Tachykinin-mediated modulation of the primary antibody response in rats: evidence for mediation by an NK-2 receptor.

Evidence for the involvement of primary afferent nerves and their associated neuropeptides in in vivo immunologic responses has been based on experiments in rats in which destruction of primary afferent nerves by the sensory neurotoxin capsaicin results in a diminished ability of the animal to mount a primary antibody response to sheep red blood cell (SRBC) antigen. This effect was shown to be reversed by substance P infusion immediately following antigenic stimulation. In this report we show that neurokinin A (NKA) is 12 times more potent than substance P in its capacity to reverse the effects of neonatal capsaicin pretreatment on the antibody response. Neurokinin A has a pD2 of 6.65 compared to 5.98 for substance P. In addition, NKA was more potent than substance P in reversing the effects of surgical lesions 2 days prior to antigenic stimulation. The effects of the D- and L-Pro9 analogues of [Glp6, Pro9]-SP6-11 on the plaque-forming cell response in capsaicin-treated rats provide further support for the hypothesis that the tachykinin receptor modulating the primary antibody response is an NK-2 receptor. These results demonstrate, for the first time, a role for NKA in in vivo immunomodulation.