neutrophils Mononuclear leukocytes, macrophages

Stromal Changes Minimal Edema and separation of layers

Fibrosis, cellular proliferation, scarring.

Margination and pavementing

Inflammatory Mediators

Bacterial Surface Polysaccharides

C3,C5

C3b,C5b

Membrane Attack Complex

Lysis of Bacteria

Opsonization

Phagocytosis

C3a,C5a

Chemotaxis

Ag/Ab (IgG,IgM)

Ag/Ab(IgE)

Mast CellActivation

Histamine release

Vasodilation

Collagen Basement Membrane

Coagulation

Plasmin

Bradykinin

Pain

Monocytes/MacrophagesPMNsEdema

Activity

1 2 3

REPAIR

(fibroblasts)

DAYS

Kinetics of Inflammation

Redness (ruber): Dilation of capillaries

Swelling (tumor): fluid containing plasma proteins and blood cells

Heat (calor): increase in blood flow

Pain (dolor): pressure on nerve; chemical mediators (e.g., bradykinin)

Loss of function (functio laesa): the fifth cardinal sign was, supposedly, added by German pathologist Rudolf Virchow (1821-1902).

Cardinal Signs of Inflammation

First described by Celsus (not Celsius) (10 BC-?)

Heat Redness Swelling Pain Loss of Function

Nature Reviews/Immunology

Chronic Inflammation

• Infiltration of lymphocytes, monocytes (transform to macrophages), plasma cells.

• Proliferation of fibroblasts and initiation of angiogenesis.

• Tissue destruction by inflammatory cells.

• Major causes of illness and dysfunction.

Mediators of Inflammation

• Vasoactive amines (histamine and serotonin (5-hydroxytryptamine,

5HT)). • Complement system (>30 proteins, 3g/L, 15% of globulin).

• Kinin system (bradykinin and kallidin)• Coagulation pathway • Fibrinolytic pathway (plasmin)• Arachidonic acid metabolites (prostaglandins, prostacyclin (PGI2),

leukotrienes, and thromboxanes)• Platelet activating factor• Cytokines• Free radical species

•Cell-derived (mostly preformed)

Proteins sequestered in granules

Membrane phospholipids (via arachidonic acid metabolism)

Vasoactive amines (mast cells and platelets)

•Inactive precursors in plasma, e.g.:

Complement proteins (C3a, C5a)

Coagulation proteins initiated by Hageman factor (FDPs)

Sources of Inflammatory Mediators

•Arachidonic acid metabolites

From cell membrane phospholipids through the action of phospho-lipases

Form leukotrienes via 5-lipoxygenase

Form prostaglandins and thromboxane A2 via cyclo-oxygenase (COX-1 inhibited by aspirin and indomethacin, COX-2 inhibited by Celebrex, VIOXX)

•Vasoactive amines (mast cells, eosinophils and platelets)

Histamine and 5HT– abundant in granules of mast cells and eosinophils

Serotonin – actions similar to histamine. Found in platelets. Released after platelet aggregation, or under the influence of platelet activating factor (PAF).

Chemical Mediators

By Richard E. Klabunde

Chemoattractants

• Exogenous mediators, e.g.:

N-formyl methionine terminal amino acids from bacteria (fMLP, formyl methionyl leucyl phenylalanine)

Lipids from destroyed or damaged membranes (including LPS)

• Endogenous mediators, e.g.:

Complement proteins (C5a)

Chemokines, particularly IL-8

Arachidonic acid products (LTB4)

Boyden Chamber

Shi et al. J Immunol Methods. 164:149

Chemokines

• Chemokines in their monomeric form have a molecular mass of 7-14 kDa

• Have in common highly conserved cysteine amino acid residues

1. CXC family - the first two NH2-terminal cysteines

separated by a single nonconserved amino acid; CXCL1-CXCL16

2. CC family - the first two NH2-terminal cysteines in juxtaposition

CCL1-CCL-27

3. C lymphotactin - one NH2-terminal cysteine amino acid XCL-1,2

4. CX3C fractalkine - the first two NH2-terminal cysteines separated by three nonconserved amino acid residues. CX3CL-1

Pattern Recognition Receptors (PRR)Pattern Recognition Receptors (PRR)

• Toll-Like Receptor Family (TLR1-10)Toll-Like Receptor Family (TLR1-10)– Expressed externally or internallyExpressed externally or internally– TLR4: LPS; TLR9: CpG; TLR4: LPS; TLR9: CpG; – Binding activates “pro-inflammatory” signaling pathways through Binding activates “pro-inflammatory” signaling pathways through

