Innate is immediate and non-specific; adaptive is slower, specific and has memory
Mnemonic
“Innate is fast and fixed; adaptive is slow and specific”:
| Innate | Adaptive | |
|---|---|---|
| Speed | Immediate, minutes to hours | Days, 4 to 7 for a primary response |
| Specificity | Broad, pattern recognition | Highly specific |
| Memory | None | Yes, the basis of vaccination |
| Cells | Neutrophils, macrophages, NK cells, dendritic cells, mast cells | T and B lymphocytes |
| Molecules | Complement, lysozyme, interferons, acute phase proteins | Antibodies, cytokines |
Dendritic cells are the bridge, presenting antigen on MHC to prime the adaptive response, which is why they are described as professional antigen presenting cells.
Physical barriers count as innate: skin, mucus, cilia, gastric acid, commensal flora, and their breach is why lines, catheters and burns cause infection.
“Innate deficiency gives recurrent bacterial infection and abscesses; adaptive deficiency depends on which arm.” Antibody failure gives encapsulated bacteria, T cell failure gives viruses, fungi and opportunists.
Expansion
| Feature | Innate | Adaptive |
|---|---|---|
| Speed | Immediate (minutes to hours) | Slow (days) |
| Specificity | Broad pattern recognition | Highly specific |
| Memory | None | Yes |
| Cells | Neutrophils, macrophages, natural killer cells, dendritic cells | T and B lymphocytes |
| Molecules | Complement, lysozyme, interferons, acute phase proteins | Antibodies, cytokines |
| Barriers | Skin, mucus, acid, commensals |
The two are linked by antigen presenting cells, principally dendritic cells, which take up antigen at the periphery and present it on MHC molecules to T cells in lymph nodes, and by cytokines.
Humoral adaptive immunity (B cells and antibody) handles extracellular organisms and toxins; cell-mediated immunity (T cells) handles intracellular pathogens, viruses and tumours.
The memory response is faster, larger and of higher affinity, with a class switch from IgM to IgG. This is the entire basis of vaccination, and the reason a booster produces a much greater response than the priming dose.