Innate Immunity

1. Innate Immunity

4. Cellular Innate Immunity

5. Cells Involved in the Innate Immune System • Polymorphonuclear Leukocytes “PMNLS”, “granulocytes”. • Basophils • Mast cells • Eosinophils • Neutrophils • Monocyte and macrophage • Innate lymphoid cells • Mast cell • Dendritic cell

6. Cells Involved in the Innate Immune System • They contain the enzyme – rich lysosomes. • They produce peroxide and superoxide radicals which are toxic to many microorganisms • Some lysosomes contain bactericidal proteins, such as lactoferrin. • Defects in PMN cell function are accompanied by chronic or recurrent infection • Some of them have a major role in antigen detection and presenting

8. Phagocytes • Neutrophils • Neutrophils are produced at a rate of 7 million per minute and released from bone marrow. • They are short –lived “2-3 days” • They represent 95% of the circulating granulocytes.

9. Neutrophils are the first white blood cells recruited to sites of acute inflammation, in response to chemotactic cues such as CXCL8 (interleukin-8, IL-8) produced by stressed tissue cells and tissue-resident immune cells such as macrophages. • Neutrophils therefore comprise a large proportion of the early cellular infiltrate in inflamed tissues and are the major constituent of pus.

11. They contain antibiotic proteins which are stored in two main types of granules: 1- The primary “azurophilic “ granules, they are lysosomes containing acid hydrolases ,myeloperoxidase,lysozyme, defensins and bacterial permeability inducing protein”BPI”. 2- The secondary granules “ specific to neutrophils” contain lactoferrin and lysozyme. • Other small granules contain gelatinase • Neutrophils can also release granules and cytotoxic substances extracellularly when they are activated by immune complexes through their Fc receptors.

12. Neutrophil under Electron Microscope

13. Macrophages: They are phagocytes derived from blood monocytes. Have different names: • Kupffer cells, in the liver. • Alveolar macrophages, in the lung. • Splenic macrophages, in the white plup. • Peritoneal macrophages, free floating in peritoneal fluid. • Microglial cells, in the central nervous system.

15. Two main pathways of macrophage: reverse action

17. Endocytosis • It is the ingestion of macromolecules present in extra cellular tissue fluid. • This occurs either by nonspecific membrane invagination or by receptor mediated endocytosis with endocytic vesicle – endosome- lysosomes yield breakdown products.

18. Phagocytosis • The ingestion of invading particles e.g. bacteria – by phagocytic cells. • Phagocytosis is aided by opsonins “antibodies, complement components”. • The foreign particle is entrapped in a phagocytic vacuole.

20. H2 O2 + Cl- myeloperoxidase OCl- + H2O 1O2-+Cl-+ H2O 2OCL- + H2O 2O2- + 2H+ Superoxide dismutase H2O2 + O2- 2 H2 O2 catalase H2O + O2- Intracellular killing • Oxygen dependent • Myeloperoxidase dependent

21. Glucose +NADP+ G-6-P-dehydrogenase Pentose-P + NADPH NADPH + O2 Cytochrome b558 NADP++ O2- 2O2- + 2H+ Superoxide dismutase H2O2 + 1O2 2O2- + H2O2 .OH + OH- + 1O2 • Oxygen dependent • Myeloperoxidase independent • Oxygen independent

24. Innate lymphoid cells (ILCs) • are a group of innate immune cells that belong to the lymphoid lineage but do not respond in an antigen-specific manner, as they lack a B or T cell receptor. • ILCs do not express myeloid or dendritic cell markers. • Classified at the first time in 2013 according to transcriptional factors and cytokine release into three groups : Group 1 ILCs or ILCs1 : • can produce type 1 cytokines (notably IFNγ and TNF) and comprise NK cells and ILC1s. • analogous to Th1 and cytotoxic T cells (tumor and viral clearance). • ILC1s are weakly cytotoxic cells closely related to ILC3s . • Raise Natural killer ('NK') cells 

25. Group 2 ILCs • Can produce type 2 cytokines (e.g. IL-4, IL-5, IL-9, IL-13). • Also termed natural helper cells, nuocytes, or innate helper 2 cells . • analogous to Th2 cells ( helminthic infection). Group 3 ILCs • defined by their capacity to produce cytokines IL-17A and/or IL-22 . • Raise Lymphoid tissue inducer ('LTi') cells  essential for development of lymphoid organs during embryogenesis and after birth • analogous to Th17 cells (Enteric pathogens clearance, lymphoid tissue development, memory T cells maintenance)

26. Spits, et al., 2013

28. Dendritic cells • Long lived, reside in an immature state in most tissues • They recognize and phagocytize pathogens and other antigens. • They are found as inter digitating cells of the thymus and Langerhans cells in the skin. • They are derived from the same hematopoietic precursor cells as monocytes. • Direct contact with many pathogens leads to the maturation of dendritic cells and increasing their antigen presenting capacity such maturation allows them to activate naïve antigen specific T-cells. Thus they are important in both innate immunity and the initiation of adaptive immune responses.

