Immunità innata e reclutamento leucocitario

Transcription

1 Immunità innata e reclutamento leucocitario

2 Immunità innata: la prima linea di difesa Infiammazione Risposta protettiva volta a eliminare gli stimoli nocivi (patogeni, cellule danneggiate, sostanze irritanti) e avviare il processo di riparazione tissutale. Richiamo di proteine e leucociti circolanti nei tessuti, dove vengono attivati per eliminare i microbi. Difese antivirali Attivazione sistema immunitario adattativo

3 Cellular components of the innate immune system Neutrophils Macrophages Dendritic cells Natural Killer (NK) cells Innate Lymphoid Cells (ILCs) NKT, gd T cells Mast cells

4 Neutrophils Polymorphonuclear phagocyte = multilobed nucleus, and cytoplasmic granules. 2 types of granules: 1. specific granules: lysozyme, collagenase, and elastase. 2. azurophilic granules: lysosomes containing enzymes and other microbicidal substances, including defensins and cathelicidins. Production for human adult: > neutrophils / day Blood Circulation: few hours or days. Neutrophils migrate to sites of infection within a few hours after the entry of microbes.

5 Chemiotassi

6 Mononuclear Phagocytes Blood monocyte Tissue activated macrophage Macrophages respond to microbes as rapidly as neutrophils do, but macrophages survive much longer at sites of inflammation. Macrophages are the dominant effector cells of the later stages of the innate immune response, 1 or 2 days after infection.

7 Effector functions of macrophages Type II interferon

8 I macrofagi esprimono recettori che stimolano la fagocitosi + Fc receptors

9 Phagocytosis and destruction of microbes ROS: Reactive Oxygen Species NO: Nitric oxide Elastase Cathepsin G

10 Fagocitosi

11 Fagocitosi

12 Dendritic cells widely distributed in lymphoid tissues, mucosal epithelium, and organ parenchyma phagocytic capabilities express pattern recognition receptors (PRRs) and respond to microbes by secreting cytokines important roles in innate responses to infections and in linking innate and adaptive immune responses (critical function in adaptive immune responses by capturing and displaying microbial antigens to T lymphocytes)

13 Maturation of dendritic cells Conventional Potent antiviral activities In inflamed tissues

14 Conventional (cdc) and plasmacytoid (pdc) TLR3, 7, 8, 9 IFNa, IFNb DCs are different from Follicular Dendritic Cells (FDCs)

15 Conventional (cdc) and plasmacytoid (pdc) DCs are different from Follicular Dendritic Cells (FDCs)

16 Natural killer (NK) cells Lymphoid lineage 5% to 15% of these mononuclear cells in the blood and spleen and are rare in other lymphoid organs but concentrated in liver and gravid uterus Recognize infected and/or injured cells Respond by directly killing these cells and by secreting inflammatory cytokines

17 Functions of activating and inhibitory receptors of NK cells PTK = protein tyrosine kinase PTP = protein tyrosine phosphatase

18 KIR = Killer cell Immunoglobulin (Ig) - like Receptors NK receptors ADCC = Antibody Dependent Cellular Cytotoxicity LIR = Lymphocyte Immunoglobulin (Ig) - like Receptors ITAM/ITIM = immunoreceptor tyrosine based activation /inhibition motif LIR C type Lectin MHC class I

19 NK functions: cell-mediated cytotoxicity NK activation = granule exocytosis (perforin, granzymes) Expansion and activities of NK stimulated by cytokines IL-12, IL-15, IL- 18 and IFN (type I).

20 Il gruppo ILC1 comprende le cellule NK Cellule linfoidi innate (ILC)

21 Cellule NKT e T gd Abbondante nei tessuti epiteliali, quale l apparato gastrointestinale: difesa precoce contro i microbi Recettori con diversificazione limitata Riconoscimento -non ristretto a MHC- di antigeni di natura non proteica Producono citochine: IL-4, IFN-g and IL-17 (gd T)

22 Mastociti Presenti nella cute e nell epitelio delle mucose Esprimono TLRs (TLR-1, -2, -4, -6) Secernono rapidamente Citochine proinfiammatorie (TNF) Mediatori lipidici (prostaglandine, leucotrieni) e amine vasoattive (istamina) che determinano vasodilatazione e aumento della permeabilità capillare Enzimi proteolitici che possono uccidere i batteri e inattivare le tossine

