Flow cytometry in a 3-year-old patient shows normal CD4+ T cells and B cells, but low CD8+ T cells. Which type of immunity would be affected?

• A. Elimination of virally infected cells
• B. Production of antibody
• C. Formation of plasma cells
• D. Downregulation of the immune response

Answer: (A)

CD8+ T cells are the main players in cell-mediated immunity, specialized to directly kill virally infected or abnormal cells. They become cytotoxic T lymphocytes that recognize viral peptides presented on MHC class I molecules on infected cells. Upon engagement, they release perforin and granzymes to induce apoptosis of the target cell, stopping viral replication and spread.

If CD8+ T cells are low, this cytotoxic killing pathway is impaired, so the body’s ability to eliminate virally infected cells diminishes. The presence of normal CD4+ T cells and B cells means humoral immunity (antibody production) and plasma cell formation can still function, because CD4+ help supports B cell activation and antibody generation. Downregulation of the immune response involves regulatory mechanisms and is not the primary issue here.