Schistosoma mansoni egg-primed Th0 and Th2 cells: failure to down-regulate IFN-gamma production following in vitro culture.

Schistosoma mansoni eggs induce a rapid and pronounced Th response which, based on cytokine secretion patterns, at day 3 post priming is Th0-like and at day 10 is Th2-like. To establish whether or not the day-3 cells have been programmed in vivo to develop into Th2 cells, they were cultured for 7 days to become in vitro equivalents of day-10 in vivo cells. Following this culture period, the population was approximately 75% CD4+, 22% CD8%, 6% B220+ and capable of producing IL-2, IFN-gamma, IL-4, -5 and -10 upon stimulation. This Th0-like status was confirmed by the observations that in response to mitogen IL-4 and IFN-gamma production are both CD(4+)-cell dependent and that IFN-gamma and IL-4 are produced concomitantly by single cells. These data suggest that Th0 cells persist in vivo, but are incapable of secreting IFN-gamma at day 10 due to an inhibitory factor which does not develop or is labile in vitro. This concept is supported by the surprising observation that day-10 LN cells, which are Th2-like immediately ex-vivo, rapidly gain the ability to secrete IFN-gamma following a short period of culture.