IMMUNOLOGY Sherko A Omer MB ChB, MSc., PhD
Basic immunology • Clinical immunology • Diagnostic immunology • Handout notes • PowerPoint slides • References
WHY IMMUNOLOGY ? Pathology ..infection, allergy, autoimmune disorders Protection…. immunisation, tumour Diagnosis …Many fields….. Treatment …..allergic disorders,
DEFINITIONS Immunology …..the science Immunity .. state of protection against microorganisms, toxic molecules and foreign cells Immunisation … induction of immunity
TYPES OF IMMUNITY 1. Innate (natural, nonspecific) immunity 2. Adaptive (acquired, specific) immunity
TYPES OF IMMUNITY InnateAdaptive Specificity Nonspecific Specific Memory No Yes Time-dependency No? Yes? Self/nonself No Yes
TYPES OF ADAPTIVE IMMUNITY 1. Active immunity… Body made e.g after infection or active immunization 2. Passive immunity … Not made by host e.g maternal immune transfer to the baby or passive immunisation
ORGANISATION OF IMMUNE SYSTEM 1. Organs lymphoid organs such as thymus, spleen and lymph nodes 2. Tissues lymphoid tissues such MALT 3. Cells lymphoid cells such as T cell, B cell, NK cells. Other cells such as macrophage, neutrophils, 4. Proteins and peptides such as complement system and cytokines
CELLS OF THE ADAPTIVE IMMUNE SYSTEM 1. Lymphoid cells …T lymphocytes, B lymphocyte, NK cells. 2. The mononuclear phagocyte system cells. 3. Cells involved in the inflammatory phase of immune response (Neutrophils, Basophils)…
Hematopoietic and immune cell differentiation
CLUSTER OF DIFFERENTIATION(CD) Lymphocytes, leukocytes and other body cells express a large number of different macromolecules on their surfaces; these macromolecules can be identified using monoclonal antibodies (mAb) that bind them. Theses macromolecules can serve either as surface determinants specific to a particular cell type or subpopulation (markers) or they serve as receptors. http://prow.nci.nih.gov/
T cell-APC interaction at molecular level
LYMPHOID CELLS Lymphocytes are the predominant cells of immune system. Lymphoid cells makes 20% of total white blood cell count and they are characterize by having a long life span, their plasma membrane shows slow amoebic movements. Naive lymphocytes, cells that have not previously been stimulated by antigens, are called small lymphocytes by morphologists.
LYMPHOID CELLS Main types of lymphocytes include: T lymphocytes B lymphocytes Natural killer cells (NK cells) Other cells, LAK
T LYMPHOCYTES or T CELLS Lymphocytes arise from maturation of steam cells in thymus are called T (Thymus) lymphocytes. In thymus, there is rearrangement and reproductive expression of TCR (T cell receptors) genes and selection of some antigen receptors that permits mature T cells to recognize antigens.
T LYMPHOCYTES or T CELLS Development of CD4+ and CD8+ T cells in the thymus
T LYMPHOCYTES or T CELLS T lymphocytes accounts for: 65-75% of blood lymphocytes More than 95% of thymus lymphocytes 70-80% of lymph node lymphocytes 20-30% of spleen lymphocytes.
T LYMPHOCYTES or T CELLS T cells that express CD4 are generally referred to as T helper (TH) lymphocytes. T cells that express CD8 are called T Cytotoxic Cells (Tc). Both CD4 and CD8 cells can act as cytotoxic T lymphocytes (CTL), depending on whether class II or class I MHC is recognized, respectively. A subset of T lymphocyte act as suppressor or regulatory cell T reg.
T HELPER SUBSETS TH can be subdivided into two categories, depending on their function, response to various cytokines, and their ability to secrete cytokines TH1 and TH2. TH cells start as precursor cells that make IL-2. On initial stimulation, these cells develop into TH0 cells, which can secrete several cytokines, including IFN-, IL-2, IL-4, IL-5, and IL-10.
