T cellB cell collaboration in the immune response to infection Essay

T cellB cell collaboration in the immune response to infection - Essay Example It is referred to as "non-specific" because it generally attempts to stop the spread of all types of invaders. (Kuby, 1996) The latter type consists of two categories: cell-mediated immunity and antibody-mediated (humoral) immunity. It is the stronger one of the two types but takes several hours or even days to become fully activated. It is referred to as "specific" because it responds differently to every other foreign pathogen. (Hariharan, 2006) Lymphocytes, a class of White Blood Cells, are a vital part of the acquired immune system, being responsible for the whole reaction. They are produced in the primary lymphoid organs and then migrate to the secondary lymphoid organs where they recognize antigens of foreign bodies by the help of membrane receptors specific to the antigens. Two major classes of lymphocytes take part in the acquired immunity: B-Cells (B lymphocytes) and T-Cells (T lymphocytes). (Alberts, Bray, Lewis, Raff, Roberts, Watson, 1994), (Linnemeyer, 1993) Precursors of T-cells originate in the foetal liver and yolk sac during the embryonic life, and migrate to the bone marrow after birth. The stem cells then enter the thymus by chemo taxis and develop into T-cells which are later specialized into CD4+ (helper) cells or CD8+ (cytotoxic) cells. (UNC-SOM, 2004) Maturation On entering the thymus, T-cell precursors (prothymocytes) develop into T-cells that indicate both CD4 and CD8 molecules on their membranes and then later continue to indicate either CD4 or CD8 molecules. The cells having antigen receptors for self proteins are destroyed by aptosis (programmed cell death). This prevents autoimmunity. On the other hand, the cells having antigen receptors that do not react with self MHC proteins are also killed as this causes the definite selection of T-cells that do react with MHC proteins. (Stadnyk, 2007) Functions of the MHC proteins include positive selection of T-cells as well as presentation of foreign body antigens to them. (NIAID, 2003) General Function The Helper T-cells activate lymphocytes called macrophages and other T-cells involved in the immune response, and aid B-cells in producing antibodies by alerting them and determining the type of antibody to be produced. (NIAID, 2003) 2) B-Cells: Origin Precursors of B-cells migrate from the foetal liver to the bone marrow where they remain and undergo maturation throughout the adult life. They do not require thymus for their development. (Levinson, 2004) Maturation Development of B-cells takes place in two phases: antigen-independent phase & antigen-dependent phase. In the 1st phase, stem cells of the marrow differentiate into B-lineage and progenitor B-cells. The progenitor B-cells proliferate into precursor B-cells which requires the microenvironment supplied by the surrounding stroma. Cells of the stroma release numerous cytokines, most importantly IL-7, which help in the maturation process. Further