OBJECTIVE Gamma-interferon (gamma-IFN) has been shown to be a potent inhibitor of collagenous protein production independent of its effects on noncollagenous protein production and cell proliferation in vitro. To understand further the processes controlling tissue fibrosis and the potential use of gamma-IFN as an antifibrotic treatment after glaucoma filtering surgery, the in vitro effects of recombinant gamma-IFN on procollagen mRNA production were studied. METHODS Subconfluent human Tenon's capsule fibroblast cultures were exposed to 10, 50, 500, and 1000 U/ml of human recombinant gamma-IFN for 48 hours and to 500 U/ml for 12, 24, and 72 hours. After the incubation period, polyA+ mRNAs were isolated by oligo (dT) cellulose columns, separated according to size by electrophoresis through a denaturing agarose gel, and transferred to an activated nylon membrane for Northern blot analysis. The levels of type III (alpha 1) procollagen, type I (alpha 1) procollagen, and fibronectin (noncollagenous protein) mRNA were determined by hybridization with radiolabeled cDNA probes specific for these components followed by autoradiography. RESULTS Densitometric analysis showed gamma-IFN selectively inhibited type III and type I procollagen mRNA synthesis from 24% (10 U/ml) to 99% (1000 U/ml) while leaving fibronectin mRNA synthesis unaffected. The degree of inhibition was also time dependent; more inhibition occurred with increasing incubation time. CONCLUSIONS These results indicate that gamma-IFN is able to regulate collagen synthesis at the transcriptional level and that its inhibition is relatively specific. Gamma-interferon's specific inhibitory effects may offer advantages over current therapies in modulating the fibrotic response after glaucoma filtering surgery.