Production of placental protein 5 (PP5) by non-malignant human fibroblasts in culture. Comparison with 'pregnancy-specific' glycoprotein (SP1).

Placental protein 5 (PP5) was detected by radioimmunoassay in the culture media from 11/19 (58%) of cell lines derived from non-malignant human fibroblasts. One line was studied in detail. Its rate of PP5 secretion was polyphasic, with maxima of 3.1 pmol/10(6) cells per 24 h on day 1, 1.7 on day 8 and 2.0 on day 14, and minima of 0.9 on day 4, 1.0 on day 10 and 0.7 on day 15 of culture. A discordance with the secretion of pregnancy-specific glycoprotein (SP1) was demonstrated; the SP1 concentration was constant initially at 2.9 pmol/10(6) cells per 24 h, followed by a steady decrease to 0.5 on day 15. A small amount of PP5 was retained in the cells, but usually less than 5% of that secreted. When the culture medium was changed daily, more PP5 and SP1 were produced than when the cells were grown in conditioned media. A cell line derived from a human fibrosarcoma produced SP1 at rates exceeding that of the normal fibroblasts, but PP5 production was not detected in the fibrosarcoma.