When does positive and negative selection of T cells occur?

Positive and negative selection of T cells is a crucial process that occurs after the rearrangement of T cell receptor (TCR) genes. This selection process takes place in the thymus, where immature T cells undergo a series of developmental stages to ensure that they can effectively recognize and respond to foreign antigens while avoiding autoimmunity.

During positive selection, T cells that successfully recognize self-MHC molecules receive survival signals, allowing them to mature and continue the selection process. On the other hand, negative selection ensures that T cells with high affinity for self-antigens are eliminated, thus preventing potential autoimmune responses. This process helps establish a functional and self-tolerant T cell repertoire that can effectively respond to infections and other challenges once they exit the thymus for peripheral circulation.

The processes mentioned are intricately tied to TCR gene rearrangement because TCRs must be generated and expressed for T cells to identify and respond to MHC molecules and their respective antigens. Thus, the timing of these selection processes being after TCR gene rearrangement is critical for the development of a diverse and functional T cell population.