Cutaneous Immunology HuBio 567—The Skin Fall 2002 University of Washington School of Medicine Roy Colven, MD Cutaneous Immunology Summary Points • The immune system protects us from foreign micro-invasion. • The immune system sometimes screws up. • The skin has its own immune system. • Inflammatory skin disorders are understandable. • New, more specific, treatments emerging. Cutaneous Immunology Overview I. Brief review of general immunology II. Skin immune system biology III. Skin immune system pathology Immunity Innate & Adaptive • First line of defense • Activated • Nonspecific • Very specific • Rapid onset • Slower • No protective • Protective immunity immunity possible • No memory • Memory possible • Phagocyte- • Lymphocyte- mediated mediated Adaptive Immunity Lymphocytes • Unique antigen receptor constructed early • Selected and activated by non-self proteins • Clones persist (memory cells) • Lymphocytes with self-recognizing receptors are culled B-cells T-cells •Mature in bone marrow •Mature in thymus •Lymphoid follicle •Paracortical area •Antigen receptor: •Antigen receptor: Immunoglobulin T-cell receptor molecule From, Janeway, CA, Immunobiology, 5th ed. Adaptive Immunity Antigen Receptors From, Janeway, CA, Immunobiology, 5th ed. Adaptive Immunity “Professional” Antigen Presenting Cells • Dendritic cells, macrophages, B-cells • Efficiently process antigens • Cytosolic and vesicular compartments • Express MHC I and II molecules • Antigen peptides fit in MHC cleft • MHC:peptide complex to cell surface • Provide costimulatory 2nd signal MHC Molecules • Function: Bind processed antigen and transport to cell surface • MHC I: – All nucleated cells – Process Ag from cytosolic compartment – Present to CD8+ cytotoxic T-cells – HLA-A, B, C • MHC II: – Dendritic cells, macrophages, B-cells – Process Ag from vesicular compartment – Present to CD4+ helper T-cells – HLA-DR, DP, DQ Antigen Presenting Cells From, Janeway, CA, Immunobiology, 5th ed. Adaptive Immunity Recipe for Successful Antigen Presentation Place in a lymph node... • 1 antigen presenting cell (APC) with MHC molcules (I or II) • 1 antigen processed by APC • 1 naïve T cell (CD8+ or CD4+) with unique and specific T-cell receptor • Add costimulatory second signal and a pinch of IL-2 • Stir.…Proliferate, differentiate! Adaptive Immunity To Activate a Lymphocyte… From, Janeway, CA, Immunobiology, 5th ed. Cytokines: More than Alphabet Soup • Cell communication via released peptides • High affinity receptors • Low concentration, big effect • Impact over short distances: Auto-, juxta-, paracrine • Wide range of cellular effects • Examples: Interleukins, TNF, interferons Cell Adhesion Molecules: Molecular Velcro • Cell surface molecules with matching ligands on other cells • Allow cell-to-cell binding for communication and homing • Expression of CAMs variable and under complex control • Example: Intercellular adhesion molecule-1 (ICAM-1) on APC’s binding to lymphocyte function-associated antigen-1 (LFA-1) on T-cells Effector T-Cells • CD8+ cytotoxic T lymphocyte (CTL) – “The Hitman” – Kills on contact • CD4+ helper T lymphocyte – “The Bureaucrat” – Directs other cells to do the dirty work Effector T-cells do not require costimulatory signal CD8+ Cytotoxic T-cell • Directly cytotoxic to cells via binding to Ag:MHC I complex • Cytosolic antigens (e.g., viruses) • Induces apoptosis • Cytotoxicity is specific and directional • Cytotoxins include: – Perforin, granzymes • Also produces cytokines – IFN-, TNF CD4+ Helper T-Cells • Binds to APCs via Ag:MHC II complex • Then directs other effector cells (macrophages, B cells) to kill pathogens or neutralize toxins • Uses cytokines as its “memos” Th1/Th2 Paradigm Cell-mediated immunity IL-2 Th1 TNF IL-12 IFN IL-10 Th0 Humoral immunity