CD40LG and systemic lupus erythematosus: Interestingly, anti-dsDNA titer correlated negatively with both isotype anti-PC antibodies (IgM: r = −0.508, p = 0.019; IgG: r = −0.460, p = 0.036) and with total IgM (r = −0.501, p = 0.021) but not IgG (r = 0.065, p = 0.780) levels, thus suggesting a detrimental effect of SLE disease activity on naturally occurring protective IgM antibodies.