Immunology and Defense Mechanisms
Core concepts
Distinguish innate (non-specific: skin, mucus, phagocytes, inflammation, complement) from adaptive immunity (specific: B and T lymphocytes, antibodies, memory). Know humoral immunity (B cells → plasma cells → antibodies) and cell-mediated immunity (T cells, cytotoxic T cells killing infected cells, helper T cells coordinating). Understand antigens, antibody structure, primary vs. secondary response, vaccination, and the basis of allergies and autoimmune disease.
Traps in questions
- Antibodies are produced by plasma cells (differentiated B cells), not by T cells.
- The secondary immune response is faster and stronger because of memory cells.
- Helper T cells recognize antigen presented on MHC; cytotoxic T cells kill infected cells.
- Innate immunity has no memory and is not antigen-specific.
- Vaccination provides active immunity; injected antibodies provide passive immunity.
Worked example / rule of thumb
Vaccination: antigen introduced → primary response (antibodies + memory cells) → later exposure → rapid secondary response → protection. Rule of thumb: who makes it, who kills it, who remembers it - B/plasma cells make antibodies, cytotoxic T cells kill infected cells, memory cells remember.