Genetically‐restricted effector molecules released by human lymphocytes in response to early pregnancy factor

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Abstract
The binding of early pregnancy factor (EPF) to lymphocytes stimulates the release of soluble effector molecules. Studies in mice have shown that it is these factors rather than EPF as such which are inhibitory in the T cell-dependent reactions, the adoptive transfer of contact sensitivity and the rosette inhibition test. Two factors have been identified: mEPF-S1 (Mr 15 000) is major histocompatibility complex (MHC)-restricted while mEPF-S2 (Mr 55 000) is restricted to a locus (or loci) outside the MHC. In the present paper, evidence is presented which shows that EPF also induces the release of soluble mediators from human lymphocytes. With the rosette inhibition test two factors have been detected, both of similar size and genetic restriction to those described previously in the mouse. One factor, designated hEPF-S1 (Mr 14-18 000), is human lymphocyte antigen (HLA)-restricted and the other, hEPF-S2 (Mr 50-60 000), appears to be restricted to a locus (or loci) outside the HLA complex.