Polarization of Th-cell responses: a phylogenetic consequence of nonspecific immune defence?

CD4+ T helper (Th)-cell responses are polarized into Th1 and Th2 types. Here, Paul Garside and Allan McI. Mowat propose that this is an evolutionary consequence of the relationship between specific adaptive immunity, individual components of the nonspecific inflammatory response and different types of infection. This concept has important implications both for understanding protective immunity and for vaccine design and delivery.