OBJECTIVE

To investigate the immunopathological significance of CD40/CD40 ligand system for B cell hyperactivation in SLE patients, the expression and the function of CD40 on B cells were compared with those of normal controls.

METHODS

Expression of CD40 was evaluated by flow cytometry. DNA synthesis of B cells were measured by 3H - TdR incorporation. Antibody production was assessed by ELISA.

RESULTS

There was no significant difference between SLE and normal controls in CD40 expression on peripheral blood B cells. Recombinant CD40 ligand-leucine zipper fusion protein (CD40L-LZ) significantly enhanced 3H - TdR incorporation by both SLE and normal B cells (P<0.01). 3H - TdR incorporation of SLE B cells without stimuli (P<0.001) and with CD40L-LZ stimulation (P<0.05) were significantly lower in SLE patients compared with normal controls. Active SLE B cells spontaneously produced significantly larger amounts of total IgG than normal B cells (P<0.05). CD40L-LZ significantly increased the production of total IgG by SLE B cells (P<0.05), but not by normal B cells. Active SLE B cells spontaneously produced IgG anti-dsDNA and IgG anti-ssDNA antibodies. CD40L-LZ significantly increased the production of these autoantibodies by SLE B cells (P<0.05). B cells from normal controls do not produce these autoantibodies spontaneously nor in response to CD40L-LZ.

CONCLUSION

These findings indicate that signalling via CD40 plays an important role in B cell proliferation and autoantibody production in human SLE.