Major histocompatibility antigen are products of a cluster of linked genes known as the major histocompatibility complex (MHC).Genes of the I region of the murine MHC exert dramatic control over immune responses.Immune response (Ir)gene products (Ia antigens)may be displayed on lymphocytes as well restrict T and B cell activities.The D region of human MHC appears to be analogous to the mouse I region. B cell or B Lymphocytes, B cell have an mIg (membrane Immunoglobulins)receptor.These cells are derived from pluripotent stem cell in the bone marrow.Progenitor B lymphocytes (pre-B cells)may migrate to several bursa equivalent site to mture,but it is most likely that they mature in the bone marrow itself and the emigrate to the secondary lymphoid organs. Most circulating B lymphocytes express both IgM and IgD,while very few express IgG, IgA,Or IgE.The mIg serve as specific receptors for antigen and,are analogous to TCRs on T cells.Most B cells express class II MHC gene products. Plasma Cells Plasma cells are fully differentiated antibody-synthesizing cells.They are derived from the transitional B lymphocytes following activation of small lymphocytes and populate the lymphoid organs in the immunized host.A plasma cell can be distinguished by its eccentric nucleus,numerous ovoid mitochondria,abundant rough endoplasmic reticulum and prominent Golgi apparatus.It is well adapted for efficient production and packaging of antibodies.The antib body secreted by a single plasma cell (or specific clone)may be of any class (IGM,IgG,IgA,IgD,or IgE).Plasma cells are relatively short-lived (days),compared with circulating B lymphocytes,which may live for years. Non-T and Non-B Lymphocytes A small population of lymphocytes,called null cells,do not express characteristics of either T T cells or B cells.They do not posses hormal levels of the same CD.TCR or mIg surface markers.The majority of these cells are large granular lymphocytes that are derived form pluripotent stem cells in the bone marrow.They migrate to the spleen and lymph nodes but there is about 5%in the blood. Null cells appear quite heterogeneous with respect to surface markers expressed.Most null cells posses receptor f o antibodies that compl with surface antigens on target cell, s the cell through a mechanism know as antibody dependent cellular cytotoxicity (ADCC).In this capacity null cells can be referred to as of killer (K),natural killer (NK),and natural cytotoxic (NC)cells.They are spontaneously cytotoxic to a variety of targets, including a certain cancer cells. Major histocompatibility antigen are products of a cluster of linked genes known as the major histocompatibility complex (MHC). Genes of the I region of the murine MHC exert dramatic control over immune responses. Immune response (Ir) gene products (Ia antigens) may be displayed on lymphocytes as well as macrophages and influence or restrict T and B cell activities. The D region of human MHC appears to be analogous to the mouse I region. B cell or B Lymphocytes , B cell have an mIg (membrane Immunoglobulins) receptor. These cells are derived from pluripotent stem cell in the bone marrow. Progenitor B lymphocytes (pre-B cells) may migrate to several bursa equivalent site to mature, but it is most likely that they mature in the bone marrow itself and the emigrate to the secondary lymphoid organs. Most circulating B lymphocytes express both IgM and IgD, while very few express IgG, IgA, Or IgE. The mIg serve as specific receptors for antigen and, are analogous to TCRs on T cells. Most B cells express class II MHC gene products. Plasma Cells Plasma cells are fully differentiated antibody-synthesizing cells. They are derived from the transitional B lymphocytes following activation of small lymphocytes and populate the lymphoid organs in the immunized host. A plasma cell can be distinguished by its eccentric nucleus, numerous ovoid mitochondria, abundant rough endoplasmic reticulum and prominent Golgi apparatus. It is well adapted for efficient production and packaging of antibodies. The antibody secreted by a single plasma cell (or specific clone) may be of any class (IGM, IgG, IgA, IgD, or IgE). Plasma cells are relatively short-lived (days), compared with circulating B lymphocytes, which may live for years. Non-T and Non-B Lymphocytes A small population of lymphocytes, called null cells, do not express characteristics of either T cells or B cells. They do not possess normal levels of the same CD, TCR or mIg surface markers. The majority of these cells are large granular lymphocytes that are derived form pluripotent stem cells in the bone marrow. They migrate to the spleen and lymph nodes but there is about 5% in the blood. Null cells appear quite heterogeneous with respect to surface markers expressed. Most null cells posses receptor for IgG. By binding to antibodies that complex with surface antigens on target cell, they are able to dill or cytolyses the cell through a mechanism know as antibody dependent cellular cytotoxicity (ADCC). In this capacity null cells can be referred to as of killer (K), natural killer (NK), and natural cytotoxic (NC) cells. They are spontaneously cytotoxic to a variety of targets, including a certain cancer cells