Immunosuppressive Effect of Ovine Uterine Secretory Protein upon Lymphocytes in vitro12

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Abstract
The immunosuppressive effect of ovine uterine protein upon phytohemagglutinin (PHA)-stimulated peripheral blood lymphocytes was investigated in vitro. Uterine secretory protein was collected and concentrated in sheep uterine flushings (SUF) obtained from nonpregnant and pregnant Dorset ewes on Days 4, 9, and 14 of the cycle. Varying concentrations of protein (2.5-1600µ g/ml) were added to cultures each containing 1 x 106 ovine lymphocytes and 0.6 µg of PHA. Lymphocyte response to PHA was suppressed in cultures containing SUF protein from Day 4, 9, and 14 nonpregnant and pregnant ewes. The regression of SUF protein concentration with lymphocyte suppression (as percent of control) for each day and reproductive stage was significant (P<0.001). Almost complete suppression occurred with much less SUF protein (100 µg/ml) obtained on Day 14 of pregnancy than was obtained at most other times (1600 µg/ml). Ovine serum and bovine serum albumin had no significant immunosuppressive effect. The immunosuppressive effect of SUF protein was not mediated by cytotoxicity.