23 Innate immunity components

24 Cytokines of the innate immune system Recruit, activate leukocytes and produce systemic alterations = increases in the synthesis of effector cells and proteins that potentiate antimicrobial responses. Principal sources : macrophages, neutrophils, NK cells, but also endothelial cells and some epithelial cells such as keratinocytes. As in adaptive immunity, cytokines serve to communicate information among inflammatory cells and between inflammatory cells and responsive tissue cells, such as vascular endothelial cells

25 Chemokines Around 50 chemokines, 8 to 12 kda polypeptides Number and location of N-terminal cysteine residues = classification into four families: CXC (also called a) CC (also called b) C CX 3 C CXC chemokines with ELR motif (glutamic acid-leucinearginine before the 1st C) mediate recruitment of neutrophils. The other CXC and CC chemokines recruit monocytes and lymphocytes, and other leukocytes.

26 Chemokines 2 main classes: CXC and CC 10 distinct receptors for CC, 6 distinct receptors for CXC, 1 for CX 3 C

27 Chemokines

28 Seven-transmembrane, GTP-binding (G) protein-coupled receptor GPCR superfamily Three subunits: Ga, Gb and Gg Chemokine receptors Resting cell: receptor associated G protein is inactive and GDP is bound to a subunit Ligand binding induces conformational changes resulting in replacement of GDP with GTP Active complex dissociates: a subunit and a complex of gb; each of these components can interact with downstream targets: Phospholipase C giving rise to IP3 Calcium Regulators of Ras-family GTPases Chemokine G receptors stimulate cytoskeletal changes and polymerization of actin and myosin, resulting in cell motility

29 Trasmissione segnale recettori chemochine

30 Adhesion molecules: selectins (slex) Carbohydrates present on glycoproteins L-selectin (CD62L) Neutrophils Monocytes Naive T/B cells Sialyl-Lewis X / PNAd on GlyCAM-1, CD34, MadCAM-1

31 Adhesion molecules: integrins Heterodimeric cell surface protein >30 different types Same structure: a/b One of 15 types of a chains One of the 7 types of b chains Cytoplasmic domains interact with cytoskeletal components (actin, vinculin, ) Chemokines after binding to chemokine receptors on leukocytes, activate integrins and mediate the increase in affinity of integrins

32 Adhesion molecules LAD: Leukocyte Adhesion Deficiency, defect in CD18 (b2 chain) (CD49aCD29)

33 Leukocyte recruitment Blood vessel lumen CXCL1, CXCL8, CCL2 3 4 diapedesis 2 Tissue Macrophages encounter microbes, produce cytokines (TNF, IL-1) that 2- activate the endothelium to produce selectins, ligands for integrins, and chemokines. 3- Selectins mediate rolling of blood leukocytes; 4- chemokines increase the affinity of leukocyte integrins which mediate firm adhesion and 5- stimulate the migration of the leukocytes through the endothelium to the site of infection.

34 Rotolamento

35 Adesione e rotolamento

36 Stravaso

37 Leukocyte recruitment

38 Leukocyte recruitment and homing Delivery of leukocytes of myeloid lineage (neutrophils and monocytes) from their bone marrow site of maturation into tissue sites of infection or injury Delivery of lymphocytes from their site of maturation (bone marrow or thymus) to secondary lymphoid organs To tissues : homing From blood: recruitment Delivery of effector lymphocytes from the secondary lymphoid organs in which they were produced to sites of infection in any tissue

39 T lymphocyte recirculation L-selectin ligands are peripheral node addressins (PNAd) displayed by sialomucins called GlyCAM-1 and CD34

40 Migration of naive and effector T cells

41 Migration of naive and effector T cells

42 Lymphocyte traffick CCL19 = MIP3b GlyCAM-1= L-selectin ligand

43 Egress of T cells from lymphoid organs requires S1PR1 Fingolimod, immunosuppressive drug, is an agonist of S1PR1: sphingosine 1- phosphate receptor 1, and causes its downregulation

44 Stimulation of adaptive immunity by innate immune responses Signal 1 = non self Signal 2 = danger

45

46 Type I interferons are antiviral proteins produced by cells in response to viral infection Induce chemokines to recruit lymphocytes

47 Cellule dendritiche

48 Produzione di proteine di fase acuta Acute-phase proteins TNF, IL-1

49 Roles of cytokines in innate immunity

50 NK cells are an early component of the host response to virus infection