IL-4 and IL-10 antagonize IL-12-mediated protection against acute vaccinia virus infection with a limited role of IFN-gamma and nitric oxide synthetase

: Resistance or susceptibility to most infectious diseases is strongly determined by the balance of type 1 vs type 2 cytokines produced during infection. However, for viruses, this scheme may be applicable only to infections with some cytopathic viruses, where IFN-gamma is considered as mandatory for host defense with little if any participation of type 2 responses. We studied the role of signature Th1 (IL-12, IFN-gamma) and Th2 (IL-4, IL-10) cytokines for immune responses against vaccinia virus (VV). IL-12-/-mice were far more susceptible than IFN-gamma-/- mice, and primary CTL responses against VV were absent in IL-12-/- mice but remained intact in IFN-gamma-/- mice. Both CD4+ and CD8+ T cells from IL-12-/- mice were unimpaired in IFN-gamma production, although CD4+ T cells showed elevated Th2 cytokine responses. Virus replication was impaired in IL-4-/- mice and, even more strikingly, in IL-10-/- mice, which both produced elevated levels of the proinflammatory cytokines IL-1alpha and IL-6. Thus, IL-4 produced by Th2 cells and IL-10 produced by Th2 cells and probably also by macrophages counteract efficient anti-viral host defense. Surprisingly, NO production, which is considered as a major type 1 effector pathway inhibited by type 2 cytokines, appears to play a limited role against VV, because NO sythetase 2-deficient mice did not show increased viral replication. Thus, our results identify a new role for IL-12 in 2† Resistance or susceptibility to most infectious diseases is strongly determined by the balance of type 1 vs type 2 cytokines produced during infection. However, for viruses, this scheme may be applicable only to infections with some cytopathic viruses, where IFN- g is considered as mandatory for host defense with little if any participation of type 2 responses. We studied the role of signature Th1 (IL-12, IFN- g ) and Th2 (IL-4, IL-10) cytokines for immune responses against vaccinia virus (VV). IL-12 2 / 2 mice were far more susceptible than IFN- g 2 / 2 mice, and primary CTL responses against VV were absent in IL-12 2 / 2 mice but remained intact in IFN- g 2 / 2 mice. Both CD4 1 and CD8 1 T cells from IL-12 2 / 2 mice were unimpaired in IFN- g production, although CD4 1 T cells showed elevated Th2 cytokine responses. Virus replication was impaired in IL-4 2 / 2 mice and, even more strikingly, in IL-10 2 / 2 mice, which both produced elevated levels of the proinﬂammatory cytokines IL-1 a and IL-6. Thus, IL-4 produced by Th2 cells and IL-10 produced by Th2 cells and probably also by macrophages counteract efﬁcient anti-viral host defense. Sur-prisingly, NO production, which is considered as a major type 1 effector pathway inhibited by type 2 cytokines, appears to play a limited role against VV, because NO sythetase 2-deﬁcient mice did not show increased viral replication. Thus, our results identify a new role for IL-12 in defense beyond the induction of IFN- g and show that IL-4 and IL-10 modulate host protective responses Endogenous IL-4 and IL-10 inhibit clearance of VV infection It has been well established that IL-4 and IL-10 can inhibit type 1 responses and prevent clearance of some pathogens (2). To assess the role of these cytokines during infection with VV, we measured virus titers in ovaries of IL-4 2 / 2 mice, IL-10 2 / 2 mice (both C57BL/6), and wild-type mice infected with varying doses (10 4 , 10 6 , and 10 8 pfu) of VV (WR) or with 10 6 pfu of recombinant VV-G2. A dose of 10 8 pfu was lethal for wild-type mice (3/3) and for IL-4 2 / 2 mice (2/3). In contrast, IL-10 2 / 2 mice showed a dra-matically reduced virus titer ranging between 10 3 - to 10 4 -fold after infection with low, intermediate, and high doses of VV (WR) and VV-G2 at day 6 after infection (Fig. 2). Virus titers were reduced 10- to 20-fold as early as day 3 after infection. In IL-4 2 / 2 mice, virus titers in ovaries were reduced 80-fold after infection with 10 6 pfu VV (WR), whereas virus replication was not signiﬁcantly different after infection with low doses (10 4 pfu) of VV (WR) or with 10 6 pfu of VV-G2 (Fig. 2). These results demonstrate that endogenous IL-4 and, in particular, IL-10 inhibit VV clearance. IL-4 production depends mainly on differentiated type 2 effector T cells producing a panel of type 2 cytokines including IL-10, suggesting that IL-4 may be important later in infection during the acquired response. In contrast, IL-10 can be produced by, and act as an autocrine inhibitor of, macrophages early after infection, which may explain the ﬁnding that IL-10 is more potent than IL-4 in suppression of host defense.