Which type of T cell is responsible for directly attacking and killing other cells?

The type of T cell that directly attacks and kills other cells is the Cytotoxic T-cell. These cells play a critical role in the immune response by identifying and destroying infected cells, cancer cells, and sometimes foreign cells from transplants. They recognize infected or abnormal cells through their T cell receptors, which bind to specific antigens presented on the surface of those cells, usually in the context of major histocompatibility complex (MHC) molecules.

Once Cytotoxic T-cells recognize their targets, they can induce apoptosis (programmed cell death) in those cells, ensuring that the infection or abnormality does not spread. This ability to directly eliminate compromised cells is vital in controlling infections and preventing malignancies.

In contrast, Helper T-cells assist by activating other immune cells, such as B cells and macrophages, but do not kill cells themselves. Regulatory T-cells help maintain immune tolerance and prevent autoimmune responses. Memory T-cells provide long-term immunity by "remembering" past infections, enabling a faster and more efficient response upon re-exposure to the same pathogens.