Question

Which specific type of T cells is involved in the clonal selection of antibody-producing B cells?

Answer 1

• Immune response is initiated when the body encounters any foreign molecules acting as exogenous or endogenous antigens).
• Various cytokines released from specific cells, like interleukins (IL), tumor necrosis factor alpha (TNFα), activates the production of mature phagocytic cells, like neutrophils, macrophages and dendritic cells and induce their migration to the site of infection or invasion.
• Phagocytic cells, engulf the foreign substances by phagocytosis or endocytosis.
• The phagocytosed molecules processed and, then the peptide fragments of antigens are expressed through membrane bound glycoproteins called major histocompatibility complex (MHC).
• The antigenic polypeptide bound to MHC molecules further induces B-lymphocytes (designated from Bursa of Fabricus in birds) and T-lymphocytes (lymphocytes maturing in thymus), generating humoral or cell mediated immune responses, as well as immunogenic memory. Such specific activations lead to clonal selection, clonal expansion and clonal deletion.
• Clonal deletion is the process by which immune cells (B-cells or T-cells) that have receotors against self-antigens are eliminated.

Activation of B-lymphocytes-

• B- cells may be activated, by direct interactions with TH cells, and are called response to thymus-dependent (TD) antigens, or may be activated without direct contacts with TH cells, by thymus-independent antigens.
• Cytokines like IL3, IL-4. IL-5 activates TH2 cells.
• TH2 subtype in turn help in activation of B-cells
• These two types of signals may activate naïve B-cells differentiates into memory B-cells and effector B cells (or plasma cells).
• Plasma cells release antibodies. Antibodies, released to the plasma, tissue fluid and lymph, contribute to humoral immunity.