Biology of Reproduction, Vol 19, 15-25, Copyright © 1978 by Society for the Study of Reproduction

Suppression of Lymphocytes in vitro by Porcine Uterine Secretory Protein

¹ Department of Animal Science, Ohio Agricultural Research and Development Center, Wooster, Ohio 44691

The effects of porcine uterine secretory porteins upon peripheral blood lymphocyte response to a mitogen and xenogeneic cells was investigated in a series of in vitro culture experiments. Porcine lymphocytes were obtained by use of Ficoll-Paque and were cultured in RPMI 1640 containing 10% fetal calf serum, 2% extra glutamine and antibiotics (100 IU penicillin/ml, 100 µg streptomycin/ml and 0.25 µg fungizone/ml). The cells were treated with varying concentrations of uterine protein preparations or control proteins. Stimulators of the lymphocytes were phytohemagglutinin (PHA), sheep lymphocytes or mitomycin C-treated sheep lymphocytes. The response of the porcine lymphocytes to the stimulator was determined by incorporation of [³H]-thymidine. At the end of a 72 h culture period, the cells were harvested onto cellulose-triacetate membrane filters and the incorporated radioactivity was determined by liquid scintillation counting. Parallel cultures to determine cell viability were carried out in each experiment. Day 15 porcine uterine flushings (pUF) suppressed lymphocyte response to all stimulants, while Day 8 pUF had no effect in the same concentration range. Bovine serum albumin and porcine serum had no significant effect. A fraction of Day 15 pUF containing small acidic proteins was 5-10 times more suppressive at the same dose level than unfractionated Day 15 pUF. The correlations of log concentration of both pUF and the active fraction with lymphocyte suppression were highly significant (P<0.001). The suppressive activity was noncytotoxic and reversible. Results of experiments with cells as stimulants and PHA as a stimulant were similar. Thus, small acidic proteins (approximately 15,000 d) secreted during the period of implantation in the pig are suppressive to pig lymphocytes in vitro. This phenomenon may prove to be important in the maternal-fetal relationship in vivo.