Inhibitory effects of anti-rheumatic agent T-614 on immunoglobulin production by cultured B cells and rheumatoid synovial tissues engrafted into SCID mice

Objective. To clarify the pharmacological action of an anti-rheumatic agent T-614, we investigated its effects on immunoglobulin (Ig) production by cultured B cells and Ig secretion from synovial tissues of patients with rheumatoid arthritis (RA) using SCID mice engrafted with human RA tissue (SCID-HuRAg). Methods. Murine B cells were prepared from mouse spleen by a T-cell depletion method. The cells were cultured with lipopolysaccharide (LPS) and/or interleukin 4 (IL-4) in the absence or presence of T-614. Human B cells were isolated from peripheral blood of healthy donors and the Ig production was induced by co-culture with autologous T cells and anti-CD3 antibody. SCID-HuRAg was prepared according to our previous method. T-614 was orally administered to the mice once daily for 4 weeks starting on the fourth week after the implantation. Then, peripheral blood was obtained and the implanted tissues were removed. Igs in the culture media or the sera were determined by enzyme-linked immunosorbent assay (ELISA). Results. In murine B-cell cultures, T-614 significantly decreased not only the IgM production stimulated with LPS but IgG1 production induced by LPS and IL-4. Regarding human B cells stimulated with T cells, it also inhibited IgM and IgG production. In SCID-HuRAg mice, high concentrations of polyclonal human IgG were detectable in the sera of all mice. A significant decrease in the IgG level was observed in the T-614-treated group compared with the control group. Conclusions. We showed that T-614 inhibited Ig production by the cultured B cells and also decreased the high level of human IgG observed in SCID-HuRAg mice. These results may support its effect on plasma Ig in RA atients and provide insights into the mechanisms of its anti-rheumatic effect.