Interaction of Bovine Uterine Luminal Protein with Interleukin-2 and the Interleukin-2 Receptor of T Lymphocytes1

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Abstract
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 .alpha. chain (Tac protein) of the IL-2R of HLC. High- and low-molecular weight (Mr) ULP components (H-ULP > 248,000 Mr and L-ULP 21,000 Mr, 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 .beta. chain) of HLC, H-ULP failed (p > 0.05) to bind to the p55 .alpha. 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 .times. 106 Mr) 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.