Core Framework & Diagram Major Controversies in Immunology History

Metchnikoff insisted immunity was about cells physically engulfing invaders; Ehrlich insisted it was about protective substances in blood. Both were right — antibodies handle bacteria outside cells, T cells handle threats hiding inside them.

The textbook model said immunity attacks anything ‘foreign’. One researcher proposed it actually responds to danger signals, not foreignness. Evidence eventually showed both frameworks are true at once, not competing.

A model split helper T cells into two neat camps. It couldn’t explain Crohn’s disease or several other conditions — until a third type (Th17) was found in 2005, then several more. The original model was a useful simplification, not the complete picture.

A discovery showed NK cells — supposedly memory-free ‘innate’ cells — could remember a past infection after all. The mechanism turned out to be completely different from how T and B cells remember, but the memory itself was real.