Regulation of leukocyte interleukin 2 and interleukin 2 receptor gene expression by rabbit blastocoelic fluid

The mechanisms underlying the inhibition of lymphocyte proliferative response by rabbit blastocoelic fluid collected on day 12 of embryonic development were investigated. Treatment with blastocoelic fluid, even in the presence of concanavalin A, maintains lymphocytes in a quiescent state by preventing cell entry into the S phase of the cell cycle. Gene expression of interleukin 2 receptor is completely blocked by treatment with blastocoelic fluid as are the secretion and gene expression of interleukin 2. Addition of interleukin 2 to prestimulated interleukin 2 receptor positive lymphocytes failed to downregulate the expression of high-affinity interleukin 2 receptor and completely abolished the embryonic fluid-mediated inhibitory effect on [3H]thymidine incorporation. Taken together, these results suggest that embryonic fluid has differential inhibitory effects, depending on the activation state of the lymphocytes. Nevertheless, inhibition of interleukin 2 and interleukin 2 receptor expression by embryonic fluid restrains immune cell activity and therefore can be implicated in the survival of the fetal semi-allograft.