Question

Are bone-marrow derived cells primarily responsible for selecting against newly developed T cells that would attack self-MHC proteins as antigens. Yes, yes of course they are. Is this then an example of negative selection? Explain

Answer 1

T lymphocytes are those which complete their maturaion in the thymus endocrine gland. These cells attain their T cell receptors in the thymus gland. During their maturation, they are selected based on their strength of interaction with the MHC complexes present on every nucleated cells. Dendritic cells and macrophages which originate from bone marrow also have MHC II complex on their surface which display the self antigens on the surface of MHC. If the Immature T cells fail to recognize and interact with selfantigen and self MHC complex, they are rejected and under go non-selection. Those which can recognize and moderately bind to MHC , they survive and leave the thymus to enter in to secondary lymphoid organs. Those which bind to MHC more strongly, they also undergo apoptosis which is a negative selection process. These are negatively selected because these cells are potential auto reactive cells. Which means they may attck the self antigen instead of a foreign antigen. To stop such an auto rective condition, these cells are destroyed and it is called negative selection. Yes, dendritic cells and macrophages are produced by bone marrow which are involved in negative selection in thymus. The purpose of selection is to allow only those cells which can recognize the self antigen and self MHC.