MICROANATOMY

Detailed explanation-1: -All these lymphoid organs contain cells specialized for capturing antigen and presenting it to T cells. The most important of these are the dendritic cells, which capture antigen at the site of infection and then migrate to the downstream lymph node.

Detailed explanation-2: -They are activated on the surface of antigen-presenting cells, which mature during the innate immune responses triggered by an infection. The innate responses also dictate what kind of effector cell a helper T cell will develop into and thereby determine the nature of the adaptive immune response elicited.