Sentinels of the Type 2 Immune Response.

Type 2 immune responses have evolved to sense and respond to large, non-replicating infections or non-microbial noxious compounds in tissues. The development of these responses therefore depends upon highly coordinated and tightly regulated tissue-residing cellular sensors and responders. Multiple exposure to type 2 helper T cell (Th2)-inducing stimuli further enhances both the diversity and potency of the response. This review discusses advances in our understanding of the interacting cellular subsets that comprise both primary and secondary type 2 responses. Current knowledge regarding type 2 immune responses in the lung are initially presented and are then contrasted with what is known about the small intestine. The studies described portray an immune response that depends upon well-organized tissue structures, and suggest their modulation as a therapeutic strategy.