Failure to induce neonatal tolerance in mice that lack both IL-4 and IL-13but not in those that lack IL-4 alone

Current evidence suggests that neonatal tolerance to a foreign Ag is the co nsequence of IL-4-mediated Th2 immunity rather than the thymic deletion of Ag-specific T cells. Here, we addressed the role of IL-4 in neonatal tolera nce by testing whether tolerance to a minor histocompatibility Ag can be in duced in newborn mice that lack IL-4 (IL-4(-/-)). We found that IL-4 does n ot play a dominant role in the induction of neonatal tolerance as newborn f emale IL-4(-/-) mice could be readily tolerized to the H-Y male Ag. In cont rast, mice that lack both IL-4 and IL-13 (IL-4(-/-)/IL-13(-/-)) were resist ant to the induction of neonatal tolerance, and their splenocytes produced exaggerated amounts of IFN-gamma on rechallenge with the same Ag encountere d during the neonatal period. These findings argue against the view that IL -4 alone is critical for the induction of neonatal tolerance and suggest th at the combined actions of both IL-4 and IL-13 are essential for this proce ss.