T HELPER SUBSETS TH0 cells can develop into either TH1 or TH2 cells, with IFN- and IL-12 favouring the development of TH1 and IL-4 and IL-10 favouring the development of TH2. TH1 cells secrete IFN-, whereas TH2 cells secrete IL-4, although both secrete several other cytokines (IL-3, GM-CSF, TNF-) equally well. TH1 favours the promotion of cellular immunity, whereas TH2 favours the promotion of humoral immunity.
T CELL SURFACE MARKERS CD2 which serve as receptor for sheep red blood corpuscles, mixing T lymphocytes with sheep RBCs results in formation of a rosette. CD3 a hetropolymer that consists from 5 polypeptides, CD3 play no role in antigen recognition but it involves in intracellular signalling to initiate a series of intracellular reaction. CD5 present on all T lymphocytes and some B lymphocytes.
T CELL SURFACE MARKERS conti. T lymphocytes that carry CD4 molecules called CD4+ or TH (helper). T lymphocytes that carry CD8 molecules called CD8+ or TC (cytotoxic). CD28, a receptor for the co-stimulatory B7 family of molecules present on B cells and other antigen presenting cells is present on mature T cells. CD45, a signal-transduction molecule present on mature T cells.
T CELL SURFACE MARKERS conti. T cell Receptor (TCR), these are antigen recognizing molecules on T lymphocytes, each TCR is a heterodimer that consist from two non identical polypeptides. Two types of TCRs are exist; TCR which compose from chain and it is present in 5% of T lymphocytes and TCR which compose from chain and present in 95% of T lymphocytes. TCRs are associated with CD3 so there is either CD3/ or CD3/.
T CELL SURFACE MARKERS conti. Development of αβ and γδ T cells from lymphocyte stem cells (LSC). Two types of T cells are produced in the thymus with different TCRs (αβ and γδ). The classical T cells (Th and Tc) utilize αβ for their TCR.
T CELL FUNCTIONS T lymphocytes can recognize antigens through their TCR/CD3 complex and this recognition is achieved in CD4+ cells when the antigen is recognized in association with class II MHC while CD8+ cells can recognize antigen in association with class I MHC. CD4+ can help both B cells and CD8+ cells in immune response, it may also perform cytotoxicity while CD8+ cells perform cytotoxicity against virally infected cells, tumour and allograft cells .
T CELL FUNCTIONS conti. Activation of TH cells leads to production of cytokines like: IL-2 (Interleukin 2), serves as independent polyclonal proliferation factor for other T cells, TC/S and NK cells. IL-4, augments B cells and induce expression of Fc receptors on B cells. IL-3, -5, -10 and -12. GM-CSF. IFN (Gamma interferon). TNF (Tumour necrosis factor).
B LYMPHOCYTES or B CELLS B lymphocytes arise from stem cells that migrate to foetal liver and latter to bone marrow where there is gene rearrangement and establishment of B cells specific antigen receptors (mIg) and expression of several markers. B lymphocytes after were called after the Bursa of Fabricious which is a lymphoepithelial organ near the cloaca of birds.
B LYMPHOCYTES or B CELLS • B lymphocytes accounts for : • 5-10% of blood lymphocytes • Less than 15% of thymus lymphocytes • 10-20% of lymph node lymphocytes • 40-50% of spleen lymphocytes
B CELL SURFACE MARKERS Membrane-bund Immunoglobulins (mIg), these are monomeric surface IgM, IgD and to less extend surface IgG, IgA or IgE, the mIg serve as antigen receptors (like TCR on T lymphocytes), mIg can be detected by using fluorescent labelled anti-human Immunoglobulin. CD32, receptors for Fc portion of Immunoglobulin. CD19, CD20
B CELL SURFACE MARKERS conti. CD5, present on some B lymphocytes (in some autoimmune disorders) CD35 which is a complement receptor (CR1) for C3b CD21 which is a complement receptor (CR2) for C3d and EB virus CD40 Receptor for transferrin Class II MHC
B CELL FUNCTIONS Activation of these cells by specific antigen is achieved when the antigen binds to the mIg of B cells, this process may be helped by T cells or not, activation results in several intracellular chemical reactions and results in clonal expansion of B cells and development of either long lived memory cells or plasma cells. Some B lymphocytes may serve as antigen presenting cells APCs so they present antigens to T cells.
