JPEMS Nantes, Basic Immunology INNATE IMMUNITY

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1 JPEMS Nantes, Basic Immunology INNATE IMMUNITY Teacher: Pr. Régis Josien, Laboratoire d Immunologie and INSERM U1064, CHU Nantes Regis.Josien@univ-nantes.fr 1

2 Contents 1. General features and specificity of innate immune response 2. Recognition of microbes by the innate immune system 3. Components of innate immunity 4. Innate immune reactions 2

3 Contents 1. General features and specificity of innate immune response 2. Recognition of microbes by the innate immune system 3. Components of innate immunity 4. Innate immune reactions 3

4 The response to an initial infection occurs in three phases 4

5 Specificity and receptors of the innate and adaptive immunity 5

6 Innate immunity ü Constitute the first of defense againt microbes ü Highly conserved system during the evolution (preceding adaptive immunity) ü Mediated by cells (phagocytes, DCs, NK cells, innate lymphoid cells) and soluble molecules (complement, cytokines) ü Recognizes structures shared by various classes of microbes, not present on host cells and often essential for microbes survival (PAMPs) ü Recognizes also endogen molecules (DAMPs) ü Uses a limited number of receptors encoded in the germline ü Induces 2 types of reactions: inflammation (bacteria) and antiviral defense ü The innate immune response instructs the adaptive immune system 6

7 Contents 1. General features and specificity of innate immune response 2. Recognition of microbes by the innate immune system 3. Components of innate immunity 4. Innate immune reactions 7

8 Pathogens can be found in various compartments of the body and of the cell The innate immune system used molecular sensors to detect extacellular and intracellular microbes 8

9 Pathogens have different mebrane structures Ex: structure of bacterial walls 9

10 Pattern Recognition Receptors, PRRs Recognize various pathogen associated molecular patterns (PAMPs): shared by several classes of microbes not expressed by host cells (self non-self discrimination) often critical for microbe survival and infectivity Some PRR can also recognize molecules released by damaged or necrotic cells: damage-associated molecular patterns (DAMPs) Non clonal expression (identical receptors on different cells) Immediate response 3 classes of PRR : 1. Secreted Molecules. Ex: mannane-binding lectin 2. Endocytic PRR. Ex: macrophage mannose receptor 3. Signalisation PRR. Toll-like receptors (TLR); NOD-like receptors (NLR), RIG-like receptors (RLR), C-type lectin-like 10 receptors (CLR)

11 Secreted PRR: ex: mannane-binding lectin (MBL) General functions of secrecred PRR: Opsonisation Complement activation Others: C-reactive protein (CRP) surfactants 11

12 Endocytic PRRs MMR: macrophage mannose receptor MMR 2 families: - Lectins - Scavenger receptors 12

13 Signalisation PRR Ø PRR recognizing microbes and damaged cells Ø Binding of ligand to PRR triggers intracellular activation leading to the activation of specific transcription factors Ø These transcription factors induce production of cytokines and adhesion molecules in phagocytes and dendritic cells Ø Distinct PRR stimulations lead to specific transcription factor activation and responses (inflammation vs. antiviral response) Ø These PRR are critical for inducing costimulation molecules expression and therefore adaptive immune responses 13

14 Cellular locations of receptors of the innate immune system 14

15 Toll-like receptors or TLR Toll = Drosophila gene controlling dorso-ventral polarisation (Anderson et al., Cell 1985, ) Major role in immune responses in Drosophila. Induces production of Drosomycine, a fongicidal peptide (Lemaitre et al., Cell 1996, 86:873) Vertebrate counter part: Toll-like receptor (TLR4) Nature 1997, 388:394) 10 members in human: TLR1-TLR10 (Medzithov et al., 15

16 TLR structure Domaine Ig Leucinrich repeat (LRR) Domain TIR (Toll-IL-1 R) Akira et Takeda, Nat Rev Immunol 2004, 4:499 16

17 Structure and specificities of TLR TLR10: ligands unknown 17

18 Signaling functions of TLR 18

19 Adaptor molecules in TLR signaling MyD88: myeloid differentiation primary-response protein 88 TIRAP: TIRdomaincontaining adaptor protein (TLR 2 et 4) TRIF: TIRdomaincontaining inducing IFN-β (TLR 3 et 4) TRAM: TRIFrelated adaptor molecule (TLR 4)

20 Cooperation and synergy between TLR Trinchieri G. and Sher A. Nat Rev Immunol. 2007, 7:179

21 21

22 NOD-like receptors (NLR) and the inflammasome NOD= nucleotide olimerization domain 22

23 Signalisation PRR RIG-I: retinoic acid inducible gene I

24 Contents 1. General features and specificity of innate immune response 2. Recognition of microbes by the innate immune system 3. Components of innate immunity 4. Innate immune reactions 24

