A clear differentiation of Th1 and Th2 cytokine-secreting subsets in h
umans has not yet been defined, To further examine cytokine-directed d
ifferentiation of human T cell responses to both exogenous and autoant
igens, we generated 346 short term T cell lines at limiting dilutions
from six normal individuals to tetanus toroid and myelin basic protein
in the presence of IL-2 with or without the addition of IL-12 and ant
i-IL-4 mAb. T cell lines were examined for [H-3]thymidine incorporatio
n and cytokine secretion of IFN-gamma, IL-4, and IL-10. After culture
in the presence of IL-12 and anti-IL-4 mAb, the predominant T cell res
ponse to Ag stimulation was simultaneous secretion of IL-10 and IFN-ga
mma. The concomitant secretion of IL-10 and IFN-gamma by T cells was c
onfirmed by stimulating lines in the absence of APCs with plate-bound
anti-CD3 mAb after two rounds of Ag-specific stimulation. Moreover, IL
-12 enhanced IL-10 and IFN-gamma production in a myelin basic protein-
reactive T cell clone, demonstrating that a differentiated T cell clon
e could be induced to secrete both cytokines, The addition of a neutra
lizing anti-IFN-gamma Ab to cultures with IL-12 and anti-IL-4 mAb duri
ng the generation of tetanus toxoid-reactive lines had no effect on th
e induction of IL-10 and IFN-gamma secretion, indicating that IL-12 an
d not IFN-gamma was responsible for the induction of this subset of T
cells, Thus, in human T cells, IL-12 induces concomitant secretion of
IL-10 and IFN-gamma.