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Structure and Function of the Skin:

Cancer, Immunity and Inflammation

The Cutaneous Microbiome

Heidi H. Kong, MD, MHSc, FAAD

Dermatology Branch

DISCLOSURE OF RELATIONSHIPS WITH INDUSTRY

Heidi H Kong, MD, MHSc, FAAD

C010: Structure and Function of the Skin: Cancer, Immunity and

Inflammation

The Cutaneous Microbiome

DISCLOSURES

No relevant conflicts to disclose

The Skin Microbiome

Complex host-microbial interactions

Host

Host defense

e.g. AMPs

Microbes

Commensal/Pathogen

Culturing/Sequencing

Skin

Microbes

Host

The Skin Microbiome

Skin

Microbes

Host

Physiology

Cornified keratinocytes

Temperature, pH, lipids

Immunology

Adaptive

Innate Toll-like receptors,

Antimicrobial peptides, etc.

Jalian, HR and Kim, J. 2008. Chapter 9 “Antimicrobial Peptides” In: Gaspari, AA, Tyring, SK, eds. Clinical and Basic

Immunodermatology. Guildford, United Kingdom: Springer (London).

Antimicrobial peptides

1200+ identified

Widespread distribution (plants & animals)

Ancient lineage

Broad spectrum

Grouped based on amino acid

composition (10-50 a.a.), size,

conformational structure

Antimicrobial peptides

Proposed Mechanism of action:

Cationic antimicrobial peptides associate with

negatively charged bacterial membrane

Leads to pores in the microbial membrane with

subsequent osmotic lysis and microbial cell deathJalian, HR and Kim, J. 2008. Chapter 9 “Antimicrobial Peptides” In: Gaspari, AA, Tyring, SK, eds. Clinical and Basic

Immunodermatology. Guildford, United Kingdom: Springer (London).

Ganz T. 2003. Nat Rev Immunol 3, 710-720.

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Jalian, HR and Kim, J. 2008. Chapter 9 “Antimicrobial Peptides” In: Gaspari, AA, Tyring, SK, eds. Clinical and Basic

Immunodermatology. Guildford, United Kingdom: Springer (London).

Many antimicrobial peptides have chemotactic properties

Jalian, HR and Kim, J. 2008. Chapter 9 “Antimicrobial Peptides” In: Gaspari, AA, Tyring, SK, eds. Clinical and Basic

Immunodermatology. Guildford, United Kingdom: Springer (London).

LL-37 (in blue) is found in keratinocytes, follicular epithelium, eccrine glands and neutrophils.

Granulysin (in yellow) is produced predominantly by T cells

LL-37 (cathelicidin) and granulysin expression in skin

LL-37:

- Chemotaxis

- Angiogenesis

- Wound healing

Granulysin:

- Chemotaxis

- Cytotoxic to tumor

cells

- Anti-inflammatory

- Graft rejection

Jalian, HR and Kim, J. 2008. Chapter 9 “Antimicrobial Peptides” In: Gaspari, AA, Tyring, SK, eds. Clinical and Basic

Immunodermatology. Guildford, United Kingdom: Springer (London).

• HNPs (in tan) are found in azurophilic granules of neutrophils

• HBDs (in magenta) are produced by keratinocytes and macrophages

HNPs (Human neutrophil peptides [α-defensins]) and HBD

(human β-defensin) expression in skin

HNPs:

- Increase TNFα & IL-1

in S. aureus activated

monocytes

HBD:

- Chemotaxis of T

cells & dendritic cells

- hBD-3 strengthens

epidermal tight

junction barrier

Jalian, HR and Kim, J. 2008. Chapter 9 “Antimicrobial Peptides” In: Gaspari, AA, Tyring, SK, eds. Clinical and Basic

Immunodermatology. Guildford, United Kingdom: Springer (London).

• RNAse 7 (in orange) is present in keratinocytes in the epidermis

• Dermcidin (in red) is found predominantly in sweat glands

• Psoriasin (in green) is found in keratinocytes, sebocytes and in follicular epithelium

RNAse 7, Dermcidin, and Psoriasin expression in skin

RNAse 7:

- Potent activity against

Enterococcus faecium

Dermcidin:

- Primary sweat AMP

Psoriasin:

- Most abundant AMP in skin

- Chemotaxis

- Induced by E. coli flagellin

Jalian, HR and Kim, J. 2008. Chapter 9 “Antimicrobial Peptides” In: Gaspari, AA, Tyring, SK, eds. Clinical and Basic

Immunodermatology. Guildford, United Kingdom: Springer (London).

Antimicrobial and immunomodulatory properties

Ong, PY, et al. 2002. N Engl J Med 347(15): 1151-1160.

AMPs are differentially expressed in psoriasis &

atopic dermatitis

HBD2 LL-37

Psoriasis PsoriasisNormal Normal

Chronic AD Chronic ADAcute AD Acute AD

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Reviewed in: Charles L Bevins & Fu-Tong Liu. 2007. Nat Med 13, 904 – 906.

