Immunology · Adaptive immunity
Adaptive immunity (overview: humoral vs cellular) !
- Topic
The trained part of the immune system: T and B cells that recognize one target precisely and remember it.
Updated 2026-11-01
What it is
Adaptive immunity is carried out by lymphocytes whose receptors are generated by random gene rearrangement, so each clone recognizes one epitope. Humoral immunity uses antibodies made by B cells and plasma cells against extracellular microbes and toxins; cellular immunity uses T cells against intracellular pathogens and to coordinate the whole response. It is slower at first than innate immunity but specific, and it leaves memory.
Key facts
- Specificity comes from V(D)J recombination by the RAG1 and RAG2 enzymes.
- Clonal selection: only lymphocytes that meet their antigen proliferate.
- T cells see processed peptides on MHC; B cells see native antigen in its original shape.
- Tolerance mechanisms remove or silence self-reactive lymphocytes.
Humoral versus cellular immunity
| Feature | Humoral | Cellular |
|---|---|---|
| Main cells | B cells, plasma cells | CD4 helper and CD8 cytotoxic T cells |
| Effector | Antibodies | Cytokines and direct killing |
| What it recognizes | Native antigen (proteins, polysaccharides, lipids) | Peptides presented on MHC |
| Best against | Extracellular bacteria, toxins, free viruses | Viruses, intracellular bacteria, tumor cells |
| Transfer to another person | Serum or antibodies (passive immunity) | Only with cells |
Clinical notes
- B-cell defects (for example X-linked agammaglobulinemia) cause recurrent infections by encapsulated bacteria.
- T-cell defects cause viral, fungal and opportunistic infections; HIV depletes CD4 T cells.
- Combined defects (severe combined immunodeficiency) are life-threatening from early infancy.
Test yourself
Think of the answer, then tap the question to see it.
What are the two defining features of adaptive immunity?
Specificity for a single epitope and immunological memory.
Which arm of adaptive immunity mainly protects against extracellular toxins?
Humoral immunity: neutralizing antibodies made by plasma cells.
Which enzymes generate the diversity of T- and B-cell receptors?
RAG1 and RAG2, which carry out V(D)J recombination.
What pattern of infections suggests a T-cell defect?
Viral, fungal and opportunistic infections (for example Pneumocystis or severe candidiasis), often with failure to thrive.
Related
- Innate immunity (overview, barriers)
- MHC/HLA class I and II
- Antigen processing and presentation
- T-cell activation: two signals and superantigens
- B-cell activation, class switching and affinity maturation
- Antibody structure and isotypes (IgG, IgA, IgM, IgE, IgD)
- Primary vs secondary response and memory
- CD4⁺ helper T cell
- CD8⁺ cytotoxic T cell
- B cell and plasma cell
- Lymph node: cortex, paracortex, medulla
- T-cell and combined deficiencies: DiGeorge, SCID, Wiskott–Aldrich, ataxia-telangiectasia
- B-cell (antibody) deficiencies: XLA, CVID, IgA deficiency, hyper-IgM
Educational content on the immune system; not a treatment or individual vaccination guide and no substitute for a health professional's advice. No doses are given.
Sources: 18.1 Overview of Specific Adaptive Immunity (OpenStax (Microbiology), 2016); 21.3 The Adaptive Immune Response: T lymphocytes and Their Functional Types (OpenStax (Anatomy and Physiology 2e), 2022); 21.4 The Adaptive Immune Response: B-lymphocytes and Antibodies (OpenStax (Anatomy and Physiology 2e), 2022).
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Representative model, for educational purposes only.