Innate vs Adaptive Immunity: Two Systems, One Defence
The immune system is often described as two arms, but in practice it behaves as one continuous defence. Innate immunity acts within minutes: physical barriers, complement proteins, macrophages, neutrophils and natural killer cells detect broad molecular patterns shared by many pathogens.
Adaptive immunity takes days to mount, yet it is precise. B cells and T cells recognise specific antigens through highly variable receptors, expand clonally, and leave behind a memory population that responds far faster on re-exposure.
The handoff between them is where most of the interesting biology happens. Dendritic cells sample tissue, migrate to lymph nodes, and present processed antigen to naive T cells — turning a generic alarm into a targeted, long-lived response.