Which statement about T-cell maturation is true regarding positive selection?

The correct answer highlights the crucial role of positive selection in T-cell maturation, specifically emphasizing the interaction between T-cell receptors (TCRs) and major histocompatibility complex (MHC) molecules. During positive selection, developing T cells, or thymocytes, that are capable of recognizing self-MHC molecules are allowed to mature. This process ensures that T cells can effectively interact with antigen-presenting cells in the immune response while retaining some degree of self-tolerance.

Mature T cells that weakly bind to MHC molecules presenting self-antigens are positively selected because they have the potential to function within the immune system without being overly reactive to self-tissues. This process is vital in establishing a functional T-cell repertoire that can respond to foreign antigens without causing autoimmunity.

In contrast, options that suggest low affinity for antigens leads to maturation, involve the death of all T cells, or confuse positive selection with negative selection do not align with the established understanding of T-cell development and selection processes. Positive selection is designed to retain T cells that can recognize self-MHC while negatively selecting those that react too strongly to self-antigens, ensuring a functional immune response. Thus, the second option best describes the true nature of positive selection in T