Recent work on T-helper (Th) cell subset maturation has focused on def
ining the cellular source of early IL-4, which promotes precursor (nai
ve) CD4(+) Th cells to differentiate into Th type 2 (Th2) cells, and a
lso on the roles of counter-regulatory cytokines, costimulatory signal
s, and antigen in the induction of Th2 responses. Results suggest that
not all Th2 cells are equivalent in their ontogeny.