TRAF6TRAF6

• Phagocytic (endocytic) PRRPhagocytic (endocytic) PRR– Expressed on the surface of phagocytic cellsExpressed on the surface of phagocytic cells– Mediates uptake of microbes into phagocytesMediates uptake of microbes into phagocytes

• Secreted PRRSecreted PRR– Complement and Lectins, Secreted by Macrophage, epithelial cells, Complement and Lectins, Secreted by Macrophage, epithelial cells,

hepatocyteshepatocytes– Activate complement, opsonins, function as accessory proteins for Activate complement, opsonins, function as accessory proteins for

PAMP recognitionPAMP recognition

Receptor(Pattern Recognition

Receptors)

Agonist(s)(Pathogen-Associated Molecular Patterns)

TLR1 Heterodimerizes with TLR2

TLR2 PGN, some LPS, some LTA, lipoproteins, AraLAM

TLR3 dsRNA

TLR4 Gram(-) LPS, Taxol, some LTA, HSP60

TLR5 Flagellin

TLR6 Heterodimerizes with TLR2

TLR7 Imidazoquinoline

TLR9 Bacterial DNA (CpG)

TLR 8,10 Unknown

Toll-like Receptors and LigandsToll-like Receptors and Ligands

Systemic Effects of Inflammatory Cytokines

• Cytokines produced by monocytes/macrophages: TNF, IL-1, and IL-6.

•Shape the systemic response of the body to infection, and produce many signs and symptoms by which illness is recognized:

Fever

Elevated white cell count

Acute-Phase Response

Loss of appetite

Fatigue and sleepiness

Pain in muscles and joints

• Overproduction of inflammatory cytokines can produce the Systemic Inflammatory Response Syndrome [SIRS]:

Increased vascular permeability, leading to loss of blood volume

Vasodilation, with decreased blood pressure and tissue perfusion, organ dysfunction, shock, and death.

Septic shock

Summary of Inflammation

•Vascular Leakage: histamines, bradykinin, leukotreines (15-30’). TNF, IL-1 (endothelial contraction, 4 to 2h hours). Bacterial toxin (prolonged leakage); VEGF (transcytosis).

•PMN: Margination (selectins induced by TNF and IL-1), rolling (ICAM-1:LFA-1/Mac-1; VCAM-1:VLA-4); chemataxis(C5a, IL-8, LTB4); phagocytosis (attach, engulf, and degrade);Oxidative burst (Superoxide; hydrogen peroxide and nitric oxide)

•Clotting cascade: Collagen -> Factor VII ->fibrinogen ->fibrin.

•Kinin system: bradykinin and kallidin converted from plasma kininogens

•Complement: vasodilation and mast cell degranulation (C3a, C5a);chemotaxis (C5a); opsonization (C3b).

•Arachidonic Acid and Metabolites (Eicosanoids): prostagladins and thromboxane produced by cyclooxygenase

T Helper (CD4+ ) Subsets

Th2 responseHumoral Immunity

Acute Hypersensitivity

IL-4IL-10IL-13IL-5IL-6

Anti-InflammatoryCytokines

Th2TRAIL

IL-4

Th0

IFN-IL-2LT

Pro-InflammatoryCytokines

Th1

FasL

DR4

Th1 responseCellular Immunity

DTH

Suicide

Fas

Antigen

APC

IL-12

Hypersensitivities

Immune responses which are damaging rather than helpful to the host(In most cases). Trends Immunol. 2003 Jul;24(7):376-9.

Gell and Coombs proposed a classification scheme which defined 4 types of hypersensitivity reactions: (P.G.H. Gell and R.R.A. Coombs, The classification of allergic reactions underlying disease. In: R.R.A. Coombs and P.G.H. Gell, Editors, Clinical Aspects of Immunology, Blackwell Science (1963))

The first 3 are mediated by antibody (Th2), the fourth by T cells (Th1).

I IgE-mediated hypersensitivity(Anaphylactic)

II Antibody-mediated cytotoxic hypersensitivity(Cytotoxic)

III Immune-complex mediated hypersensitivity(Immune Complex)

IV Delayed-type hypersensitivity (DTH)

V(?) Granuloma (?)

Type I Hypersensitivity

-Rapid ('Immediate or anaphylactic') allergic reaction.

