Question

describe how B-cells and T-cells get activated in the adaptive immune response.

Answer 1

The immune system is of two types Acquired and Innate. The adaptive immune system, also known as the acquired immune system, is a subsystem of the immune system eliminates pathogens by preventing their growth.

The white blood cells or lymphocytes carry out the acquired immune response. Two main activities of acquired immune response are antibody responses and cell mediated immune respons which are also carried out by two different lymphocytes , the B cells and T cells. B cells and T cells are derived from the blood producing stem cells called multipotent hematopoietic stem cells, in the bone marrow. Their morphology is indistinguishable from one another until they are activated. B cells leads to humoral immune response(related to antibodies ), and T cells causes cell-mediated immune responses.

Activation of B- cells : In antibody responses, B cells are activated to secrete proteins called antibodies or immunoglobulins. Antibodies travel through the bloodstream and bind to the foreign antigen causing it to activate. This does not allow the antigen to bind to the host cells thus preventing further infection. The B cell receptor present in any one clone of B cells recognizes and binds to only one particular antigen. B cells recognize antigens in their native form. Once a B cell finds its specific antigen it differentiates into an effector cell, known as a plasma cell. Plasma cells are short-lived cells, only for 2-3 days and secrete antibodies. These antibodies bind to antigens, making them easier targets for phagocytes (germ killing cells). CD4+ helper cells produced during t cell activation help in the maturation of B cells into plasma cells and memory B cells.

Activation of T-cells : Naïve T cells are activated when their T-cell receptor (TCR) strongly interacts with a peptide-bound MHC class I molecule of the antigen. The presence of certain cells called antigen-presenting cells or APCs mediate the cellular immune response by processing and presenting the antigens to be recognized by T cells. Examples of APCs are dendritic cells, macrophages, Langerhans cells and B cells ( although their primary role being in humoral immunity) . Once activated, the cytotoxic t cell (CTL) undergoes a process called clonal selection, in which it gains functions and divides rapidly to produce an army of effector cells. Activated CTL then travels throughout the body in search for cells that bear that unique MHC Class I + peptide.The Effector CTL release perforin and granulysin When exposed to these infected cells.These proteins produces cytotoxins that form pores in the target cell's plasma membrane, allowing ions and water to flow into the infected cell, and causing it to burst. In order to limit extensive tissue damage the CTL activation is tightly controlled and helped by additional activation signals . CD4+ cells formed during t cell activation are helper cells and CD8+ cytotoxic cells cause lysis of virus-infected and tumour cells.

Thankyou

Himashree Sarma