Induction of IL-3 and granulocyte-macrophage colony-stimulating factor by substance P in bone marrow cells is partially mediated through the release of IL-1 and IL-6.

Experimental data strongly suggest that the nervous and immune systems are interrelated. One example of this interrelation is anatomical and is represented by innervation of the lymphoid organs by substance P (SP) immunoreactive fibers, among others. Neurotransmitters/neuropeptides can exert functional receptor-mediated immunologic responses. SP binding to its receptor induces cytokine production in macrophages and T cells and stimulates IgG secretion from B cells. SP has also been associated with inflammation and other immune-mediated diseases such as arthritis. We have previously reported an in vitro stimulatory effect of SP on hematopoiesis that was mediated mostly by the induction of two relevant hematopoietic growth factors, IL-3 and granulocyte-macrophage-CSF (GM-CSF). In this study, we have shown that SP, through the carboxyl terminus, induces the production of IL-3 and GM-CSF in bone marrow mononuclear cells. This production requires de novo synthesis and is blocked by two different SP-R antagonists, spantide and CP-96,345-1. The induction of IL-3 and GM-CSF is partially mediated by IL-1 and IL-6, which are also produced by bone marrow mononuclear cells. Furthermore, the production of IL-3 and GM-CSF correlated with an accumulation of their respective steady state mRNAs. T cells found within the bone marrow are responsible for most of the induced IL-3. Because SP mediates the release of IL-1, IL-3, IL-6, and GM-CSF, all important hematopoietic regulators, by bone marrow cells, this study further suggests the possibility of a regulatory role of the nervous system in hematopoiesis mediated by neuropeptides such as SP.