Inhibition of Lymphocyte Proliferation by Uterine Fluid from the Pregnant Ewe1

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Abstract
Immunosuppressive molecules in uterine fluid from the nonpregnant uterine horn of unilaterally pregnant ewes at Days 60, 100, and 140 of gestation were examined. Uterine fluid from all days inhibited [3H]thymidine incorporation into phytohemagglutinin-stimulated lymphocytes. Inhibitory activity increased with advancing gestation. Uterine fluid also inhibited lymphocyte proliferation caused by other mitogens or by mixed lymphocyte reactions. Inhibitory activity was found in both salt volume (Mr < 1000) and void volume (Mr > 5000) fractions of uterine fluid resolved by Sephadex G-25 desalting columns. Only activity in the void volume was sensitive to pronase. Several fractions containing inhibitory activity were resolved when dialyzed uterine fluid was fractionated into acidic and basic components by cation-exchange chromatography and further resolved by gel filtration using Sepharose CL-6B. The most active fractions (inhibition/.mu.g protein) for both acidic and basic components eluted at the void volume of Sepharose CL-6B (Mr > 4 .times. 106). The inhibitory factor in the basic component that eluted at the void volume of Sepharose CL-6B was rich in carbohydrate, slightly cytotoxic, and partially sensitive to digestion with trypsin or oxidation with periodate. In conclusion, uterine fluid of unilaterally pergnant ewes is enriched in molecules that inhibit lymphocytes proliferation in vitro. Among these are low molecular weight, non proteinaceous factors and a very high molecular weight (Mr 4 .times. 106) fraction that contains protein and carbohydrate.