C3 synthesis and CRs expression during differentiation of a murine stem cell line

C3 production, release and CRs expression during the neutrophilic different iation of a murine non tumorigenic cell line is investigated. The murine no n tumorigenic cell line 32DCl3(G) which undergoes terminal differentiation into polymorphonuclear granulocytes when cultured in presence of G-CSF was selected as a suitable in vitro model for this study. The results show that as the cells progress into the differentiation program, levels of C3 mRNA increase, accompanied by increased C3 production. As differentiation progre sses the cells gradually express CRs on their surface; these are undetectab le on the surface of undifferentiated cells. As a consequence of CRs appear ance, cells become able to bind C3 through receptorial binding. Differences were found in the modality of C3 secretion: differentiated cell s tend to store C3 in their intracellular compartments rather than secrete it continuously into the medium and they respond to membrane stimulation wi th increased secretion of C3. Treatment of 32DCl3(G) with TNF-alpha increased C3 production in a time- an d dose-dependent fashion. Cell response to this stimulus progressively incr eases during the differentiation process suggesting that they acquire funct ionality in the signal transduction mechanisms.