CD40LG and systemic lupus erythematosus: Although IgM deficiency has not been consistently reported as being a risk factor for SLE development, note the following three details: (a) observations in murine models indicate that IgM autoantibodies may be protective as neutralizers of IgG autoantibodies; (b) deficiencies in serum and/or secretory IgM resulted in elevated levels of lupus-type IgG antibodies; and (c) these clinical cases all support the idea that a lack of IgM production may be relevant to SLE pathophysiology [reviewed in Ref.