LIFE SCIENCE

Detailed explanation-1: -First, some T cells undergo a process of positive selection which leads specifically-reactive immature thymocytes to survive and differentiate into mature functional T cells. Second, T cells with high affinity for H-2 molecules undergo negative selection (tolerance).

Detailed explanation-2: -Negative Selection of T Cells Negative selection removes thymocytes that are capable of strongly binding with self-antigens presented by MHC. Thymocytes that survive positive selection migrate towards the boundary of the thymic cortex and thymic medulla (the part of the thymus where T cells enter circulation).

Detailed explanation-3: -During this phase, T cells with self-reactive antigen receptors are eliminated by negative selection, and T cells that can recognize foreign peptides bound to polymorphic self-MHC molecules are selected to mature (positive selection.