Physiology · Blood, hemostasis and basic immunity
Innate and adaptive immunity: overview !
- Concept
- Exam priority: medium
The body has a fast, general defence (innate) and a slower, precise one with memory (adaptive). They work as a team.
Updated 2026-11-01
Also called: Immune system basics
See it in 3D: Thymus · Spleen · Hip bone · Palatine tonsils
What it is
Innate immunity (barriers, phagocytes, complement, NK cells) acts within minutes and recognizes patterns shared by many microbes. Adaptive immunity (B and T lymphocytes) takes days on first contact, recognizes specific antigens and leaves memory, so a second exposure is faster and stronger. This page is a physiology overview; DurgiPedia's Immunology section covers the details.
Key facts
- Passive immunity: maternal IgG crosses the placenta and IgA arrives in breast milk, protecting infants for months.
- HIV infects CD4⁺ T cells, the coordinators of both antibody and cellular responses, which explains opportunistic infections.
The two arms
| Feature | Innate | Adaptive |
|---|---|---|
| Speed | Minutes to hours | Days (first time); faster with memory |
| Recognition | Shared microbial patterns | Specific antigens |
| Memory | No | Yes |
| Main components | Skin and mucosa, neutrophils, macrophages, NK cells, complement | B cells and antibodies, CD4⁺ and CD8⁺ T cells |
Test yourself
Think of the answer, then tap the question to see it.
Why is the second exposure to an antigen met with a faster, stronger antibody response?
The first response leaves memory B and T cells, and B cells have switched class and matured in affinity; on re-exposure they activate quickly and make mainly high-affinity IgG.
Which T cells recognize a virus-infected liver cell and through which molecule?
CD8⁺ cytotoxic T cells, which recognize viral peptides on MHC class I, present on all nucleated cells.
How do innate cells 'know' that a microbe is foreign without prior exposure?
Pattern receptors such as Toll-like receptors, encoded in the germline, bind molecules shared by microbes but absent from human cells, like lipopolysaccharide or bacterial flagellin.
See it in 3D
The structures of Durgical's 3D anatomy where it happens.
Related topics
- White blood cells: types and functions
- The physiology of inflammation
- Blood groups, transfusion and transfusion reactions
- Rh incompatibility
Related conditions
In Biochemistry
Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.
Sources: 21.2 Barrier Defenses and the Innate Immune Response (OpenStax (Rice University), 2022); 21.3 The Adaptive Immune Response: T lymphocytes and Their Functional Types (OpenStax (Rice University), 2022); 21.4 The Adaptive Immune Response: B-lymphocytes and Antibodies (OpenStax (Rice University), 2022); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 35). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016).
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Representative model, for educational purposes only.