Objective: To define the distribution of folate receptor beta (FRbeta)-expressing cells in various tissues, including rheumatoid arthritis (RA) synovial tissues, and to verify the effects of an immunotoxin composed of an anti-FRbeta monoclonal antibody (mAb) and truncated Pseudomonas exotoxin A (PEA) on apoptosis and tumor necrosis factor alpha (TNFalpha) production by adherent synovial mononuclear cells from RA patients.
Methods: Anti-FRbeta mAb were produced by immunizing mice with FRbeta-transfected murine pre-B cells. The distribution of the FRbeta antigen was examined by immunohistochemical analysis using anti-FRbeta mAb and macrophage-specific anti-CD163 mAb. Anti-FRbeta mAb was chemically crosslinked with truncated PEA. FRbeta-expressing macrophages were produced by the transfection of adenovirus vector containing the FRbeta gene. Apoptotic cells were detected by staining with propidium iodide. TNFalpha was measured by enzyme-linked immunosorbent assay.
Results: FRbeta-expressing cells were not present in peripheral blood leukocytes and their activated cells. In all of the tissues examined, most FRbeta-expressing cells were CD163+. The immunotoxin significantly induced the apoptosis of FRbeta-transfected macrophages and adherent RA synovial mononuclear cells and inhibited TNFalpha production by adherent RA synovial mononuclear cells.
Conclusion: We demonstrated the limited distribution of FRbeta-expressing cells in various tissues. The immunotoxin targeting FRbeta-expressing cells will provide a therapeutic tool for rheumatoid synovitis.