Cell-mediated immunity (CMI) is a specific type of acquired immune response not mediated by antibodies but by sensitized T cells. This form of immunity is transferred from donor to recipient, not with antisera but with intact lymphocytes; hence it is called cell-mediated immune reaction. CMI performs the following immunological functions:
a) It confers immunity in diseases caused by obligate intracellular bacteria (Mycobacterium tuberculosis, Mycobacterium leprae, Brucella, etc.), viruses (small pox, measles, mumps, etc.), fungi(Histoplasma capsulatum, Blastomyces dermatitidis, Coccidioidesimmitis, etc.), and parasites (Toxoplasma gondii, Leishmania donovani, etc.).
b) It participates in immunological surveillance and immu-nity against cancer.
c) It plays an important role in pathogenesis of delayed hypersensitivity reactions and in pathogenesis of certain autoimmune diseases, such as autoimmune thyroiditis, encephalitis, etc.