4th LECTUREPublic Health BSc

CONNECTING INNATE AND ADAPTIVE IMMUNITY:

ANTIGEN PRESENTATION

SinusesTracheaLungs

AIRWAY SYSTEM

EYE

Oral cavityEsophagusStomach

Alimentary tract

GASTROINTESTINAL SYSTEM

DAMAGE TO ANY OF THESE BARRIERS MAY LEAD TO INFECTION

KidneyBladderVagina

UROGENITAL SYSTEM

WALDEYER RINGTonsils, adenoidsPalatinal, pharyngeal lingual and tubar tonsils

SKIN

CONTACT SURFACESPhysical, 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 3.8-4.5, 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: 1014 - more than 500 microbial species (approx. 1.5 kgs)• Human cell population: 1013

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)

SENSING

RECOGNITION

SIGNALING

RESPONSE

INNATE IMMUNITY

Cells

Receptors

Signaling pathways

Cell-Cell collaboration

Effector functions

DEFENSE SYSTEMS

ADAPTIVE IMMUNITY

SENSING

RECOGNITION

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 SYSTEMNEUTROPHIL - MACROPHAGE - DENDRITIC CELL

Defense against infectious diseases

Elimination of tumor cellsTransplantation rejection

Gatekeeper functionSensing commensals and pathogensRapid activation of innate immunityPriming adaptive immune responsesMaintenance 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 IMMUNITYPathogen 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 surfaceenzyme

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 GENES

MHC-Gen

vv

vv

vv

v

vv

v

v

v

v

v v v

v

vv

v

vv

v

vv

Example: If MHC X was the only type of MHC molecule

Population threatenedwith extinction

Pathogen that evades MHC

X

MHCXX

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

Golgi

ER

citoplazma

THE ENDOGENOUS ANTIGEN PROCESSING PATHWAY

Tc

ProteasomeLMP2/LMP7

Intracellular PROTEINS

TAP1/2gp96 calnexin

α-chain

α-chain+β2m MHC+peptide

MHC-I + Ag peptide

MHC-I +self peptide

CLOSEDFLEXIBLEcytoplasm

MHC-I, LMP2/7, TAP

IFN induced coordinated expression

Golgi

ER

CLIP

MCII

CIIV

DMA/B

li

M H C IIli

Th

INVARIANT CHAIN (Ii)

1. Chaperone – conformation

2. Inhibition of peptide binding

3. Transport/retention

CLOSEDFLEXIBLEIi+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