Characterization of human fibroleukin, a fibrinogen-like protein secreted by T lymphocytes.
We have recently cloned the human homologue of the murine pT49 cDNA (hpT49h), a transcript encoding a protein homologous to the beta- and gamma-chains of fibrinogen. Here, we report the identification of the hpT49h gene product using mAbs generated against a peptide corresponding to the carboxyl-terminal end of the deduced protein and a recombinant protein fragment expressed in Escherichia coli. mAbs 23A6, 7B12, and 3F4 specifically recognized a protein of 70 kDa in reducing SDS-PAGE in the culture supernatant of 293T cells transiently transfected with the full length hpT49h cDNA and freshly isolated PBMC. Under nonreducing conditions, the material migrated with a molecular mass of 250 to 300 kDa, indicating that the 70-kDa protein forms a disulfide bonded complex. Because of its homology with fibrinogen, we have termed this protein fibroleukin. Fibroleukin is spontaneously secreted in vitro by freshly isolated CD4+ and CD8+ T lymphocytes. RT-PCR analysis revealed preferential expression of fibroleukin mRNA in memory T lymphocytes (CD3+/CD45R0+) compared with naive T lymphocytes (CD3+/CD45RA+). Fibroleukin production by PBMC was rapidly lost in culture. Production could be partially maintained in the presence of IFN-gamma, while T lymphocyte activation had no effect. To demonstrate fibroleukin production in vivo, we analyzed colon mucosa by immunohistology. Fibroleukin staining was detected in the extracellular matrix of the T lymphocyte-rich upper portion of the lamina propria mucosa. While the exact function of fibroleukin remains to be defined, these data suggest that fibroleukin may play a role in physiologic lymphocyte functions at mucosal sites.
Marazzi
S
S
Centre Pluridisciplinaire d'Oncologie, School of Medicine, University of Lausanne, Switzerland.
Blum
S
S
Hartmann
R
R
Gundersen
D
D
Schreyer
M
M
Argraves
S
S
von Fliedner
V
V
Pytela
R
R
Rüegg
C
C
D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal / Q000096:biosynthesis; D017252:CD3 Complex / Q000032:analysis; D015704:CD4 Antigens / Q000032:analysis; D018414:CD8-Positive T-Lymphocytes / Q000378:metabolism; D002460:Cell Line; D002478:Cells, Cultured; D003106:Colon / Q000378:metabolism; D004220:Disulfides / Q000378:metabolism; D005340:Fibrinogen / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D015870:Gene Expression / Q000276:immunology; D006801:Humans; D007156:Immunologic Memory; D007399:Interphase / Q000276:immunology; D007413:Intestinal Mucosa / Q000378:metabolism; D007668:Kidney / Q000166:cytology; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000096:biosynthesis; D016176:T-Lymphocyte Subsets / Q000737:chemistry / Q000276:immunology / Q000378:metabolism*
D000911:Antibodies, Monoclonal; D017252:CD3 Complex; D015704:CD4 Antigens; D004220:Disulfides; C095202:FGL2 protein, human; D046911:Macromolecular Substances; D012333:RNA, Messenger; D005340:Fibrinogen