Pathogens, Commensals and First-Line Defence
Trillions of microorganisms live on your skin, in your mouth and in your gut, and almost none of them cause harm. Episode 1 of the immunology series asks what makes the rare one dangerous: the four kinds of pathogen, why damage rather than species or number defines the line between commensal and pathogen, the three host strategies, and the four layers of defence and how fast each one acts.