4th LECTURE Public Health BSc CONNECTING INNATE AND ADAPTIVE IMMUNITY: ANTIGEN PRESENTATION

Sinuses Trachea Lungs AIRWAY SYSTEM EYE Oral cavity Esophagus Stomach Alimentary tract GASTROINTESTINAL SYSTEM DAMAGE TO ANY OF THESE BARRIERS MAY LEAD TO INFECTION Kidney Bladder Vagina UROGENITAL SYSTEM WALDEYER RING Tonsils, adenoids Palatinal, pharyngeal lingual and tubar tonsils SKIN CONTACT SURFACES Physical, chemical, microbiological barriers

FIRST LINE OF DEFENSE

PHYSICAL, CHEMICAL AND MICROBIOLOGICAL BARRIERS Skin  Tight junctions  Keratin layer  Antibacterial peptides e.g. defensins  pH of 5.5  Fatty acids  Normal flora Burns  susceptibility to infections Eye  Tear film (oils, lactoferrin, mucin and lysozyme) Respiratory tract  Ciliary movement – constant outward flow  Mucus secretion  Coughing, sneezing CF - impaired cilia movement GI tract  Stomach: pH of 3-4; small intestine: pH of 6-8  Digestive enzymes  Mucus secretion  Antibacterial peptides e.g. defensins, cryptidins  Peristalsis, diarrhoea, vomiting  Normal flora H. pylori – making basic pH Urogenital tract  Flushing out  Vagina: pH of , normal flora (Lactobacillus  lactic acid)  Testis: spermin and zink in semen

The normal flora SKIN, NASO-ORO-PHARYNX, GUT, VAGINA Symbiotic, non-pathogenic microbes, living in „peaceful” commensalisms Beneficial features: Digesting non absorbable food compounds e.g. cellulose Producing vitamines, antimicrobial molecules, regulating pH Compete with pathogenic microbes – survival of the fittest Providing constant low-dose antigen exposure Helping the development of the immune system Maintainig tolerance MICROBIOLOGICAL BARRIERS Some facts about the normal flora: There are 100-times more bacterial genes than eukaryotic genes Cells of human body: 90% microbes, 10% human Gut bacteria: more than 500 microbial species (approx. 1.5 kgs) Human cell population: BALANCE! (antibiotics – probiotics)

Gut normal flora play an important role in: -Development of mucosal and systemic immunity -Normal development of peripheral lymphoid organs - Maintenance of basic level of immunity

MECHANISM OF DEFENSE IN GENERAL environmental changes (e.g. infection) recognition (by receptors) effector functions (e.g. to get rid of pathogens)

SENSINGRECOGNITION SIGNALING RESPONSE INNATE IMMUNITY CellsReceptors Signaling pathways Cell-Cell collaboration Effector functions DEFENSE SYSTEMS ADAPTIVE IMMUNITY SENSINGRECOGNITION SIGNALING RESPONSE

RECOGNITION RECEPTORS OF INNATE IMMUNITY Pattern Recognition Receptors (PRRs) –recognise molecular patterns as danger signals –can be classified as PRR families: Lectins Toll-Like Receptors (TLRs) Nod-Like Receptors (NLRs) RIG-Like Receptors (RLRs) Scavenger receptors molecular pattern: characteristic molecules that are expressed in high amounts by cells or microbes –Patogen-Associated Molecular Patterns (PAMPs): molecules that are expressed unlike human cells, usually essential for the survival or replication of pathogens –Damage-Assoiated Molecular Patterns (DAMPs): molecules released after cellular damage

EFFECTOR MECHANISMS OF INNATE IMMUNITY NATURAL KILLER CELLS PHAGOCYTIC CELLS COMPLEMENT SYSTEM

PHAGOCYTIC SYSTEM NEUTROPHIL - MACROPHAGE - DENDRITIC CELL  Defense against infectious diseases  Elimination of tumor cells  Transplantation rejection Gatekeeper function Sensing commensals and pathogens Rapid activation of innate immunity Priming adaptive immune responses Maintenance of self-tolerance

Mannose Eukaryotic cells Glucoseamin Mannose Galactose Sialic acid EXAMPLE FOR PAMP: MANNOSE Prokaryotic cells protein glycosylation is different in:

Macrophage/dendritic cells Mannose Receptor Mannose MANNOSE RECEPTORS IS A PRR EXPRESSED ON THE SURFACE OF PHAGOCYTES Bacterium

PHAGOCYTOSIS

INNATE IMMUNITY Pathogen recognition  PRRs (TLRs, lectins, NLRs, RLRs, scavenger receptors) Cell activation  Macrophage: phagocytosis, intracellular killing (reactive oxygen species (ROS), lysosomal enzymes), secretion of chemokines and cytokines (via gene activation) Antigen processing  Phagocytosis/endocytosis  degradation in phagolysosomes Antigen presentation (later)

ACUTE INFLAMMATION A rapid response to an injurious agent that serves to deliver leukocytes and plasma proteins to the site of injury

