You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is Which of the following features is not shared between T cells and B cells and explain in detail?
Ans. (a) Positive selection during development B cell undergoes negative selection, whereas T cells undergoes both positive and negative selection. Mechanism of central tolerance: B cell: The recognition of antigens by the immature B-cells in the bone marrow is critical to the development of immunological tolerance to self. For proper immunological function it is essential B cell do not recognize self antigen and should recognize antigen derived from pathogens. In the bone marrow the immature B cells bearing surface IgM, if recognizes self molecule undergo negative selection. This self antigen induce loss of cells from the B cell repeoire is called as clonal deletion. Thus only those B cells that do not recognizes self molecules as antigen comes out of bone marrow. T cells tolerance: T cells are selected for survival more rigorously than B cells. They undergo both positive and negative selection to produce T cells that recognizes self MHC but do not recognizes self peptides. T cell tolerance is induced in thymus. (i) Positive selection occurs in thymic coex, if a maturing T cell is able to bind to a surface MHC molecule it is saved from program cells death; whereas cells fails to recognize MHC dies. Positive selection ensures that T cell recognize antigen in association with MHC molecule only. (ii) Negative selection occurs in coex, coico-medullary junction, and the medulla. Here MTEC (modullary thymic epithelial cells) signal self reactive T cells to die apoptosis. Other Options Option b: Class I MHC are expressed by all nucleated cells and platelets. Ref. Robbin's 8/e 190 Option c: Both B cells and T cell possess antigen receptors. On B cells surface Ig acts as antigenic receptor whereas on T cell, TCR along with CD3 acts as antigenic receptors. Ref. AA 8/e 128, 9/e, p 133