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