Biochemical characterization of PRL-immunoreactive peptide in the BMSC supernatants. Supernatants of resting (lane 5), PAF-stimulated (lane 6), WEB 2170 plus PAF stimulated (lane 7) BMSC; positive control IM9-P3 (lane 8) and negative control Hep-G2 (lane 9) cell lines were immunoprecipitated with rabbit-antihuman PRL antiserum (IC-5) and run on SDS-PAGE. Decreasing amounts (100, 50, 25, 12.5 ng) of standard human PRL (NIDDK) (lanes 1 through 4) were also run. Filters were blotted with two anti-PRL MoAbs direct against distinct epitopes and the reactivity revealed by peroxidase conjugated Protein A and chemiluminescence. No signal was observed when human PRL (100 ng) and supernatant of IM9-P3 were immunoprecipitated with control serum (not shown).