Detection of substance P and its receptor in human fetal microglia.

Substance P, the most abundant neurokinin in the CNS, is a major modulator of the immune system. We have examined the gene expression of substance P and its receptor in human fetal brain microglia. Using reverse transcription-polymerase chain reaction and Southern blotting assay, the four isoforms of preprotachykinin-A gene transcripts (alpha, beta, gamma and delta) were detected in the microglia. The human fetal microglia produced significantly higher levels of endogenous substance P protein (640-850 pg/10(6) cells) than did human peripheral blood monocyte-derived macrophages (25-50 pg/10(6) cells), as determined by an enzyme immunoassay. Using immunohistochemical staining with an anti-substance P antibody, cell membrane substance P immunoreactivity was observed. In addition, we identified the presence of messenger RNA for neurokinin-1 receptor, a primary receptor for substance P in human fetal microglia.From these data, we propose that substance P and its receptor are biologically involved in regulating the functions of microglia, and potentially play an important role in host defense of the central nervous system.