Which type of T cell is primarily involved with exogenous antigens?

• A. CD-4
• B. CD-8
• C. Regulatory T cells
• D. Memory T cells

Answer: (A)

The type of T cell primarily involved with exogenous antigens is the CD-4 T cell. CD-4 T cells, also known as helper T cells, play a crucial role in the immune response by recognizing antigens presented by antigen-presenting cells (APCs) on major histocompatibility complex (MHC) class II molecules. Exogenous antigens are typically derived from outside the body, such as bacteria or foreign proteins, and are internalized by APCs, processed, and then displayed on MHC class II.

When a CD-4 T cell encounters its specific antigen presented on an MHC class II molecule, it becomes activated. This activation leads to the secretion of cytokines that assist in orchestrating a broader immune response, stimulating B cells to produce antibodies and promoting the activation of CD-8 T cells and other immune cells. This function is vital for an effective adaptive immune response against pathogens that enter the body from the external environment.

In contrast, CD-8 T cells primarily recognize endogenous antigens presented on MHC class I molecules, typically associated with intracellular pathogens such as viruses. Regulatory T cells are focused on maintaining immune tolerance and preventing autoimmunity, while memory T cells are responsible for long-term immunity and rapid