Structural diversity of the fibroblast-activating factors generated by human blood monocytes and U937 cells

The incubation of purified human blood monocytes with phytohemagglutinin (PHA) and of cultured U937 human monocyte-like cells with phorbol myristate acetate (PMA) evoked the generation of fibroblast-activating activity, as assessed by stimulation of the uptake of [3H]thymidine by human dermal fibroblasts. Filtration of the supernates from monocytes and U937 cells on Sephadex G-75 resolved fibroblast-activating factors of m.w. 25,000 to 40,000, designated FAF-M and FAF-U937, respectively, from smaller factors of an apparent m.w. of approximately 10,000. FAF-M and FAF-U937 were acidic by isoelectric focusing with respective pI values of 4.0 to 5.2 and 5.4 to 5.6. The smaller factors from both sources filtered on Sephadex G-25 in phosphate-buffered saline with an apparent m.w. of 10,000. However, filtration of the same factors on Sephadex G-25 in 0.1 M acetic acid revealed one predominant fibroblast-activating activity for each cell source of an apparent m.w. of 500 to 1000. The 500 to 1000 dalton factors were inactivated by treatment with trypsin and subtilisin, suggesting that the activity was attributable to fibroblast-activating peptides, termed FAP-M and FAP-U937. FAP-M and FAP-U937 each appeared to be composed of a predominant hydrophilic activity by reverse-phase high-performance liquid chromatography. Human blood monocytes and U937 monocytes both produce structurally diverse fibroblast-activating proteins and peptides, which may contribute to the immunologic regulation of wound healing and fibrosis.