Mechanism by which adult mouse peritoneal macrophages affect neonatal suppressor cell activity

Suppressor cell activity is high in the spleen of newborn mice. The injection of adult mouse peritoneal exudate macrophages into newborn mice decreases the neonatal suppressor cell activity. Peritoneal exudate cells from thioglycollate and proteose-peptone pretreated adult mice are effective. Blocking the Fc-receptor on thioglycollate-induced macrophages eliminates their ability to reduce the neonatal suppressor cell activity. Peritoneal exudate cells from Corynebacterium-parvum-pretreated adult mice are not effective. The macrophage cell line, P388, also fails to decrease neonatal suppressor cell activity. A soluble macrophage factor, possibly Interleukin-1, is involved in the interaction between macrophages and suppressor cells. Stimulation of endogenous neonatal macrophage production with thioglycollate does not affect suppressor cell activity. The results are interpreted in the light of the hypothesis that a gradual increase in the number and/or function of macrophages after birth, results in a gradual decrease in suppressor cell activity, allowing for immunocompetence to emerge.