INTERACTION OF BOVINE UTERINE LUMINAL PROTEIN WITH INTERLEUKIN-2 AND THE INTERLEUKIN-2 RECEPTOR OF LYMPHOCYTE-T

Bovine uterine luminal proteins (ULP) collected on Day 17 of pregnancy were tested for inhibition of binding of interleukin-2 (IL-2) to the IL-2 receptor (IL-2R) of bovine (CLC) and human (HLC) T lymphocytes and for binding to IL-2. Additional experiments assessed IL-2 binding to the p55 α chain (Tac protein) of the IL-2R of HLC. High- and low-molecular weight (M(r)) ULP components (H-ULP > 248 000 M(r) and L-ULP 21 000 M(r), respectively) inhibited (p < 0.05 and 0.01, respectively) the binding of 125I-IL-2 to the IL-2R of CLC, whereas only H-ULP inhibited (p < 0.05) binding to the IL-2R (presumably, the p75 β chain) of HLC. H-ULP failed (p > 0.05) to bind to the p55 α chain of the IL-2R of HLC. For IL-2 binding, L-ULP failed (p > 0.05) to bind 125I-IL-2 in short (2 h)-term and long (45 h)-term experiments, whereas binding was evident (p < 0.05) for H-ULP at 2 h of incubation. For H-ULP, mean (±SEM) percentages for bound and unbound 125I-IL-2 were 70.1 ± 11.4 and 29.9 ± 11.4, respectively. Further purification of H-ULP yielded a component (1.76 x 106 M(r)) that bound 11.7% of 125I-IL-2 and inhibited (p < 0.01) thymidine uptake and binding of 125I-IL-2 to the IL-2R of CLC. H-ULP-mediated suppression of lymphocyte proliferation may result from blocking IL-2R recognition of IL-2 as well as binding to IL-2, whereas suppression by L-ULP may predominantly result from blocking IL-2R.