Medical Laboratory Scientist ASCP Practice Exam 2025 – Complete Study Guide

Cytotoxic T cells are distinguished by the presence of the CD8 surface marker, which plays a crucial role in their function. These cells are an essential component of the adaptive immune response, specifically targeting and killing infected cells, cancer cells, and sometimes foreign cells from transplants. The CD8 marker serves not only as a co-receptor that enhances the T cell’s response during interactions with antigen-presenting cells but also helps in distinguishing cytotoxic T cells from other T cell types.

In the context of immune function, cytotoxic T cells are activated upon recognition of specific antigens presented by major histocompatibility complex (MHC) class I molecules on the surface of infected or abnormal cells. Once activated, they release cytotoxic granules containing perforin and granzymes, leading to the destruction of the target cell. This process is vital for maintaining the body's defense against intracellular pathogens and cancers.

The other types of T cells listed do not possess the cytotoxic capabilities associated with CD8 expression. Regulatory T cells are primarily involved in maintaining immune tolerance and preventing autoimmunity. Helper T cells (CD4+) assist in the activation of other immune cells such as B cells and cytotoxic T cells but do not directly kill infected cells. Del