Question

With regard to T cell development in the thymus. How are tissue specific antigens expressed in the thymus?

Answer 1

Two type of lymphocytes present, both originate from bone marrow but maturation takes place in different places like those who matures in thymus known as T-cells and those who matures in bone marrow known as B-cells. Although other than this, some other forms also present in the immune system with respect to lymphocytes. Thymus is most important organ for immune system and it is a lymphoid organ and eventually this organ reduces with age of an individual that's why you see compromised immune system in elderly aged people.

In thymus gland some particular cells are specific for antigen expression and present on the periphery of the cells known as PAE cells of thymus and they are auto-immune regulator elements (proteins) aka AIRE and they would be part of negative selection, in this condition T cell act against some molecules particularly protein as they behave like antigen to the system and these T cell eliminate such elements from the system through apoptosis like thymocytes. Other cells of the thymus express response to other parts of the body (other than thymus itself) for example dendritic cells and epithelial cells.