Regulation of the Anti-Inflammatory Cytokines Interleukin-4 and Interleukin-10 during Pregnancy

Pregnant females are susceptible to intracellular pathogens and are biased towards humoral rather than cell-mediated immunity. Since TH1 cytokines compromise pregnancy and TH2 cytokines are produced at the maternal-fetal interface, we hypothesize that these TH2 cytokines inhibit TH1 responses, improving fetal survival but impairing responses against some pathogens.

A cytokine synthesis inhibitory factor (CSIF) is secreted by Th2 clones in response to Con A or antigen stimulation, but is absent in supernatants from Con A-induced Th1 clones. CSIF can inhibit the production of IL-2, IL-3, lymphotoxin (LT)/TNF, IFN-gamma, and granulocyte-macrophage CSF (GM-CSF) by Th1 cells responding to antigen and APC, but Th2 cytokine synthesis is not significantly affected. Transforming growth factor beta (TGF-beta) also inhibits IFN-gamma production, although less effectively than CSIF, whereas IL-2 and IL-4 partially antagonize the activity of CSIF. CSIF inhibition of cytokine synthesis is not complete, since early cytokine synthesis (before 8 h) is not significantly affected, whereas later synthesis is strongly inhibited. In the presence of CSIF, IFN-gamma mRNA levels are reduced slightly at 8, and strongly at 12 h after stimulation. Inhibition of cytokine expression by CSIF is not due to a general reduction in Th1 cell viability, since actin mRNA levels were not reduced, and proliferation of antigen-stimulated cells in response to IL-2, was unaffected. Biochemical characterization, mAbs, and recombinant or purified cytokines showed that CSIF is distinct from IL-1, IL-2, IL-3, IL-4, IL-5, IL-6, IL-7, IFN-gamma, GM-CSF, TGF-beta, TNF, LT, and P40. The potential role of CSIF in crossregulation of Th1 and Th2 responses is discussed.

Interleukin-4 (IL-4) is a pleiotropic lymphokine which plays an important role in the immune system. IL-4 activates two distinct signalling pathways through tyrosine phosphorylation of Stat6, a signal transducer and activator of transcription, and of a 170K protein called 4PS. To investigate the functional role of Stat6 in IL-4 signalling, we generated mice deficient in Stat6 by gene targeting. We report here that in the mutant mice, expression of CD23 and major histocompatibility complex (MHC) class II in resting B cells was not enhanced in response to IL-4. IL-4 induced B-cell proliferation costimulated by anti-IgM antibody was abolished. The T-cell proliferative response was also notably reduced. Furthermore, production of Th2 cytokines from T cells as well as IgE and IgG1 responses after nematode infection were profoundly reduced. These findings agreed with those obtained in IL-4 deficient mice or using antibodies to IL-4 and the IL-4 receptor. We conclude that Stat6 plays a central role in exerting IL-4 mediated biological responses.