What characteristic differentiates T cytotoxic cells from other T cells?

The distinguishing characteristic of T cytotoxic cells is their ability to directly kill infected cells. These cells, also known as CD8+ T cells, play a critical role in the adaptive immune response by identifying and eliminating cells that have been compromised by viral infections or transformed by cancer. Once activated, T cytotoxic cells can recognize specific antigens presented by infected or abnormal cells through major histocompatibility complex (MHC) class I molecules. This recognition leads to the release of cytotoxic substances, such as perforin and granzymes, which induce apoptosis in the target cell.

This direct killing mechanism sets T cytotoxic cells apart from other types of T cells, such as T helper cells, which primarily assist other immune cells rather than engage in direct destruction of pathogens. T helper cells provide critical signals to activate B cells and enhance the function of other immune cells but do not have the capability to kill infected cells themselves. Similarly, T regulatory cells focus on maintaining immune homeostasis rather than targeting pathogens directly. Therefore, the capacity of T cytotoxic cells to kill infected cells is a defining feature that highlights their unique function within the immune system.