Substance P does not alter interleukin-1 expression by splenic or granuloma macrophages in murine schistosomiasis

Substance P (SP) is an undecapeptide with neurotransmitter and immunoregulatory properties. In murine schistosomiasis, ova naturally induce liver and intestinal granulomas. These granulomas contain macrophages, and eosinophils that produce SP. A report showed that human blood monocytes isolated by adherence release interleukin-1 (IL-1) in response to SP (Lotz et al. (1989) Science 241, 1218). IL-1 is important for initiation of hypersensitivity granulomas. Therefore, it was determined whether SP modulates granuloma macrophage IL-1 production in murine schistosomiasis. Macrophages were obtained from lung and liver granulomas, and from spleens of infected mice. A thymocyte proliferation assay measured IL-1 activity in culture supernatants. Total RNA, extracted from macrophages, was assayed for IL-1 alpha and beta mRNA by Northern blotting using cDNA probes. In response to lipopolysaccharide (LPS), splenic macrophages and macrophages from young lung granulomas released appreciable IL-1. Macrophages from liver granulomas, that were lesions older than the lung granulomas, were unresponsive to LPS with regard to IL-1 secretion. Yet, granuloma macrophages spontaneously expressed IL-1 alpha and beta mRNA. LPS enhanced IL-1 mRNA expression in both splenic and granuloma macrophages. Exposure of macrophages from all sources to SP did not alter IL-1 secretion or gene expression. Similarly, the responsiveness of macrophages to LPS was not affected by concomitant exposure to SP. It is concluded that, in the murine system, SP does not directly influence splenic or granuloma macrophage IL-1 secretion or gene expression. Also, it appears that macrophage secretion of IL-1 is rapidly down-regulated following granuloma elicitation.