Question

T cells must be able to distinguish self from non-self. The

process is referred to as the ____________________

Answer 1

The process by which T cells are able to distinguish self from non-self and avoid destroying the body's own tissues is called T cell tolerance, involving a combination of positive and negative selection within the thymus known as central tolerance.

Step-by-step explanation:

T cells must be able to distinguish self from non-self. The process by which this is achieved is referred to as T cell tolerance. While thymocytes, which are immature T cells, are in the cortex of the thymus, they go through positive selection, a key part of T cell development and differentiation. This process involves binding to the major histocompatibility complex (MHC) molecules they observe on thymic epithelia, selecting MHC molecules of "self." A large number of thymocytes fail this selection and are destroyed.

Subsequently, thymocytes that begin to express both CD4 and CD8 molecules, known as double positives, undergo negative selection at the junction between the cortex and the medulla of the thymus. Here, self-antigens presented by professional antigen-presenting cells induce the elimination of self-reactive T cells through apoptosis. The central tolerance involves this negative selection within the thymus, while peripheral tolerance further ensures that self-reactive immune responses are controlled in the body, preventing autoimmunity.

Answer 2

The process by which T cells learn to distinguish self from non-self is known as T cell tolerance, involving both positive and negative selection in the thymus to eliminate self-reactive T cells and prevent autoimmune diseases.

Step-by-step explanation:

T cells must be able to distinguish self from non-self. The process is referred to as T cell tolerance. This is a critical component of the immune system's ability to prevent autoimmune diseases, where the body would otherwise attack its own tissues.

During T cell differentiation in the thymus, developing T cells undergo positive and negative selection processes. This ensures that T cells recognizing self-antigens are eliminated. Positive selection occurs when thymocytes express both CD4 and CD8 receptors and bind to the body's own MHC molecules in the thymus, signifying that they can appropriately recognize self-MHC molecules. Thymocytes that cannot bind to self-MHC are eliminated.

Negative selection is another crucial step in this process. This phase occurs at the boundary of the thymus cortex and medulla, where T cells that react too strongly to self-antigens presented by professional antigen-presenting cells are induced to die by apoptosis. The resulting mature T cells are then capable of recognizing only non-self antigens presented on self-MHC molecules, effectively allowing them to combat pathogens without harming the body's own cells.

Disruptions to T cell tolerance mechanisms can lead to their breakdown and the onset of autoimmune responses, where the immune system erroneously targets self-tissues. This sheds light on the precarious balance the immune system must maintain to distinguish between self and non-self while protecting the body from external threats.