Which immune cell is primarily activated by MHC class I molecules?

MHC class I molecules play a crucial role in the immune system by presenting endogenous antigens, typically derived from proteins synthesized within the cell, to the immune cells. The primary cells that recognize these MHC class I molecules are CD8+ T cells, also known as cytotoxic T lymphocytes.

When a cell is infected by a virus or undergoes transformation, it produces abnormal proteins, which are processed and presented on MHC class I molecules on the cell's surface. CD8+ T cells have specific receptors, known as T cell receptors (TCRs), that recognize these MHC class I-antigen complexes. Upon recognition, CD8+ T cells become activated, proliferate, and differentiate into effector cells that can directly kill infected or abnormal cells by inducing apoptosis.

In contrast, B cells primarily respond to antigens presented via MHC class II molecules and are involved in humoral immunity, while CD4+ T cells primarily recognize antigens presented by MHC class II molecules, contributing to the activation of other immune cells. Natural Killer (NK) cells, while they can recognize and kill infected or transformed cells, do not require MHC class I molecules for activation, as they can respond to cells with reduced MHC class