What does cell-mediated immunity primarily defend against?

Cell-mediated immunity primarily defends against viruses, certain intracellular parasites, and fungi due to its specific mechanisms involving T lymphocytes, particularly CD8+ cytotoxic T cells. These immune cells are essential in identifying and destroying infected or abnormal cells that harbor pathogens within them. For example, when a cell is infected by a virus, it presents viral antigens on its surface; cytotoxic T cells can recognize these altered cells and initiate targeted immune responses to eliminate the infection.

This type of immunity is crucial because many pathogens can hide inside host cells, where antibodies produced in humoral immunity may not be effective. Additionally, the ability of cell-mediated immunity to also target fungal infections helps explain its broad role in defending against various threats to health.

In contrast, bacteria and extracellular parasites are primarily dealt with by humoral immunity, which involves antibodies and B cells. Allergens and toxins are typically managed by immune responses that do not primarily rely on T cells, while non-infectious agents like chemicals are not pathogens and are usually dealt with through different physiological and detoxification processes.