Which type of T cell is involved in directly killing infected or cancerous cells?

The type of T cell involved in directly killing infected or cancerous cells is the cytotoxic T cell. These cells, also known as CD8+ T cells, play a crucial role in the immune response by recognizing and binding to specific antigens presented on the surface of infected or malignant cells. Once activated, cytotoxic T cells release perforin and granzymes, which create pores in the target cell's membrane and induce apoptosis, effectively destroying the infected or cancerous cell.

Helper T cells primarily assist in activating other immune cells, such as B cells and cytotoxic T cells, rather than directly killing cells. Regulatory T cells focus on maintaining immune tolerance and preventing autoimmunity rather than participating in direct cell destruction. Memory T cells provide long-term immunity by "remembering" past infections, allowing for a quicker response upon re-exposure to the same pathogen, but they do not directly kill cells themselves. This distinction underscores the specific function of cytotoxic T cells in immune defense against intracellular pathogens and tumors.