Capsaicin-induced inhibition of mitogen and interleukin-2-stimulated T cell proliferation: its reversal by in vivo substance P administration.

The direct and indirect interaction between the nervous and the immune systems was evaluated in the rat using the neurotoxin capsaicin. Capsaicin treatment of neonatal rats (50 mg/kg at 2 days of age), results in a marked inhibition of mitogen and hrIL-2-induced cell proliferation both in the spleen and peripheral blood. Inhibition is already evident on day 15 after treatment and persists until day 90 in the spleen; at this time a return to control levels is observed in peripheral blood. The inhibition of proliferative response strongly correlates with a decreased number of CD5+ and CD4+ T cells as evaluated by immunofluorescence and FACS analysis. Moreover, continuous in vivo SP administration stimulates mitogen and hrIL-2-induced proliferative response and completely reverts the capsaicin-induced inhibition of lymphocyte proliferation in the spleen.