Which type of cells recognize fragments of foreign antigens presented with self antigens?

• A. B cells
• B. Macrophages
• C. T cells
• D. Natural killer cells

Answer: (C)

The recognition of fragments of foreign antigens presented with self antigens is a key function of T cells, specifically the helper T cells (CD4+) and cytotoxic T cells (CD8+). These cells are equipped with T cell receptors (TCRs) that specifically bind to peptide fragments of antigens that are displayed on the surface of antigen-presenting cells in association with major histocompatibility complex (MHC) molecules.

When a pathogen invades the body, immune cells such as macrophages and dendritic cells ingest and process these pathogens, presenting the resulting antigen fragments on their surface alongside self antigens through MHC molecules. This process is crucial for the immune response, as it allows T cells to recognize and respond to infected or abnormal cells. Helper T cells initiate and coordinate the immune response, while cytotoxic T cells directly kill infected or cancerous cells.

The ability of T cells to recognize these antigen fragments is critical for the adaptive immune response, allowing for specific targeting of invasive pathogens while distinguishing them from the body's own cells.