-Prior exposure to an antigen sensitizes a person to produce IgE. Re-exposure causes rapid degranulation of mast cells. The granule mediators causes acute inflammation: increase granulocytes, chemotaxis, and extravasation

-Primary mediators (stored):

Histamine and serotonin: vascular permeability, smooth muscle contractionECF-A-Eosinophil Chemotactic Factor of Anaphylaxis NCF-A-neutrophil Chemotactic Factor of Anaphylaxis Protease: Mucus secretion, connective tissue degradation

-Secondary Mediator (to be synthesized):

Leukotrienes: vascular permeability, sm contractionProstaglandins: vasodilation, sm contraction, platelet activationBradykinin: vascular permeability, sm contraction, PainCytokines: numerous effects

e.g.: Hayfever, asthma and allergic reaction to penicillin (phenoxymethylpenicillin and benzylpenicillin). Expulsion of worms and insect infections.

Tests: wheal-and-flare reaction (skin prick test for IgE) and RAST (radioallergosorbent test, blood allergen)

Type II Hypersensitivity

-By specific antibody (IgM or IgG) binding to cells or tissue antigens. FcR causes ADCC

Ab-dependent cellular immunity to bacteria and parasitesAutoimmunity

-By activating the classical complement pathway.

Blood transfusion (ABO incompatibility reaction) IgMRhesus disease (haemolytic disease of the newborn) IgG

Type III Hypersensitivity

Immune complexes: IgG with soluble antigens. Similar to type I except that IgG is involved. Preformed immune complexes bind to the low affinity FcRIII.

Pulmonary reactions to inhaled antigens:Occupational related diseases: Farmer’s lung.

The Arthus reactionA local type III hypersensitivity reaction in experimental models. Because the threshold for activation via FcRIII is higher than for FcRI, the reaction is slow (maximal at 4-8hrs) and more diffuse.

Generalized or systemic reactionsLarge amount of soluble Ag-Ab complexes in circulation and deposition in various organs such as skin joints, kidneys and blood vessels. The deposition causes inflammation, lesions and infection.

Rheumatoid Arthritis, Systemic lupus erythematosis, and serum sickness.

Type IV Hypersensitivity

-Delayed type hypersensitivity (DTH)-Mediated by antigen-specific type I helper T cells, not Ab.

APC (dendritic cells, or DC) present Ag in class II MHC groove, recognized by an antigen-specific TH1 cell. Cytokines (IFN, TNF) and chemokines are produced.

Macrophages, other T cells and, neutrophils accumulate to form granuloma. It is usually maximal at 48-72 hours.

The classical example is in tuberculosis: tuberculin test (Discovered by Robert Kock, 1905 Nobel Prize).

Allergy to metal salts and small reactive chemicals coupled to hapten.Rejection of transplanted organsSkin contact reaction to poison ivy.

http://www.info.gov.hk/dh/diseases/CD/photoweb

Type V Hypersensitivity (?)

-Granuloma -Evolutionarily conserved. In insects, ensheathment reaction

-In mammals, granulomas can be an immune reaction and are typified by the formation of epithelioid cells (modified macrophages).

-Type 1 cytokine mediated such as TB. -Type 2 cytokine mediated such as Schistosome infection.

http://ist-socrates.berkeley.edu/~jmp/TB1.htm

TYPE NAME INITIATION MECHANISM EXAMPLES

IIgE-mediated hypersensitivity(Anaphylactic)

2-30 minsAg cross-linking of IgE bound to mast cells; release of vasoactive mediators

Systemic anaphylaxis, Local anaphylaxis, Hay fever, Asthma, Eczema

II

Antibody-mediated cytotoxic hypersensitivity(Cytotoxic)

5-8hrsIgG to cell-surface antigens; cell destruction via ADCC or complement

ABO reactions; Rh in newborn; Autoimmune Haemolytic anemia

IIIImmune-complex mediated hypersensitivity(Immune Complex)

2-8hrs

Ag-Ab complex formed in serum and deposited in tissues; mast cell degranulation via FcRIII; chronic inflam.

Arthus reaction (Localized); autoimmune diseases

IVDelayed-type hypersensitivity (DTH)

24-72hrsTH1 cells release cytokines that recruit and activate macrophages

Contact dermatitis, Tubercular lesions

Summary of Hypersensitivity Reaction

V Granuloma (?)Months to Years

Formation of granuloma to encapsulate or isolate pathogens. Mediated by innate immunity or type 1 or type II cytokines

TB, Schistosomiasis

Immune Reaction