What happens to T cells after positive and negative selection?

After positive and negative selection in the thymus, the fate of T cells is determined based on their interactions with self-antigens presented by major histocompatibility complex (MHC) molecules. 

During positive selection, immature T cells that can effectively recognize MHC molecules with moderate affinity survive and continue their maturation process. 

T cells that have successfully passed positive selection proceed to negative selection. In this stage, thymocytes that display a high affinity for self-antigens presented by MHC molecules are eliminated. The goal of negative selection is to prevent the development of T cells that could cause autoimmune responses if they were to encounter self-antigens in the periphery.

After positive and negative selection, the surviving T cells, also known as the mature T cells, leave the thymus and enter the peripheral lymphoid organs. On encountering their specific antigens, the mature T cells get activated and become effector T cells, performing various immune functions such as directly attacking infected or abnormal cells, helping other immune cells or coordinating immune responses.