Effect of pregnancy of cellular inflammation.

Pregnancy inhibits macrophage accumulation within the peritoneal cavity of Wistar rats when inflammation is induced by phytohaemagglutinin (PHA). The inhibition of macrophages was considerably greater than that of polymorphonuclear leucocytes (PMNs) induced by sodium caseinate. Pregnancy did not significantly alter macrophage accumulation to PHA injected into the pleural space or to nitrocellulose filters placed s.c. Cell-free homogenates prepared from the products of conception, but not normal liver, contained an anti-flammatory factor which, when injected i.v., inhibited macrophage accumulation to peritoneal but not to pleural or s.c. irritants. The responsible anti-inflammatory factor was identified as a peptide of mol. wt less than 1000.