Macrophages, T and B cells, primary and secondary immune organs, mucosal immune system

1. Macrophages, T and B cells, primary and secondary immune organs, mucosal immune system

2. Macrophages • Terminal stage of monocyte-macrophage line differentiation • Monocyte-macrophage cells differentiate from myeloid precursor (developed from pluripotent stem cell bearing CD34) in bone marrow • Matured monocytes are released to peripheral blood stream, then move in organs and develop into tissue macrophages

4. Development of monocytes and macrophages is affected by various cytokines: • SCF(stem cell factor): produced by stromal cells → activation of stem cell • GM-CSF (granulocyte-monocyte colony stimulating factor): produced by bone marrow (BM) stromal cells, lymphocytes → stimulation of monocyte production • M-CSF (monocyte colony stimulating factor): produced by stromal cells, lymphocytes, endothelial and epithelial cells → production and maturation of monocytes • IL-3: produced by lymphocytes → production of monocytes (and other blood cells)

5. Macrophages- development • Monocytes- in the blood (7%) and the rest in bone marrow • Macrophages - in tissues

6. histiocytes

7. Macrophages • a monocyte enter damaged tissue through the endothelium of a blood vessel • a monocyte is attracted to damaged site by chemokines, triggered by stimuli including damaged cells, pathogens and cytokines released by macrophages • after migration of monocytes to the tissues, they differentiate into different forms of macrophages • macrophages survive several months

8. Macrophage surface molecules • MHC gp I, II assist in the presentation of antigen to T lymphocytes • CD 35 - complement receptor 1 (CR 1), binds complement C3b • Receptor for the Fc portion of IgG • CD 14 - receptor for bacterial lipopolysaccharides

9. Cytokines produced by macrophages IL- 1 α, ß - stimulate both T and B cells, Ig synthesis, activation of other macrophages, sensitizing cells to IL-2 and IFN TNF- α - similar in function to IL-1 IL- 8 - secreted by activated macrophages - chemokine attracting neutrophils and T cells IL-12 - promotes induction of Th1 cells, inhibits Th2 cells IFN- α- activates host cells to induce enzymes inhibiting viral replication; increases expression of MHC gp I on host cells; activates NK cells, T cells, other macrophages

10. Functions of macrophages • Phagocytosis • Production of cytokines • Presentation of epitops with MHC gp II • Presentation of epitops with MHC gp I

11. Phagocytosis • a foreign substances are ingested • microbes are killed and digested • follows processing of antigenic epitopes and their presentation on the cell membrane

12. Macrophage - functions • Macrophages provide defense against tumor cells and human cells infected with fungi or parasites. • T cell becomes an activated effector cell after recognition of an antigen on the surface of theAPC → release chemical mediators → stimulation of macrophages

14. Presentation of epitopes with MHC gp II • After endocytosis and degradation of the antigen, presentation of its epitopes follows • epitope is connected to MHC gp II → cell surface → presentation to Th cells • MHC (Major Histocompatibility Complex) = complex of genes that governs the production of the major histocompatibility antigens - in humans termed HLAs (Human Leukocyte Antigens)

15. Presentation epitopes with MHC gp I • intracellular parasites are hydrolyzed in proteasomes of macrophages • their peptides are connected to TAP (Transporters Associated with antigen Processing molecules 1,2), that carry the epitope and MHC gp I → presentation on the cell surface to Tc cells

16. Antigen presentation

17. Dendritic Cells (DC) • DC mature after a contact with pathogen, then migrate to lymph nodes where antigen-specific immune response develops • DC are equipped with numerous cytoplasmic processes, allowing contact with up to 3000 T cells • In lymph nodes, the expression of MHC gp I and co-stimulatory molecules (CD80, CD86) on DC increases

18. Types of Dendritic Cells • Myeloid DC – similar to monocytes – give rise to Langerhans cells (epidermis), interticial DC (lymph nodes) • Lymphoid DC – give rise to plasmocytoid DC - looks like plasma cells, but have certain characteristics similar to myeloid cells, they produce huge amounts of interferons

19. Function of DCs • DCs are the most important APC • DCs can be easily infected by viruses → processing of viral proteins → their presentation in complex with MHC gp I → activation of Tc • DCs can ingest extracellular viral particles → their presentation in complex with MHC gp II → activation of Th2 cells → help for B cells → production of antiviral antibodies • DCs can also be activated by apoptotic cells

20. Antigen Presenting Cells (APC) Dendritic cells, macrophages, B cells Antigen processing and its presentation to T cells in the complex with HLA class I or II Providing additional signals to T cells which are necessary for their activation (CD 80, CD 86)

21. T cells: ontogenesis, surface markers. Subpopulations of T cells and their functions.

22. T lymphocytes - ontogenesis • Stem cell in BM gives rise to lymphoid precursor cell which matures into 3 types of lymphocytes: • T lymphocytes • B lymphocytes • Natural killer (NK) cells • Pro-thymocytes move to the thymus where continue the maturation into T lymphocytes • Maturation of B lymphocytes continues in BM

24. Surface markers of T cells • CD (Cluster of Differentiation) proteins - molecules on the cells membrane, they allow the identification of cells • TCR- receptor for antigen • MHC gp I

25. CD proteins • allow an identification of T-cell subsets • CD 2 = adhesion molecule • CD 3 = important in intracellular signaling (initiation of immune response); closely associated with TCR • CD 5,7 • CD 4,8 = are expresed on subclasses of mature T cells; CD4 reacts with MHC gp II,CD8 reacts with MHC gp I on macrophages • CD 28 – molecule that provides co-stimulatory signals, binds CD80 and 86

26. Maturation of T lymphocytes Consist of three types of processes: • Proliferation of immature cells • Expression of antigen receptors genes • Selection of lymphocytes

