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Fibrin plays important roles in the wound healing processes, including blood clotting and platelet aggregation. Additional activities of fibrin were found in this study, which utilizes human THP-1 cells treated 1,25-(OH)2 vitamin D3 and plasminolytic fragments derived from fibrin. Coated fibrin fragment E on culture plates induced cell adhesions and morphological changes of the THP-1 cells, being resembled to tissue macrophages. Morphological changes of the THP-1 cells were caused by microfilament reorganization. IL-1β production was increased in the THP-1 cells by adherent fibrin fragment E, but not by fibrin fragment D or by fibrinogen fragment E. The elevation of IL-1β production is caused by transcriptional activation. Incubation with cytochalacin D, an actin polymerization inhibitor, prevents both microfilament reorganization and morphological changes, but has no effect on the IL-1β production stimulated by fibrin fragment E. This data suggests that the IL-1β production in the THP-1 cells do not require microfilament reorganization and integrin aggregation. Taken together, these results indicate that fibrin matrix plays an additional role in the stimulation of monocytes for production of IL-1β, morphological changes and cell adhesion, resulting in the facilitation of the wound healing processes. [ABSTRACT FROM AUTHOR]