PLASMA CELLS Cells that arise from B lymphocytes, they have an eccentric nucleus with large amount of basophilic cytoplasm (RNA). Each plasma cell produce and secrets one type of Immunoglobulin so plasma cells are antibody producing and secreting cells.
NATURAL KILLER CELLS or NK CELLS These cells lack antigen receptors (TCR or mIg) so different from both T and B cells. Most NK cells appears as Large Granular Lymphocytes (LGLs) or third population cells (TPCs), they are larger than other lymphocytes.
NATURAL KILLER CELLS or NK CELLS NK cytoplasm contain azurophilic granules and eosinophic granules that stains for acid hydrolase. Morphology and surface marker of NK cells are intermediate between lymphocytes and monocytes and they account for 10-15 % of total blood lymphocytes or 1-2% of spleen lymphocytes. Morphology and surface marker of NK cells are intermediate between lymphocytes and monocytes and they account for 10-15 % of total blood lymphocytes or 1-2% of spleen lymphocytes.
NK CELL SURFACE MARKERS CD2 CD3 (CD3ζ) is present in minority of NK cells CD16 (Hum Fc R III) for IgG1 and IgG 3, present in majority of NK cells CD11b (CR3), CD11c (CR4) CD56 adhesion molecule
NK CELL FUNCTIONS NK cells are MHC-non restricted killer cells; they do not require sensitization (previous exposure )to express their killer functions As these cells have no specific receptors so they act as non specific cytotoxic cells (natural), they are specialized in killing virally infected cells, they have long been thought to be important in tumor surveillance because they can kill some tumor cells as most tumors lack MHC expression.
NK CELL FUNCTIONS conti. NK cells can kill also through ADCC (Antibody Dependant Cell Cytotoxicity) when they carry cytotoxicity on antibody coated cells. Production of cytokines such as IL-2, TNF-, IFN- and GM-CSF. By secreting IFN-, NK cells can influence the adaptive immune system by favouring the differentiation of TH1 and inhibiting the differentiation of TH2.
MONOCYTE MACROPHAGE SYSTEM CELLS Steam cells that pass to bone marrow and under the effect of IL-3, GM-CSF and M-CSF develop to monocytes and latter differentiates to different macrophages. The series involve many cells: In Bone marrow monoblast, promonocyte and monocyte In blood, monocytes are present; they circulate for few days then migrate to tissues.
MONOCYTE MACROPHAGE SYSTEM CELLS • In Tissue monocytes differentiate in to resident macrophages staying in tissues: • Histiocytes… Connective tissue • Histiocytes, Langerhans‘….skin • Kupffercells…..liver • Alveolar and tissuemacrophages…. lungs
MONOCYTE MACROPHAGE SYSTEM CELLS • Microglialcells, CSF macrophages..CNS • Red pulp macrophages…spleen • Free or fixed macrophages, Interdigitatingcells...lymph nodes • Oseoclast….bone • Mesangial cells….kidney • Macrophages….bone marrow, MALT, thymus, and endocrine glands
MONOCYTE MACROPHAGE SURFACE MARKER • Class II HLA (HLA - DR, -DP, and -DQ) • Complement receptors for C3: CR1 (CD 35), CR3 (CD11 b), CR4 (CD 11C) • Fc receptors like Hum Fc RI(CD 64), HuFc RII (CD32) • Monocyte specific antigen CD14 • CD4 is present on monocytes • On macrophages HumFc RIII (CD 16) are present
MONOCYTE MACROPHAGE FUNCTIONS Phagocytosis both by non specific mechanisms or specific mechanisms (immune). They can ingest many microorganisms and digest them through oxygenindependent mechanisms or oxygen dependent intracellular killing. These cells can act as APCs as they are rich in class II MHC.