Which immune cells are primarily responsible for the cytotoxic response against infected cells?

The primary immune cells responsible for the cytotoxic response against infected cells are CD8 T cells, also known as cytotoxic T lymphocytes. These cells are crucial in identifying and destroying cells infected with viruses or other intracellular pathogens. CD8 T cells recognize specific antigens presented by major histocompatibility complex (MHC) class I molecules, which are found on nearly all nucleated cells in the body. When a CD8 T cell binds to an infected cell displaying a foreign antigen, it can initiate a series of cytotoxic actions, including the release of perforin and granzymes. Perforin creates pores in the target cell’s membrane, while granzymes enter through these pores to induce apoptosis (programmed cell death) in the infected cell.

In contrast, CD4 T cells primarily function as helpers that support other immune cells, including activating CD8 T cells and aiding in the immune response without directly killing infected cells. Natural killer (NK) cells also participate in the cytotoxic response, particularly against cancerous or virally infected cells, but they operate through a different mechanism and do not require antigen specificity as CD8 T cells do. B cells are primarily responsible for antibody production and do not directly kill infected cells; instead