Endogenously produced substance P contributes to lymphocyte proliferation induced by dendritic cells and direct TCR ligation

Substance P (SP) is an immunoregulatory tachykinin which augments antigen- and mitogen-induced lymphocyte proliferation via signaling through the neur okinin-1 receptor (NK1-R). Non-neuronal cells of the immune system such as monocytes, T lymphocytes and eosinophils can be a source of SP. We have inv estigated if antigen-presenting dendritic cells (DC) produce SP. DC were gr own from bone marrow precursors using a cocktail of GM-CSF, IL-4 and Flt-3 ligand. Reverse transcriptase-PCR amplification using primers for the mouse preprotachykinin-A gene and direct DNA sequencing of amplified products fr om purified DC demonstrated the presence of the gamma-transcript of the gen e, coding for SP and neurokinin A. At the protein level, mouse DC expressed SP as determined by an enzyme immunoassay and confirmed by immunostaining. The functional role of endogenous SP release was determined. During the in teraction with syngeneic or allogeneic DC, the addition of a specific NK1-R antagonist partly reduced proliferation in responding T lymphocytes. This was confirmed by using responders derived from NK1-R-deficient mice. In the absence of DC, proliferation of T cells induced by direct TCR ligation and soluble CD28 was partly dependent on signaling through NK1-R, revealing an autocrine effect of SP production by T cells. In conclusion, these results demonstrate that endogenously produced SP contributes to T cell proliferat ion induced by DC or TCR/CD28 stimulation.