Study summary · research use only
IL-4 inhibits vasoactive intestinal peptide production by macrophages
Plain-language summary
Paraphrased from the published abstract below — not a verdict on whether anything works.
This mouse study examined regulation of vasoactive intestinal peptide (VIP) production by macrophages in the context of schistosomiasis-induced granulomas. Splenocytes from uninfected C57BL/6 mice expressed VIP mRNA and protein, which the authors reported stopped after schistosome egg deposition. Because eggs induce a Th2 response, the authors tested whether interleukin-4 (IL-4) regulates VIP, finding that recombinant IL-4 inhibited VIP mRNA expression in splenocytes, with F4/80+ macrophages identified as the constitutive VIP source subject to this regulation. In IL-4 knockout mice, splenic VIP production did not decline during infection, and granuloma VIP was found to derive from non-macrophage (F4/80-negative) cells, while macrophages from IL-4 knockout mice still expressed VIP.
Abstract
In schistosomiasis, eggs induce granulomas that have a vasoactive intestinal peptide (VIP) immunoregulatory circuit. This study explored the regulation of VIP production at sites of inflammation. Splenocytes from uninfected C57BL/6 mice expressed VIP mRNA and protein, which stopped following egg deposition. Eggs induce a Th2 response, suggesting that Th2 cytokines like interleukin (IL)-4 can regulate VIP. To address this issue, splenocytes from uninfected mice were incubated for 4 h with or without recombinant IL-4. IL-4 inhibited VIP mRNA expression. F4/80+ macrophages were the source of constitutively expressed VIP, subject to IL-4 regulation. In IL-4 knockout mice, splenic VIP production did not downmodulate during schistosome infection, suggesting that IL-4 is a critical cytokine regulating VIP production in wild-type mouse spleen. IL-4-producing granulomas in schistosomiasis made VIP. Experiments showed that granuloma VIP derived from F4/80- (nonmacrophage) cell populations, explaining this paradox. Granuloma F4/80+ cells from IL-4 knockout mice expressed VIP. Thus macrophages can make VIP, which is subject to IL-4 regulation. However, in the Th2 granulomas, other cell types produce VIP, which compensates for loss of macrophages as a source of this molecule.
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