Paper I
Question
List the various roles of Cell mediated immunity with specific examples.
Answer
Roles of Cell-Mediated Immunity (CMI), with specific examples:
- Defence against intracellular pathogens — Th1 cells activate macrophages (via IFN-γ) to kill intracellular bacteria; e.g., Mycobacterium tuberculosis, Leishmania donovani.
- Direct killing of virus-infected cells — CD8+ cytotoxic T lymphocytes recognize viral peptides on MHC class I and kill infected cells via perforin/granzyme; e.g., clearance of influenza virus, HSV-infected cells.
- Tumour immune surveillance — cytotoxic T cells recognize and kill tumour cells expressing tumour-associated/neo-antigens; the basis of cancer immunotherapy (e.g., CAR-T cell therapy).
- Granuloma formation — CMI (via IFN-γ-activated macrophages) contains organisms that cannot be fully eliminated, walling them off in granulomas; e.g., containment of M. tuberculosis in the primary complex.
- Graft rejection — CD8+ CTLs and CD4+ T cells mediate acute cellular rejection of allografts, recognizing foreign MHC.
- Delayed-type hypersensitivity — sensitized Th1 cells drive the tuberculin (Mantoux) skin reaction and contact dermatitis.
- Help for B-cell antibody responses — CD4+ T-follicular helper cells provide help for B-cell class switching and affinity maturation in germinal centres, linking CMI to humoral immunity.