Modulation of the in vitro lymphocyte response by rabbit blastocysts

Modulation by preimplantation (day 6 post coitum) rabbit blastocysts or by blastocoel fluid of the phytohemagglutinin (PHA)-stimulated autologous splenocytes as well as mixed leukocyte cultures (MLC) of rabbit allogenic splenocytes in vitro was studied. Results showed that in the absence of the blastocyst or blastocoel fluid, specific incorporation (S.I.) of PHA activated cultures was 7.11 +/- 1.19 (mean +/- S.E., n = 11), whereas the addition of 1 (n = 9), 2 (n = 8) or 3 (n = 7) blastocysts significantly (P less than 0.001) reduced the S.I. (0.56 +/- 0.09, 0.47 +/- 0.09 and 0.27 +/- 0.05, respectively). In the absence of the blastocysts or blastocoel fluid, 3057 +/- 1763 cpm were recorded as MLC response; the addition of 1 or 3 blastocysts showed 83 and 87% suppression, respectively (n = 11, P less than 0.001). The addition of blastocoel fluid also suppressed PHA or MLC responses (P less than 0.05). The effect was not due to the crowding or cytotoxic effects induced by the blastocysts in the cocultures, since spleen cell viability was greater than 89%. Rabbit blastocysts around the time of implantation have a great capacity of modulating PHA-induced splenocyte proliferative as well as allogenic recognition in vitro.