The Cytotoxic T Lymphocyte Gene FIBLP with Homology to Fibrinogen β and γ Subunits Is Also Induced in Mouse Macrophages by IFN-γ

To identify genes induced in mouse macrophages by IFN-γ a cDNA subtraction library of IFN-γ-induced genes was screened. One of the clones, 36F2, was identified by DNA sequencing as the FIBLP gene. The FIBLP (fibrinogen-like protein) gene is a T-lymphocyte-specific gene that is expressed in mouse cytotoxic T lymphocytes but not in helper T lymphocytes or B lymphocytes. The protein sequence shows a high homology to fibrinogen β and γ subunits. The FIBLP gene is not expressed in unstimulated mouse peritoneal macrophages but is induced by IFN-γ to high levels. FIBLP mRNA is detected by 1 hr after the addition of IFN-γ and maximal levels are reached by 12 hr. Expression of FIBLP mRNA was not induced by IL-2, IL-4, IL-10, or TNF-α. Though the function of this gene is unknown, its expression in both cytotoxic T lymphocytes and activated macrophages suggests that FIBLP may play an as yet undefined role in the cytotoxic function of these cells.