IL-12, IFN IL-4 IL-4 Th2 IL-5 IL-10 CD4+ Helper T-Cells: Th1/Th2 Paradigm • Th1 (type 1) – IL-2, TNF, IFN- – Activate macrophages and CTL’s for intracellular pathogen killing and cytotoxicity – Facilitate cell-mediated immunity – Inhibit Th2 cell proliferation CD4+ Helper T-Cells: Th1/Th2 Paradigm • Th2 (type 2) – IL-4, 5, 10 – Activate B cells and antibody production to neutralize extracellular pathogens & toxins – Facilitate humoral immunity – Inhibit Th1 cell proliferation What Determines Th1 vs. Th2 Response? • Type of pathogen • Innate immune response to it – Macrophages, NK cells release IL-12, IFN- – Mast cells, basophils, T cells release IL-4 • Host’s immune constitution • Density of Ag presented on APC – High density Th1 – Low density Th2 Cutaneous Immunology Overview I. Brief review of general immunology II. Skin immune system biology III. Skin immune system pathology Inherent (Nonimmune) Skin Defenses • Physical – Resistance to mechanical trauma – Relatively water impermeable – Physical separation between self and nonself • Chemical – Free fatty acids – Free radical trapping – Antimicrobial peptides Inherent Skin Defenses (cont’d) • Photoprotective – Melanin as a UV chromophore • Injury repair • Microbiological – Home for colonizing, nonpathogenic bacteria that: • Compete for nutrients • Compete for attachment • Produce antibacterial substances Innate Immune Features of the Skin • No specialization for skin • Cells – Phagocytes: Macrophages, neutrophils, NK cells – Mast cells • Circulating chemicals – Complement • Locally produced chemicals – Cytokines, histamine Mast Cells • Bone marrow-derived • Dermal resident • Perivascular • Mediators – Preformed (histamine, e.g.) – Newly synthesized (cytokines, e.g.) • Various stimuli mediator release – Immunologic: IgE binding antigen – Nonimmunologic: Physical, drugs, complement Mast Cells • ? Role in skin homeostasis – Nerve, blood vessel maintenance? • Function as initial responders – Pro-inflammatory effects • Vasoactive chemicals mediate urticaria – Histamine and leukotrienes Cells of the Cutaneous Adaptive Immune Response • Langerhans’ cell • Dermal dendrocytes • Keratinocytes • T-cells • Endothelial cells Cells of the Cutaneous Adaptive Immune Response • Macrophages • B-cells • Veiled cells ( T-cells) Langerhans’ Cells • Bone marrow-derived – Monocyte lineage • Transient epidermal cells • Dendritic cell – Cell surface molecules: CD1a, MHC II, ATPase, Fc receptor for IgG, C3 receptor, B7, several CAMs • Electron microscopy: Birbeck granules, convoluted nucleus Langerhans’ Cells: Epidermal Transients • Migration and maturation Bone marrow Blood (M) Epidermis (LC) Afferent lymph (VC) Lymph node (FDC) • Functions – Antigen capture and processing – Presentation of antigen – Costimulation of naïve T-cells – Produce activating cytokines Antigen Langerhans’ Cell Migration From Janeway, CA Immunobiology, 5th ed. Stoitzner, J Inv Dermatol, 2002 Stoitzner, J Inv Dermatol, 2002 Stoitzner, J Inv Dermatol, 2002 Stoitzner, J Inv Dermatol, 2002 Stoitzner, J Inv Dermatol, 2002 Dendritic Cell Maturation: LC FDC • Phagocytic • Ag processing • MHC I, II • Costimulatory molecules • Naïve T-cell stimulation • Birbeck granules + Dermal Dendritic Cells • Papillary dermis • Perivascular • Dendritic morphology • MHC II + • Subpopulations with phenotypic and functional overlap – Antigen presentation – Phagocytosis • Plasticity? Dermal Dendrocytes & Langerhans Cells: To Lump or Split Dermal dendrocytes Langerhans cells • No Birbeck granules • Birbeck granules • Factor XIIIa + • Factor XIIIa - • CD1a, ATPase - • CD1a, ATPase + • Blood vessel-assoc. • Epidermal Keratinocytes As Immune Cells Old view: Keratinocytes... • Are passive barrier cells • Are passive victims of immune attack Keratinocytes As