Cathelicidin variant peptides induced by stratum corneum tryptic

enzyme (SCTE), which is increased in rosacea, promotes

enhanced pro-inflammatory responses

Skin diseases are associated with specific bacteria,

antimicrobial peptides and TLRs

Gallo, RL and Nakatsuji, T. 2011. J Invest Dermatol 131: 1974-1980.

Humans microbes are complex and multi-faceted

Microbes are more often considered pathogenic

Mycobacterium tuberculosis

Herpes simplex virus

Microbes perform functions important for human health

Vitamin synthesis

Development and activity of immune system

Inhibition of skin colonization by pathogens

Bacteria commonly found on skin

Duality of skin bacteria

Commensal vs pathogenic microbe

Staphylococcus epidermidis

Staphylococcus aureus

Corynebacterium spp.

Propionibacterium acnes

DNA sequencing is a powerful microscope for

microbial identification

Sequencing instrumentKong. Trends Molec Med. 2011

Collect superficial skin sample

Isolate DNA

Amplify DNA with primers

(bacteria = 16S rRNA gene)

DNA sequencing/analysis

Pipeline for skin microbiome studies

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Duality of skin microbes: commensal vs pathogen

Staphylococcus epidermidis

Major skin inhabitant

Frequent cause of nosocomial infections

Produce antibacterial products

Bacteriocins, Enzymes (Esp, a serine protease),

Phenol soluble modulins, etc.

Iwase et al. Nature 2010

Lai et al. J Invest Dermatol 2010

S. epidermidis produces antimicrobial products &

promotes host defense against pathogens via TLR2

Gallo RL, Nakatsuji T. J Invest Dermatol 2011.

S. epidermidis

phenol soluble modulins/

Skin injury releases host dsRNA activating TLR3 in keratinocytes.

S. epidermidis lipoteichoic acid (LTA) inhibits excess inflammation

via TLR2-dependent mechanism.

Gallo RL, Nakatsuji T. J Invest Dermatol 2011.

S. epidermidis can inhibit excess P. acnes-induced inflammation

P. acnes

miR-143

Wang Y et al. Appl Microbiol Biotechnol 2014.

Xia et al. J Invest Dermatol 2016.

TLR2

S. epidermidis

lipoteichoic acid

(LTA) inhibits excess

P. acnes-induced

inflammation via miR-

143/TLR2 interaction.

Naik S et al. Science 2012.

Skin commensals tune skin-resident T cells

Mouse model of leishmania

infection

In germ-free mice:

Reduced local skin inflammation and

effector T cell response

Adding S. epidermidis restores

immunity

SPF

GF

GF + S. epidermidis

In mice, neonatal skin exposure to commensal

can lead to immune tolerance

Scharschmidt T et al. Immunity 2015.

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Well-known pathogen

Self-limited to invasive infections

Atopic dermatitis

Job’s/AD Hyper IgE syndrome (STAT3 mutation)

Asymptomatic nasal colonization

20% permanently colonized

30-50% transiently colonized

S. aureus preferentially hemolyzes human blood to utilize iron from human hemoglobin as a nutrient

http://staphylococcusaureustreatment.com/images/staphylococcus_aureus_treatment_2.jpg

Duality of skin microbes: commensal vs pathogen

Staphylococcus aureus

Pishchany et al. Cell Host Microbe. 2010

Interactions with host & other bacteria

Hemolysins

Affinity for human hemoglobin

Phenol-soluble modulins

High levels produced by CA-MRSA

Streptococci very sensitive to PSMs (may partially explain CA-MRSA dominance)

Bacteriocins

http://staphylococcusaureustreatment.com/images/staphylococcus_aureus_treatment_2.jpg

Joo et al. J Biol Chem 2011

Duality of skin microbes: commensal vs pathogen

Staphylococcus aureus

Children with atopic dermatitisAge-matched controls

Kong, Oh…Segre. Genome Res 2012.

Staphylococcus spp increase during AD flares

Nakatsuji T et al. Sci Transl Med 2017

Commensal staphylococci can produce AMPs to

selectively kill S. aureus

Diphtheroids

Part of normal skin flora

C. accolens, C. pseudodiphtheriticum

Can release antipneumococcal free fatty acids from skin lipids

As a pathogen

Systemic infections

Immunocompromised patients, skin barrier defects

Erythrasma - C. minutissimum

Trichomycosis - C. tenuis

http://www.life.umd.edu/classroom/bsci424/Images/PathogenImages/CorynebacteriumGramStainChineseLetters.jpg

Bomar L et al. mBio 2016.

Zawar V. J Dermatol Case Rep. 2011

Duality of skin microbes: commensal vs pathogen

Corynebacterium spp.

Predominant skin inhabitant in oily sites

Breaks down sebum into fatty acids

Products active against bacteria, yeast & molds

Associated with

Folliculitis

Systemic infections

Acne

Many different strains of P. acnes in healthy vs acne pts

Possible therapeutic targets

http://microbewiki.kenyon.edu/images/thumb/6/61/P_acnes.jpg/250px-P_acnes.jpg

Duality of skin microbes: commensal vs pathogen

Propionibacterium acnes

Liu J et al. ISME J 2015.

Tomida S. et al. mBio. 2013.

Fitz-Gibbon S et al. J Invest Dermatol 2013.

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