25 Mechanisms of protection of epithelial barriers 25

26 Phagocytes Monocytes/macrophages (mononucleated phagocytes) Neutrophils (polymorphonuclear cells) 26

27 Cells of the immune system Lymphoid progenitor HSC Myeloid progenitor GM precursor Hemogram: Leuk: /mm3 Neutr: 52-75% Lympho: 20-45% Mono: 3-9 % Eosino: 0-5% Baso: 0-1,5 % DC: 0,1-0,5% Gran. Prec. M-CSF Monocytes- DC precursor G-CSF FLT3L Blood and lymph nodes B T Lymphocytes NK ILCs Innate lymphoid cells Eosinophil Basophil Neutrophil Polymorphonuclear cells Monocyte PreDC Blood plasmocytes 27 Tissues antibodies Mastocyte Macrophage Dendritic cell

28 Maturation of mononucleated phagocytes 28

29 Monocytes/macrophages Monocytes: Circulating cells ( /ml) ½ life: 2-3 days Specific surface marker: CD14 Macrophages (MØ): Tissular ½ life: long (until several months) Differentiation varies with microenvironnement Recent data indicate that most tissue MØ derive actually from embryonic cells and self renew locally Activity: proinflammatory ou favoring tissue repair 29

30 Activation and functions of macrophages 30

31 Infection stimulates macrophages to release cytokines chemokines and lipid mediators that initiate an inflammatory response médiateurs lipidiques Inflammatory cytokines : TNF-α, IL-1, IL-6 Lipid mediators of inflammation: prostaglandins, leucotriens and platelet activating factor (PAF) Roles of inflammation: 1. Recrutement of cellular and soluble effectors 2. Limit pathogen dissemination 3. Initiate tissue repair 31

32 Classical and alternative macrophage activation 32

33 Neutrophils Circulating cells (> 50% of leucocytes), not found in healthy tissus but recruted in large numbers if inflammation Polynucleated + granules which stain for acidic and basic colorants (May Grünwald Giemsa) Role: phagocytosis +++ and bactericidal Production in bone marrow increase ++ in response to infection Infectious risk +++ if neutropenia (+++ if < 500/mm 3 ) ½ life: short (6-10 h in blood) Die rapidly after phagocytosis: elimination by MØ and pus 33 formation

34 Eosinophils and basophils Are not phagocytes Mostly secretory functions Eosinophils: Granulation stained with acidic colorants (eosin orange in MGG) Bone marrow production induced by IL-5 Circulating cells; also found in large number in gut mucosa (role?) Proinflammatory functions: secretion of basic proteins (cationics): MBP, ECP Role in responses to parasites ++ and allergies 34

35 Eosinophils et basophils Basophils: Granulations stained with basic colorants (violet in MGG) Found in pathological tissues (parasites, allergies) Differentiation and activation induced by IL-3 Role in allergic response (immediate) +++ Maybe a role in antigen presentation? Secretory functions: cytokines, chemokines 35

36 Mast cells Cells constitutively present in skin and mucosal epithelium (not in the blood) Can be activated by TLR and antibody (IgE)-dependent mechanisms Secretory functions: vasoactives amines (histamin), enzymes, cytokines chemokines, lipid mediators Promote strong inflammation Role in responses to helminths and allergies

37 Dendritic cells Phagocytic cells Main function: antigen presentation to naive T cells Lesson#4 37

38 NK cells Complement è Lesson#3 38

39 Contents 1. General features and specificity of innate immune response 2. Recognition of microbes by the innate immune system 3. Components of innate immunity 4. Innate immune reactions 39

40 Innate responses to bacteria: inflammation Ø Inflammatory cytokines Ø Recrutement of phagocytes to inflammatory tissues Ø Phagocytosis and killing of microbes 40

41 Acute inflammatory response 41

42 Activated macrophages secrete cytokines with local and systemic effects 42

43 Cytokines produced by macrophages induce production of acute phase proteins in liver Acute phase proteins have anti-bacterial functions: ( = CRP ) Opsonisation Complement activation 43

44 Neutrophil extravasation. Step 1= rolling 44

45 Leukocyte rolling 45

46 Steps of neutrophil extravasation 46

47 Leukocyte extravasation 47

48 Phagocytosis and intracellular killing of microbes 48

49 Mechanisms of respiratory burst H2O2 O2- SOD NOX 49

50 Bactericidal agents produced or released by phagocytes on the ingestion of microorganisms 50

51 Chemotaxis of neutrophils Bacteria produce the tripeptide formyl-met-leu- Phe (fmlp) that is chemoattractant for neutrophils 51

52 Innate responses to virus 52

53 PRR involved in virus recognition Viral PAMPs PRR Transcription factor

54 Cellular sources of type I IFN 1. Plasmacytoid dendritic cells: a subset of leukocytes specialized in the recognition of virus and the production of massive amounts or type I IFN 2. All virus infected cells 54

55 Anti-viral action of type I interferons 55

56 Interferons are antiviral proteins produced by cells in response to viral infection 56

57 57

58 Role of innate immunity in stimulating adaptive immune responses 58

59 Role of TLR in induction of adaptive immunity 59 Medzhitov, Nat Rev Immunol 2001, 1:135