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H OW THE IMMUNE SYSTEM WORKS Václav Hořejší Inst. o f Molecular Genetics AS CR, Prague, Czech Republic. BASIC TASKS : - PROTECTION FROM PATHOGENS - REMOVAL OF ABNORMAL SELF CELLS. RECOGNITION.
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HOW THE IMMUNE SYSTEM WORKSVáclav HořejšíInst. of Molecular Genetics AS CR, Prague, Czech Republic
BASIC TASKS:- PROTECTION FROM PATHOGENS- REMOVAL OF ABNORMAL SELF CELLS
RECOGNITION OF PATHOGENS AND ABNORMAL SELF CELLS BY MEANS OF:- SURFACE RECEPTORS - “SOLUBLE RECEPTORS”
SOLUBLE AND MEMBRANE RECEPTORS OF THE INNATE SYSTEM (MAINLY ON VARIOUS TYPES OF PHAGOCYTES) RECOGNIZE:PATHOGEN-ASSOCIATED MOLECULAR PATTERNS (PAMPs)The number of the innate receptors is limited, shared structural features are recognized
MANNOSE-BINDING LECTIN, COMPLEMENT
A SPECIAL SORT OF THE CELLS OF THE INNATE (NON-ADAPTIVE) SYSTEM ARE NK (NATURAL KILLER) CELLS.SPECIALIZE IN KILLING OF ABNORMAL SELF CELLS CONSPICUOUS BY LOW EXPRESSION OF MHC MOLECULES (e.g. many tumors).
THE ADAPTIVE SYSTEM:- Based on huge repertoir of B- and T-lymphocyte clones, each carrying a slightly different receptor (BCR or TCR)- The “soluble receptors” of the adaptive system are antibodies (= soluble BCR)- The system is “anticipating”, clonal, “wasteful”- Clonal receptors arise mainly by gene rearrangement and somatic mutations.
T LYMPHOCYTE DEVELOPMENT AND SELECTION IN THYMUS
T-CELL RECEPTORS:MAINLY RECOGNITION OF MHC-PEPTIDE COMPLEXES ON OTHER CELL’S SURFACEPURPOSE:DETECTION OF CELLS INFECTED BY “HIDDEN” INTRACELLULAR PARASITES (e.g. VIRUSES)
PRODUCTIVE STIMULATION OF T LYMPHOCYTES REQUIRES PROFESSIONAL APC (DC)ANDCOSTIMULATION
T LYMPHOCYTES: IMPORTANT FUNCTIONAL SUBSETS
BASIC DOGMA FOR THE ADAPTIVE RESPONSES:ANTIBODY RESPONSES (B, Th2) – EFFECTIVE FOR EXTRACELLULAR PARASITESINFLAMMATORY RESPONSES (Th1, Tc) – EFFECTIVE FOR INTRACELLULAR PARASITESMUTUAL INHIBITION Th1 vs. Th2 (POSITIVE FEEDBACK REGULATION)WRONG CHOICE Th1 vs. Th2 CAN BE FATAL (LEPROSY…)
ESSENTIAL LINK BETWEEN THE INNATE AND ADAPTIVE SYSTEMS:DENDRITIC CELLS
DENDRITIC CELLS MUST BE PRE-STIMULATED BYDANGER SIGNALS TO BE ABLE TO ACTIVATE T LYMPHOCYTES
DANGER SIGNALS:- EXOGENOUS (PAMPs)-ENDOGENOUS (e.g. STRESS PROTEINS RELEASED FROM NECROTIC CELLS)
EFFECTOR MECHANISMS OF PATHOGEN REMOVAL (FOLLOWING RECOGNITION BY EITHER INNATE OR ADAPTIVE RECEPTORS):- KILLING BY MIROBICIDAL PEPTIDES, REACTIVE OXYGEN SPECIES, OR OTHER“CHEMICAL WEAPONS”- PHAGOCYTOSIS- INFLAMMATION (BASED ON CYTOKINES, CHEMOKINES)- KILLING (NOT CURING!!)OF INFECTED CELLS
BIG PROBLEM:HOW TO MAINTAIN SELF-TOLERANCE AND PREVENT AUTOIMMUNITY?
IMMUNOLOGICAL HIT(WITH EMBARRASSING HISTORY…)REGULATORY (= SUPPRESSOR) T LYMPHOCYTES (Treg, Ts, Th3, Tr1…)
REGULATORY T LYMPHOCYTES ARISE IN:- THYMUS (SUPPRESS AUTOIMMUNITY)- PERIPHERY (THESE DOWN-REGULATE EXCESSIVE IMMUNE RESPONSES
HOPEFULLY:- BETTER VACCINES (WEAK ANTIGENS, TUMORS?)- IMMUNOSUPPRESSION (AUTOIMMUNE DISEASES, TRANSPLANTATION)
21st CENTURY – THE AGE OF IMMUNOTHERAPEUTICS?WE WILL SEE IN 20, 50,100 YEARS…
SUMMARY:- RECOGNITION BY SOLUBLE OR MEMBRANE-ASSOCIATED RECEPTORS- INNATE SYSTEM (LIMITED NUMBER OF PAMP-RECEPTORS)- ADAPTIVE SYSTEM (HUGE REPERTOIR OF HIGHLY SPECIFIC CLONAL RECEPTORS)- CRUCIAL ROLE OF DENDRITIC CELLS IN LINKING OF THE INNATE AND ADAPTIVE SYSTEM- DANGER SIGNALS (EXOGENOUS OR ENDOGENOUS) “WAKE UP” DC’s FOR STIMULATION OF T CELLS- CRUCIAL ROLE OF THE DECISSION FOR THE ANTIBODY-BASED (Th2) vs. INFLAMMATORY (Th1, Tc) RESPONSES- CRUCIAL ROLE OF SELF-TOLERANCE MECHANISMS (DELETION OF AUTOREACTIVE LYMPHOCYTES, REGULATORY T CELLS)
MOLECULAR MECHANISMS:THOUSANDS OF MOLECULES, RECEPTORS, CYTOKINES, PATHWAYS…
TMprotein TM protein CD48 TMprotein CD55 CD59 GLP LAT Lck Fyn LIPID RAFTS (GEMs)