The neuropeptide substance P does not influence the migration of B, T, CD8+ and CD4+ ('naive' and 'memory') lymphocytes from blood to lymph in the normal rat.

Thoracic duct lymphocytes (TDL) continuously patrol through the body, facilitating immune responses at most sites. The neuropeptide Substance P might regulate immune responses by influencing the migration of TDL. Therefore, it was investigated whether Substance P affects the migration of thoracic duct B, T, CD8+ and CD4+ ('naive' and 'memory') lymphocytes from blood to lymph in vivo. Labelled TDL were either incubated with Substance P and then injected into normal rats, or incubated without Substance P and then injected into rats continuously receiving Substance P intravenously. The numbers of labeled B, T, CD8+ and CD4+ ('naive' and 'memory') lymphocytes were determined in blood and thoracic duct lymph for 1 and 5 days, respectively. Neither the in vitro incubation with Substance P nor its in vivo application influenced the disappearance of any lymphocyte subset from the blood or its reappearance in the lymph. In addition, continuous intravenous application of the Substance P antagonist CP 96.345 did not alter the volume or the lymphocyte number of the efferent lymph. The present study indicates that the nervous system does not influence immune responses via Substance P by altering the migration pattern of B, T, CD8+ and CD4+ ('naive' and 'memory') lymphocytes.