Inhibition of B-cell activation by retinal pigment epithelium.

PURPOSE To determine whether retinal pigment epithelial (RPE) cells can inhibit B-cell activation in vitro. METHODS Primary cultured RPE cells were established from normal C57BL/6 mice. Activated target B cells were established from splenic B cells stimulated with anti-mouse CD40 antibody and lipopolysaccharide (LPS) in the presence of recombinant interleukin 4 (rIL-4). B-cell activation was assessed by examining proliferation through [(3)H]-thymidine incorporation or carboxyfluorescein succinimidyl ester dilution, and antibody production was determined by ELISA. Expression of costimulatory molecules and the receptors on B cells was evaluated by flow cytometry. Neutralizing anti-TGFβ antibodies were used in the assay. RESULTS Addition of primary cultured RPE cells suppressed B-cell proliferation in response to anti-CD40, LPS, and rIL-4 stimulation. Similarly, antibody production by these activated B cells was suppressed. Suppression of B-cell activation was mediated by a soluble factor because supernatants from cultured RPE cells were sufficient to inhibit B-cell responses. Moreover, TGFβ was identified as the soluble mediator given that RPE-supernatants failed to suppress B-cell activation if pretreated with neutralizing anti-TGFβ antibodies. CONCLUSIONS Cultured RPE cells suppress the activation of B cells in vitro. These data support the hypothesis that retinal pigment epithelium has immunosuppressive properties that are capable of suppressing B-cell activation.