30. Natural killer cells : • a lymphocyte able to bind to certain tumour cells and virus-infected cells without the stimulation of antigens, and kill them by the insertion of granules containing perforin • They lack TCRs • NK cells express non – TCR – related receptors called killer cell inhibitory receptors (KIR) which bind to MHC class I molecules. • Killing is achieved by the release of various cytotoxic molecules, some of these cause the pore formation on the membrane of target cells, leading to its lysis, other molecules enter the target cell and cause apoptosis.

31. Functions • Killing infectedcells (cytotoxic) • Secretion of cytokines • Activation by • Type 1 interferons • Infectedcells • Stimulatescytotoxicfunction • IL-12 and TNF-alpha • Macrophages • Stimulates cytokine secretion

32. Functions of NK cells

34. Activated NK cells release IFN-gamma and IL-12 which activates macrophages Differentiate infected from uninfected cells NK cells express receptors for MHC class I molecules Binding of NK cells to MHC class I molecules turn off NK cells NK cells provide innate immunity to intracellular pathogens NK cells vs NKT cells NKT cells are NOT the same as NK cells. NKT cells are T cells with an αβ TCR. However, they also express some of the cell-surface molecules of NK cells — hence their name

37. Functions of activating and inhibitory receptors of NK cells

38. So how all these cells recognize different antigens??

39. Pattern recognition receptors (PRRs) • The interaction with the pathogen can be direct by pattern recognition receptors (PRRs), or indirect, through recognition of opsonised microbes by Fc receptors or complement receptors. • PRRs play a crucial role in the proper function of the innate immune system. • PRRs are germline-encoded host sensors, which detect molecules typical for the pathogens. • They are proteins expressed, mainly, by cells of the innate immune system, such as dendritic cells, macrophages, monocytes, neutrophils and epithelial cells.

40. Pattern recognition receptors (PRRs) • PRR identify two classes of molecules:  • Pathogen-associated molecular patterns (PAMPs), which are associated with microbial pathogens. • Damage-associated molecular patterns (DAMPs), which are associated with components of host's cells that are released during cell damage or death. • They are also called primitive pattern recognition receptors because they evolved before other parts of the immune system, particularly before adaptive immunity. • PRRs also mediate the initiation of antigen-specific adaptive immune response and release of inflammatory cytokines.

42. PRRs devided into three classes : • Membrane-bound PRRs : • Receptor kinases • Toll-like receptors (TLR) • C-type lectin Receptors (CLR) • Cytoplasmic PRRs : multifunctional! ! • DS viral DNA, gram negative peptedoglycan, apoptosis … • Secreted PRRs : • Complement receptors, collectins (as MBL), pentraxins (as CRP)

43. Toll – like receptors "TLRs": • Each recognizes specific microbial components. Activation of TLRs by microbial components leads to activation of the innate immunity as well as adaptive immunity through production of cytokines and expression of co simulators molecules. • Toll-like receptors (TLRs) are a class of proteins that play a key role in the innate immune system. They are single, membrane-spanning, non-catalytic receptors usually expressed on many immune cells to recognize structurally conserved molecules derived from microbes. Once these microbes have reached physical barriers such as the skin or intestinal tract mucosa, they are recognized by TLRs, which activate immune cell responses. The TLRs include TLR1, TLR2, TLR3, TLR4, TLR5, TLR6, TLR7, TLR8, TLR9, TLR10, TLR11, TLR12, and TLR13, though the latter three are not found in humans. • TLR's received their name from their similarity to the protein coded by the toll gene identified in Drosophila.

45. TLRs: location and target

46. Different TLRs can recognize different antigens as listed below • TLR-1:- Bacterial lipoprotein and peptidoglycans • TLR-2:- Bacterial peptidoglycans • TLR-3:- Double stranded RNA • TLR-4:- Lipopolysaccharides • TLR-5:- Bacterial flagella • TLR-6:- Bacterial lipoprotein • TLR-7:- Single stranded RNA • TLR-8:- Single stranded RNA • TLR-9:- CpG DNA • TLR-10:- Unknown

48. Recognition of microbes and damaged self by the innate immune system

49. Cellular location of pattern recognition molecules of the innate immune system

50. TLRs are essential for innate cell specificity in infection fighting. Example: neutrophils have no TLR3 so they are not efficient in fighting dsRNA viruses.