27. TCR • Antigen receptors are encoded by several gene segments that recombine during lymphocyte maturation • Heterodimer consisting of 2 nonidentical polypeptide chains linked together by disulfide bonds • > 95% T cells express the αß heterodimer, 5% γδ • TCR heterodimer is noncovalently associated with the γ,δ,ε chains of the CD3 molecule • complex TCR-CD3 makes contact with both the Ag and MHC gp

29. Subpopulation of T cells • Subpopulation of T cells are defined according to their particular function and their CD membrane markers • T cytotoxic cells (Tc) CD8+ - recognize the foreign epitope in association with class I MHC molecules • T helper cells (Th) CD4+ - recognize the epitopes in association with class II MHC molecules

30. T cytotoxic lymphocytes (Tc;CD8+) • cause lysis of target cell; active against tumors, virus-infected cells, transplanted allogeneic tissue • release TNF → decrease of proteosynthesis • recognize the foreign epitope in association with MHCgp I molecules • Destroy target cells by perforins (create pores in the cell membrane → cell lysis) and granzymes (degradation of essential macromolecules)

31. T helper lymphocytes(Th; CD4+) • recognize the epitopes in association with MHC gp II • help for B cells to produce antibodies and help for phagocytes to destroy ingested microbes • subsets of Th cells: Th1, Th2 cells

32. Regulatory T cells • Express CD4, CD25, FoxP3 • Regulate the activation or effector function of other T cells • Are necessary to maintain tolerance to self antigens • Production of IL-10, TGF-b

33. The role of thymus. Positive and negative selection of Tlymphocytes.

34. The role of thymus • In thymus, lymphocyte precursors from the bone marrow become thymocytes, and subsequently mature into T cells • Once matured, T cells migrate from the thymus and constitute the peripheral T cell repertoire responsible for specific cell response

35. Phases of thymocyte maturation • A rare population of hematopoietic progenitors enters the thymus from the blood, and expands to a large population of immature thymocytes • Immature thymocytes each produce distinct T cell receptors by a process of gene rearrangement. • This process is error-prone, and some thymocytes fail to make functional T cell receptors, whereas other thymocytes make T cell receptors that are autoreactive

36. Positive and negative selection • Immature thymocytes undergo a process of selection, based on the specificity of their T cell receptors. • This involves selection of T cells that are functional (positive selection), and elimination of T cells that are autoreactive (negative selection)

37. Positive selection of T cells • Entrance of precursor T cells into thymus from the blood • Presentation of self-antigens in complexes with MHC molecules on the surface of cortical epithelial cells to thymocytes • Only those thymocytes which bind the MHC/antigen complex with adequate affinity will receive a vital "survival signal" • The other thymocytes die (>95%)

38. Negative selection of T cells • Thymocytes that survive negative selection migrate towards the thymic cortex and medulla • Presentation of self-antigen in complex with MHC molecules on antigen-presenting cells • Thymocytes that react inappropriately strongly with the antigen receive an signal of apoptosis

39. B-lymphocytes - ontogenesis, surface markers, function.

40. B-lymphocytes are an essential component of the adaptive immune system • Maturation of B cells takes place in BM • B cell originates from stem cell and need to be in touch with the stromal cells in the bone marrow • Stromal cells produce SCF (stem cell factor) necessary for development at early period, IL-7 necessary at later period of maturation • Ig gene rearrangements and the appearance of surface markers identify the stage of B-cell development

41. Development of B lymphocytes • Lymphoid progenitor → pro-B cells • During maturation from pro-B cells into pre-B cells: Ig genes of the heavy chain recombine; pre-B cells express pre-BCR • During maturation from pre-B cells into B cells: Ig genes of the light chain recombine • Immature B cells express membrane IgM • Mature B cells express membrane IgM and IgD = BCR and are able to respond to antigen in peripheral lymphoid tissues

42. Negative selection • If an immature B cell binds an antigen in the bone marrow with high affinity → further maturation is stopped and B cell dies by apoptosis • Negative selection eliminates potentially dangerous cells that can recognize and react against self antigens • B cells that survive this selection process leave the bone marrow through efferent blood vessels

43. B-lymphocytes – surface markers • CD 10 - immature B cells, malignant cells • CD 35 - receptor for the C3b of the complement • CD 19 - characteristic marker of B cells • CD 20 - typical surface antigen of Ig-positive B lymphocytes • IgM, IgD - antigen receptors = BCR • MHC gp II - antigen-presenting molecules

44. B-lymphocytes – functions • After stimulation B lymfocytes convert into the plasma cells and produce antibodies against soluble antigens • Other functions are : antigen presentation cooperation with complement system

45. Primary immune organs and their role in the immune system.

46. Primary immune organs • Bone marrow • Thymus • are organs of development, differentiation and maturation of immune cells and elimination of autoreactive cells • T and B lymphocytes mature and become competent to respond to antigens in PIOs

47. Bone marrow is the central cavity of bone and the site of generation of all circulating blood cells in adults, including immature lymphocytes, and the site of B-cell maturation. • The pluripotent stem cell gives rise to the progenitors of all immune cells • Production of the cells takes place in the spaces divided by vascular sinuses • Endothelial cells of the sinuses produce cytokines • Sinuses are bordered byreticular cells

49. Differentiation in the BM • Differentiation from the stem cell is influenced by: • membrane interaction between the stem cells and the stromal cells • cytokines (CSF, IL-3, thrombopoetin, erythropoetin)

50. Thymus • is located between the sternum and the major vessel trunks • It consist of two lobes • Each lobe is surrounded by a capsule and is divided into lobules, which are separated from each other by strands of connective tissue = trabeculae