Adaptive Immunity
One-Sentence Definition
Adaptive immunity is antigen-specific, memory-capable host defense mediated by B and T lymphocytes — the basis of Vaccination, serologic diagnosis, and long-term protection after infection.
Simple Explanation
After first exposure, the immune system learns and remembers — faster and stronger on the next encounter.
Detailed Scientific Explanation
| Arm | Cell | Product / function | Micro example |
|---|---|---|---|
| Humoral | B cells → plasma cells | Antibodies and Immunoglobulin Classes | Anti-tetanus IgG; anti-HBs |
| Cellular | CD4+ T helper | Cytokine help, macrophage activation | TB granuloma control |
| CD8+ cytotoxic T | Kill infected cells | Viral clearance (HBV, CMV) | |
| Memory | Memory B/T | Rapid recall response | Vaccine protection |
Key concepts
- Primary vs secondary response — faster, higher-affinity antibodies after re-exposure
- Affinity maturation — germinal centre selection
- Immunological memory — basis of boosters and some serology interpretation
- Tolerance — failure to respond to Normal Microbiota appropriately
Pathogen evasion of adaptive immunity:
- Antigenic Variation (influenza, gonococcus)
- Superantigens (Streptococcus pyogenes)
- Intracellular niches (TB, chlamydia, viruses)
- Latency (HSV, CMV, EBV)
Mechanism
Antigen presentation (MHC I/II) → clonal selection → effector + memory lymphocytes.
Clinical Importance
- Immunosuppression → reactivation (CMV, TB, HSV)
- Vaccine schedules exploit memory formation
- Seroconversion windows affect diagnostic timing
Research Importance
- AI for Vaccine Design — epitope selection
- T-cell epitope mapping for TB/HIV vaccines
Diagnostic Relevance
- Paired serology (IgM/IgG rise) for some infections
- T-cell assays (IGRA for TB)
AMR Relevance
- Indirect — better prevention reduces antibiotic use
Related MOCs
Active Recall Questions
- Humoral vs cellular — which clears extracellular encapsulated bacteria?
- Why do some polysaccharide vaccines fail in infants without conjugation?
- Name one pathogen that uses antigenic variation.