Figure 5. A functional FR-β is expressed on monocytes isolated from the synovial fluids of patients with RA.

(A). FR-β expression on monocytes from the synovial fluid of patients with RA was examined by flow cytometry using PE-labled anti-CD14 and an antibody (m909) against FR-β. (B) Functional FR-β is expressed selectively on CD14^highCD16⁻ but not CD14^int/lowCD16⁻ monocytes of synovial fluid from patients with RA. Moreover, neither lymphocytes nor granulocytes (defined by light-scatter) expressed a functional FR-β. To demonstrate that FOG binding is FR-mediated, similarly labeled cells were evaluated in the presence of 1000-fold molar excess of free folic acid (dashed lines) to block all folate-specific sites.