Immune Cells Newer view: Keratinocytes... • Produce cytokines – e.g., IL-1, TNF-, Chemokines • Respond to cytokines – e.g., IFN, IL-1 • Upregulate ICAM-1 • Present antigen ...Particularly when stimulated Endothelial Cells & Cutaneous Inflammation • Increase permeability • When activated, endothelial cells... – cell surface expression of P-selectin for enhanced leukocyte margination – synthesis & expression of E-selectin for selective T-cell (CLA +) homing to the skin – expression of VCAM-1 & ICAM-1 to stop leukocytes and allow diapedesis » Immune response amplified Cutaneous Lymphocyte Antigen (CLA) • Specific skin homing marker on T-cells • CLA+ lymphocytes are memory/effector cells (CD45RO +) • Cell adhesion to endothelial cell – E-selectin is ligand • With cutaneous inflammation, E-selectin up-regulated, CLA+ cells selected T-Cells • Resident in epithelia; do not recirculate • Restricted T-cell receptors • Bridge between innate and adaptive immunity • Dendritic T-cell network found in mouse epidermis » Presence and function in human skin controversial The Skin Immune System Components 1. APCs: Langerhans cells, dermal dendrocytes, dermal macrophages 2. Keratinocytes 3. Endothelial cells 4. Skin-homing T-cells 5. Draining regional lymph vessels and nodes The Skin Immune System Principles 1. Interface with environment 2. Unique nonimmune protection 3. Innate immune defenses 4. Specialized set of APCs 5. Skin homing memory T-cells 6. Antigen presentation in skin 7. Distinct response from other epithelia Cutaneous Immunology Overview I. Brief review of general immunology II. Skin immune system biology III. Skin immune system pathology Contact Dermatitis • Erythematous, weepy, scaly, geometric plaques • Irritant- or allergen-induced • Major cause of occupational illness • Histology: Epidermal spongiosis Allergic Contact Dermatitis Pathogenesis Sensitization (Induction)--1o exposure • Contact allergen usually a hapten – LMW, links with endogenous protein • Picked up by LC’s and presented to naïve T-cells in lymph node • CLA upregulated on activated T-cells • Specific effector T-cells home to skin Often nothing happens…Why? Contact Allergen Contact Sensitization From Janeway, CA Immunobiology, 5th ed. Allergic Contact Dermatitis Pathogenesis • Elicitation--subsequent exposures • Allergen taken up by DC’s • Memory T-cells recognize Ag:MHC complex in situ (in the skin) • T-cells proliferate in situ – IL-2, TNF, IFN- expressed • Inflammatory response ensues Question: What turns this process off? Contact Elicitation From Janeway, CA Immunobiology, 5th ed. Allergic Contact Dermatitis Immunopathology Cell-mediated immunity IL-2 Th1 TNF IL-12 IFN IL-10 Th0 Humoral immunity IL-12, IFN IL-4 IL-4 Th2 IL-5 IL-10 Contact Dermatitis Irritant vs. Allergic • More common • Less common • Reaction minutes • No or delayed to hours after 1st reaction after 1st contact contact • Direct cellular • Ag presented to T- injury by chemical cells • No immunologic • Immunologic memory memory Atopic Dermatitis • Itch and xerosis • Acutely weepy to chronic dermatitis • Flexures, face commonly involved • Childhood onset often • Personal history of allergic rhinitis and/or asthma • Family history of atopy prominent • Histology: Epidermal spongiosis Atopic Dermatitis Immunopathology Cell-mediated immunity IL-2 Th1 TNF IL-12 IFN IL-10 Th0 Humoral immunity IL-12, IFN IL-4 IL-4 Th2 IL-5 IL-10 Staph antigens and Atopic Dermatitis Mechanisms of stimulation: • Innate immune response to infection • Superantigen stimulation of T cells • IgE sensitization to staph entero- toxins • Staph alpha toxin-mediated release of TNF from keratinocytes Leprosy (Hansen’s Disease) • Developing countries – India, African continent, Southeast Asia, South America, Mexico • Immigrants to US • Few cases acquired in US, related to armadillo exposure • Mycobacterium leprae • Clinical spectrum of disease correlates to immune response The Spectrum of Leprosy Lepromatous Tuberculoid Susceptibility Resistance Skin lesions/bacilli Cell-mediated immunity Antibodies Leprosy: Host Response Cell-mediated immunity IL-2 Th1 TNF IL-12 IFN Tuberculoid IL-10 Th0 Humoral immunity IL-12, IFN IL-4 IL-4 Th2 IL-5 IL-10 Lepromatous What Determines Immune Response in Leprosy? • Poverty, poor nutrition • Genetics – HLA-DR 2, 3 assoc. w/ tuberculoid form – HLA-DQ 1 assoc. w/ lepromatous form • Coexisting diseases, e.g., – HIV – Intestinal parasites? Pemphigus Vulgaris • Onset 5th-7th decades –Though can occur at any age • Oral erosions often presenting sign • Bullae are flaccid, erosions numerous and slow to heal; Nikolsky sign + • Histology: Suprabasal epidermal split • IF: Interkeratinocyte IgG Epidermal Targets of Autoantibody Attack Pemphigus vulgaris Bullous pemphigoid • Desmoglein 3 • BP Ag 1 (230 kD): (130 kD) Intra-basal keratinocyte • BP Ag 2 (180 kD): Transmembrane • Target: • Target: Desmosome Hemidesmosome – Keratinocyte cohesion – Dermal-epidermal junction adhesion Autoantibodies in Pemphigus are Pathogenic: Evidence • PV patients’ sera in skin culture evokes histologic changes of PV • Passive transfer of pemphigus IgG to neonatal mice causes disease • Transient PV in neonates of affected mothers The Cause of Autoimmunity as of September 13, 2001 Health Disease Something Happens Primary HIV Infection • Initial exposure to HIV leading to productive infection • 10-40% of cases asymptomatic • Associated with significant viremia • Transmission risk high • Ends with HIV seroconversion Dendritic Cells: Targets of HIV Infection • Langerhans cells (LCs) express CCR5 and CD4 • LCs prime target cell in epithelial transmission of HIV • HIV entry and productive infection can occur within LCs • LCs selective for M-tropic HIV strains Dendritic Cells as HIV Vectors • LCs can also trap and transport HIV without productive infection • LCs present HIV antigen to naïve T cells activation • HIV-specific activated T cells primed for HIV infection by LC vector HIV Immunopathogenesis: Strategic Attack • CD4+ T-cell ultimate target – Especially activated CD4 cells • HIV-specific CD4 response impaired early • Cytotoxic T lymphocyte response wanes over time • Progressive CD4+ lymphopenia • T-cell receptor repertoire crippled Significance of Recognizing Primary HIV Infection • Reduce transmission during period of high titer viremia Early intervention could... • lower viral set point • prevent establishment of sanctuary sites for HIV • allow the generation of an HIV-specific CD4 cell response Psoriasis • Affects 1-2% of population • Salmon-pink, sharply demarcated plaques with micaceous scale • Elbows, knees classic • Also common: scalp, trunk, genitals, nail involvement • Other variants: guttate, pustular, erythrodermic • Arthritis in 5% of psoriatic patients Psoriasis: Evidence of T-Cell Mediation • Early cells in psoriatic lesions • Cyclosporine, anti-CD4 monoclonal Ab’s as treatment • Blocking T cell:APC 2nd signal prevents psoriatic lesion • Psoriasis altered in HIV infection • Bone marrow transplant recipients • Streptococcal superantigens can induce psoriasis Psoriasis: New Immunologic Approaches to Treatment • TNF inhibition – Antibodies to TNF – Soluble TNF receptors • Costimulatory blockade • Adhesion molecule inhibition – LFA-1 – CD2 • IL-2 activation blockade Cutaneous Immunology Summary Points • The immune system protects us from foreign micro-invasion. • The skin has its own immune system. • The skin immune system isn’t perfect and sometimes screws up. • Inflammatory skin disorders are understandable. • New, more specific, treatments emerging.