SUBSTANCE-P ENHANCES THE SECRETION OF TUMOR-NECROSIS-FACTOR-ALPHA FROM NEUROGLIAL CELLS STIMULATED WITH LIPOPOLYSACCHARIDE

The neuropeptide, substance P (SP), can stimulate secretion of TNF-alp ha from macrophages. Neuroglia have SP receptors and subserve various macrophage-like functions in the central nervous system. We investigat ed whether SP stimulates secretion of TNF-alpha from primary cultures of neuroglial cells containing both astrocytes (approximately 90%) and microglia (approximately 10%). SP alone had no effect; however in the presence of LPS (10 ng/ml), SP (1 to 10 nM) caused a dose-dependent i ncrease in TNF-alpha secretion above the level measured in response to LPS alone. The effective doses of SP correlated with I-125-labeled Bo lton Hunter-conjugated SP binding (K(d) 0.2 nM) to these cultures. Inc ubation with LPS did not change the number or affinity of SP-binding s ites. In cultures enriched for microglia (>99% pure), LPS stimulated t he secretion of TNF-alpha but SP caused no enhancement. Microglia have no detectable I-125-labeled Bolton-Hunter-conjugated SP binding sites in the presence or absence of LPS. These results indicate that the ac tion of SP is mediated through astrocytes. We investigated whether IL- 1 mediates the SP enhancement of TNF-alpha. secretion. Addition of IL- 1 -neutralizing antisera to mixed cultures stimulated with both LPS an d 10 nM SP decreased TNF-alpha secretion to the level observed with LP S alone. LPS alone stimulated the secretion of IL-1 in a dose-dependen t manner in the primary cultures, and this LPS-mediated IL-1 secretion was enhanced by SP. This enhancement was not observed in microglial c ultures. SP may therefore play a role in neuropathologies in which the se cytokines have been implicated.