Immunosuppressive effect of uterine secretory protein from Angus and Brahman cows upon lymphocytes in vitro

Uterine luminal protein collected on d 17 (estrus = d 0) from Angus (n = 20) and Brahman (n = 19) cows of varying reproductive status was evaluated for immunosuppressive activity in vitro. Reproductive status consisted of the following categories: nonpregnant (uterine flushing was devoid of embryonic material); remnant (uterine flushing contained obvious degenerative fragments of embryonic tissue) and pregnant (uterine flushing contained an intact conceptus). Uterine protein was tested for suppressor activity in both phytohemagglutinin (PHA) and mixed lymphocyte culture (MLC) systems. Incorporation of [3H]-thymidine into 1 X 10(6) Angus or Brahman lymphocytes for PHA cultures and 5 X 10(5) lymphocytes from each breed for MLC experiments served as the index for lymphocyte blastogenesis. For all experiments, uterine luminal protein from nonpregnant, remnant and pregnant Angus and Brahman cows suppressed (P less than .01) lymphocyte blastogenesis for Angus and Brahman lymphocytes, respectively. In two lymphocyte-uterine protein specificity experiments containing PHA, uterine protein from Angus cows suppressed (P less than .01) blastogenesis of Brahman lymphocytes and uterine protein from Brahman cows suppressed (P less than .01) blastogenesis of Angus lymphocytes. Within and between breed comparisons of suppressor activity were evaluated when expressing uterine protein culture data as percentages of control (no test protein) cultures. At 200, 400 and 800 micrograms/ml of uterine protein, suppressor activity was consistently greater in secretions from pregnant than from nonpregnant cows for each breed. For between breed comparisons, there were nonsignificant trends toward greater suppressor activity for nonpregnant Angus than for nonpregnant Brahman cows at 200, 400 and 800 micrograms/ml of protein. Suppressor activity was greater (P less than .10) for pregnant Angus than for pregnant Brahman cows at 400 micrograms/ml of protein and tended to be greater for pregnant Angus than for Brahman cows at 800 micrograms/ml of protein. These data indicate that uterine secretory protein collected on d 17 from Angus and Brahman cows exerted immunosuppressive activity in vitro. Further, suppressor activity in each breed was greater in pregnant than in nonpregnant cows and suppressor activity tended to be greater for Angus than for Brahman cows.