Which type of cells destroy the cells where antigens have invaded?

Killer T cells, also known as cytotoxic T lymphocytes, have the primary function of identifying and destroying cells that have become infected with pathogens or have become cancerous. They recognize cells displaying foreign antigens on their surface, which typically occurs when those cells present fragments of the antigens they are harboring. Upon recognition, Killer T cells release perforins and granzymes, which lead to the lysis (destruction) of the infected or dysfunctional cells.

This distinct role separates Killer T cells from the other types listed. For instance, activated helper T cells support immune responses by stimulating B cells and other immune cells, while suppressor T cells help regulate and diminish the immune response to avoid overactivity. Helper T cells do not directly kill infected cells; instead, they enhance the overall response of the immune system. Therefore, the specific function of Killer T cells in directly targeting and eliminating infected or malignant cells makes them the correct answer.