Immune Cells, Receptors & Markers Lecture 3 PDF

BASIC IMMUNOLOGY Immune Cells, Receptors & Markers Lecture-3 IMMUNOLOGY and MICROBIOLOGY UNIT Lymphoid tissues are classified as: 1- 2- Lymphoid Tissues & Organs Classification of White Blood Cells: Cells o...

BASIC IMMUNOLOGY Immune Cells, Receptors & Markers Lecture-3 IMMUNOLOGY and MICROBIOLOGY UNIT Lymphoid tissues are classified as: 1- 2- Lymphoid Tissues & Organs Classification of White Blood Cells: Cells of Myeloid Lineage: N o Granular leukocytes:  Neutrophils,  Eosinophils,  Basophils  Mast cells. o Agranular leukocytes:  Monocytes, macrophages & dendritic cells. Cells of Lymphoid Lineage: o Granular leukocytes: NK cell. o Agranular leukocytes: T cells and B cells. Cells of Myeloid lineage: A. Granular leukocytes: Neutrophils or polymorphonuclear cells: N ~60% of the peripheral blood leukocytes. Metamyelocyte, juvenile (band) form, stab form, and segmented (mature) form. Activated mainly in acute bacterial infection. Eosinophils: Eosin-loving granules, 0-5% of WBCs. Activated in helminths infection and in allergy. Basophils: Acidic cytoplasmic granules contain histamine. Form 0-1% of WBCs. Activated in allergic conditions. Mast Cells: Scattered in the connective tissues especially skin, mucosa and epithelia. Contains histamine. Activated in allergic conditions. From Granulocytic-myeloid cell B. Agranular leukocytes: Monocytes, macrophages & DC: Monocytes in circulation, macrophage and DC in tissues. 5-7% of peripheral blood leukocytes. N Antigen presenting cells (APC). Scavenger cells for innate immunity. - Macrophage markers: CD14, CD40, CD11b Cells of Lymphoid Lineage (Lymphocytes): Account for ≈ 40% of WBCs. Differ according to markers on cell surface called cluster of differentiation (CD): 1-Thymus-derived cells (T cells). 2-Bone marrow-derived cells (B cells). 3-Natural killer cells (NK cells). o Thymus-derived cells: T lymphocytes: Arise from the bone marrow and mature in the thymus, then enter the circulation Identified by presence of CD3 complex (TCR). Four subsets: o CD4⁺ T cells (helper): recognize MHC class II. o CD8⁺ T cells (cytotoxic): recognize MHC class I. o CD4+ and CD25+ T regulatory (Treg) o T suppressor (Ts) cells. Clonal Selection of T Lymphocytes: Double negative prothymocytes enter the thymus: they do not express CD4, or CD8 molecules, or TCR-CD3. They soon express TCR-CD3 complex, and both CD4 and CD8 (double positive cells; D.P). Positive Selection: D.P-Thymocytes die within 3-4 days unless they recognize and bind to major histocompatibility complex (MHC-I,II). (MHC I or II present on Cortical epithelial cell). Negative Selection: Positively selected T cells (CD4 or CD8) which bind strongly to self peptides of the MHC I or MHC II on medullary APCs (Phagocytes) undergo apoptotic death.  o Bone marrow-derived cells (B-Cells): N - Arise and mature within then the bone marrow. - Markers: - B cell receptors (antibodies: IgM & IgD) - CD19, CD20, & CD21(complement receptor). - Two types: - B1 present in respiratory &GIT systems. - B2 widely distributed in lymphoid organs and tissues. - Isotype switching is typical for B2 lineage. Plasma cells: - Terminally differentiated B cells. - Immunoglobulin producing cells. Plasma cell  B lymphocytes T lymphocytes Refers to Bone marrow-derived Thymus-derived Site of maturation Bone marrow Thymus Percent of total lymphocytes 10-15% 75-80% Surface markers CD19, CD20 CD3, CD4 or CD8 , CD21, & CD35. Antigen receptor BCR (IgM , IgD). TCR (α and β chains) MHC-II Nature of recognized antigen A wide variety of Protein only in the form of antigens; proteins, Peptide+MHC molecules on polysaccharides, lipids, the surface of APC nucleic acids Function Humoral immunity Cell-mediated immunity  o Natural killer cells (NK-Cells): N - Forms 5-10% of peripheral blood lymphocytes. - Lack B cell receptor. Surface markers: CD16, CD56 & Fc receptor for IgG. -Some NK cells carry TCR and, CD4 or CD8 markers. -Very active in killing virally infected cells and tumor cells. - Have two major receptors: o Killing activation receptor (KAR) o Killing inhibition receptor (KIR)  D-Natural killer cell receptors: N 1-Killer activation receptors (KARs): Recognize the presence of stress-related molecules expressed by the virally infected cell and tumor cell. 2-Killer inhibition receptors (KIRs): Recognize the presence of MHC class I, which is normally displayed on the host cell surfaces.  2-Somatically Generated Receptors: N A-T cell receptors (TCR): - Associated with cluster of differentiation 3 (CD3). - Binds to antigen-MHC. - CD4 and CD8 are co-receptors. B- B cell receptors (BCR): - Immunoglobulins IgM & IgD serve as B-cell receptors.  Reference: N Lippincott’s Immunology 2nd edition: -Chapter 4: Cells of Innate immune system: Pages 34-39. -Chapter 9: Clonal selection: Pages 114-117. B-Lymphocytes types: B-1, B-2: Page 120 -Chapter 2: Immune cell receptors: page 15-19 Lippincott’s Immunology 3rd edition.