 Infections  Trauma  Physical and Chemical agents (thermal injury, irradiation, chemicals)  Tissue Necrosis  Foreign bodies (splinters, dirt, sutures)  Hypersensitivity or autoimmune reactions  Increased vascular diameter  increased flood flow  Increased vascular permeability  edema  Migration of leukocytes from the blood to the affected tissue (diapedesis/extravasation), accumulation, effector functions MAJOR COMPONENTS OF INFLAMMATION: TRIGGERS OF ACUTE INFLAMMATION:

ORDER OF INNATE CELLS APPEARANCE IN THE INFLAMED SITE

RESOLUTION OF ACUTE INFLAMMATION

THE TYPE I INTERFERON RESPONSE: ANTIVIRAL STATE plasmacytoid dendritic cells Plasmacytoid dendritic cells (pDCs) produce 1000x more type I interferon than other cells (Natural Interferon Producing Cells – NIPC) After viral infection they are accumulated at the T cell zone of the lymph nodes

NK CELLS Similar functions to cytotoxic T cells but: larger than lymphocytes no rearranged antigen- specific receptors contain large cytoplasmic granules respond fast, circulate in a partly activated state

RECOGNITION AND KILLING BY NK CELLS Contents of lytic granules: Perforin: forming pores in the target cell membrane  lysis Granzyme: inducing apoptosis in the target cell

activating surface enzyme Activating surface required! inactive precursors limited proteolysis COMPLEMENT SYSTEM

THE EFFECTOR FUNCTIONS OF THE COMPLEMENT SYSTEM 1.help inflammatory processes: –increase vascular permeability –recruit leukocytes 2.opsonize pathogens  facilitate recognition by innate immune cells 3.direct lysis of pathogens/cells (Membrane Attack Complex – MAC)

PRIMARY (CENTRAL) LYMPHOID ORGANS Places of the maturation (antigen-independent development) of lymphocytes: bone marrow: generation of lymphoid progenitors, maturation of B cells thymus: maturation of T cells (and NK cells)

SECONDARY LYMPHOID ORGANS/TISSUES LYMPH NODES SPLEEN TONSILS (Waldeyer’s ring) Diffuse lymphoid layers under the epithelial barriers: –SALT (skin-associated lymphoid tissue) –MALT (mucosa-associated lymphoid tissue) BALT (bronchus-associated lymphoid tissue) GALT (gut-associated lymphoid tissue) Sites of lymphocyte activation and terminal differentiation

SLO: THE MEETING OF INNATE AND ADAPTIVE CELLS

ACTIVATION OF T CELLS

T cells can only recognise antigens that are bound to MHC molecules!

THE OUTCOME OF INFECTION IN A POPULATION WITH POLYMORPHIC MHC GENESMHC-Gen v v v v v v v v v v v v v vvv v v v v v v v v v Example: If MHC X was the only type of MHC molecule Population threatened with extinction Pathogen that evades MHC X MHC XX Population is protected

Synthesized antigens – endogenous antigens (virus, tumor) Internalized antigens – exogenous antigens (any protein) Degrade protein antigens to peptides = processing Protein-derived peptides are presented by MHC (HLA) membrane proteins  antigen presentation MHC molecules present both self and non-self protein-derived peptides MHC class I molecules are expressed in all nucleated cells MHC class II molecules are expressed by professional antigen presenting cells ANTIGEN PRESENTING CELLS

Peptides of endogenous proteins (virus, tumor) bind to class I MHC molecules Tc Endogenous Ag RECOGNITION OF EXOGENOUS AND ENDOGENOUS ANTIGENES BY T-LYMPHOCYTES Exogenous Ag Th Peptides of exogenous proteins (toxin, bacteria, allergen) bind to class II MHC molecules

THE ENDOGENOUS ANTIGEN PROCESSING PATHWAY Tc Proteasome LMP2/LMP7 Intracellular PROTEINS TAP1/2 gp96 calnexin α-chain α-chain+β2mMHC+peptide MHC-I + Ag peptide MHC-I + self peptide CLOSEDFLEXIBLE cytoplasm MHC-I, LMP2/7, TAP IFN  induced coordinated expression

Th INVARIANT CHAIN (Ii) 1.Chaperone – conformation 2.Inhibition of peptide binding 3.Transport/retention CLOSEDFLEXIBLE Ii+αβ CLIP DMA/B DMA/DMB 1. Support the peptide receptive conformation 2. Exchange of CLIP for exogenous peptides MHC-II + Ag peptide MHC-II + self peptide THE EXOGENOUS ANTIGEN PROCESSING PATHWAY

The recognition of the MHC-presented peptide antigen is not enough for T cell activation!

DIFFERENTIATION OF CD4+ T CELLS The polarization of helper T cell response is regulated by multiple factors: –origin of the presented peptide –nature of the APC –microenvironment –etc. In case of an infection both Th1 and Th2 cells are generated in different sites of the secondary lymphoid organs Imbalance occurs in case of special disorers: –Th1 dominance: e.g. mycobacterial infection –Th2 dominance: e.g. allergy, SLE cellular, pro- inflammatory humoral, anti- inflammatory