Question

a cell T as part of the positive selection must be able to:
a) weakly join the MHC itself
b) Avidly recognize your own antigen
c) be able to join MHC and own antigen and activate
d) be able to modify their constant receptor genes

may be more than one option

Answer 1

The T cells are a type of lymphocytes that are produced in the bone marrow but undergo maturation in thymus. The T cells have a central role in the immune response. Since, the T cells have specific receptors on the cell surfaces, they are differentiated from other immune cells. The T cells undergo both positive and negative selection in thymus and thereby differentiate into different types of T cells produced as antigen specific cells and moreover the selection enable the T cells to express distinct cell surface receptors.

The double positive thymocytes such as CD⁴⁺ or CD⁸⁺ cells migrate into deep thymus cortex tissue and express the self antigens. The self antigens are expressed by thymic cortical epithelial cells and on MHC molecules. Only the thymocytes expressing self antigens and can recognze MHCI or MHC II survive and other cells undergo death by neglect. Therefore, the thymocytes are positively selected by interaction cells expressing self antigens having affinity for MHC molecules. The cells that opt to express CD⁴⁺ surface receptors downregulate the genes expressing CD⁸ surface receptors. Therefore, the option c is correct.