2. HOW THE IMMUNE SYSTEM WORKS Václav Hořejší Inst. of Molecular Genetics AS CR, Prague, Czech Republic

3. BASIC TASKS: - PROTECTION FROM PATHOGENS - REMOVAL OF ABNORMAL SELF CELLS

4. RECOGNITION

5. RECOGNITION OF PATHOGENS AND ABNORMAL SELF CELLS BY MEANS OF: - SURFACE RECEPTORS - “SOLUBLE RECEPTORS”

6. INNATE (NON-ADAPTIVE) SYSTEM

7. 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

8. MANNOSE-BINDING LECTIN, COMPLEMENT

9. TOLL-LIKE RECEPTORS

10. SURFACE LECTINS

11. 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).

12. ADAPTIVE (ANTIGEN-SPECIFIC) SYSTEM

13. 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.

14. B CELL DIFFERENTIATION

15. T LYMPHOCYTE DEVELOPMENT AND SELECTION IN THYMUS

16. T-CELL RECEPTORS: MAINLY RECOGNITION OF MHC-PEPTIDE COMPLEXES ON OTHER CELL’S SURFACE PURPOSE: DETECTION OF CELLS INFECTED BY “HIDDEN” INTRACELLULAR PARASITES (e.g. VIRUSES)

19. PRODUCTIVE STIMULATION OF T LYMPHOCYTES REQUIRES PROFESSIONAL APC (DC) AND COSTIMULATION

20. T LYMPHOCYTES: IMPORTANT FUNCTIONAL SUBSETS

22. Leo A., Schraven B.Curr Opin Immunol 2001 Jun;13(3):307-16

24. BASIC DOGMA FOR THE ADAPTIVE RESPONSES: ANTIBODY RESPONSES (B, Th2) – EFFECTIVE FOR EXTRACELLULAR PARASITES INFLAMMATORY RESPONSES (Th1, Tc) – EFFECTIVE FOR INTRACELLULAR PARASITES MUTUAL INHIBITION Th1 vs. Th2 (POSITIVE FEEDBACK REGULATION) WRONG CHOICE Th1 vs. Th2 CAN BE FATAL (LEPROSY…)

25. Th1 x Th2

26. ESSENTIAL LINK BETWEEN THE INNATE AND ADAPTIVE SYSTEMS: DENDRITIC CELLS

28. DENDRITIC CELLS MUST BE PRE-STIMULATED BY DANGER SIGNALS TO BE ABLE TO ACTIVATE T LYMPHOCYTES

29. DANGER SIGNALS: - EXOGENOUS (PAMPs) - ENDOGENOUS (e.g. STRESS PROTEINS RELEASED FROM NECROTIC CELLS)

32. DISPOSAL

33. 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

34. PHAGOCYTOSIS

35. SELF-TOLERANCE

36. BIG PROBLEM: HOW TO MAINTAIN SELF- TOLERANCE AND PREVENT AUTOIMMUNITY?

38. IMMUNOLOGICAL HIT (WITH EMBARRASSING HISTORY…) REGULATORY (= SUPPRESSOR) T LYMPHOCYTES (Treg, Ts, Th3, Tr1…)

40. REGULATORY T LYMPHOCYTES ARISE IN: - THYMUS (SUPPRESS AUTOIMMUNITY) - PERIPHERY (THESE DOWN-REGULATE EXCESSIVE IMMUNE RESPONSES

41. PRACTICAL CONSEQUENCES?

42. HOPEFULLY: - BETTER VACCINES (WEAK ANTIGENS, TUMORS?) - IMMUNOSUPPRESSION (AUTOIMMUNE DISEASES, TRANSPLANTATION)

45. 21 st CENTURY – THE AGE OF IMMUNOTHERAPEUTICS? WE WILL SEE IN 20, 50, 100 YEARS…

46. 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)

47. MOLECULAR MECHANISMS: THOUSANDS OF MOLECULES, RECEPTORS, CYTOKINES, PATHWAYS…

48. Leo A., Schraven B.Curr Opin Immunol 2001 Jun;13(3):307-16

49. LIPID RAFTS (GEMs)

50. RAFTs - DISTRIBUTION AND HETEROGENEITY

51. GEMs IN IMMUNORECEPTOR SIGNALLING

52. TRANSMEMBRANE ADAPTOR PROTEINS (TRAPs) IN GENERAL Closely associated with immunoreceptors Not associated with rafts Associated with rafts (palmitoylated)

53. Signaling components of leukocyte rafts: Src kinases: Štefanová et al, Science 254(1991)1016 Cinek et al, J. Immunol. 149(1992)2269 Transmembrane adaptor LAT (critical for TCR signaling): Brdička et al, Biochem. Biophys. Res. Commun. 248(1998)356 Transmembrane adaptor PAG (activates Csk – regulation of Src-kinases): Brdička et al, J. Exp. Med. 191(2000)1591 Transmembrane adaptor NTAL (LAT-like function in BCR and FcR signaling): Brdička et al, J. Exp. Med. 196(2002)1617 Transmembrane adaptor p33 (a role in CD4, CD8 signaling?): Brdičková et al, submitted Collaboration with Burkhart Schraven (Heidelberg, Magdeburg)