Deficiency in serum immunoglobulin (Ig)M predisposes to development of IgGautoantibodies

Serum immunoglobulin (Ig)M provides the initial response to foreign antigen and plays a regulatory role in subsequent immune response development, acc elerating the production of high-affinity IgG. Here we show that mice defic ient in serum IgM have: an increased propensity to spontaneous autoimmunity as judged by the development with age of serum IgG anti-DNA antibodies and the renal deposition of IgG and complement. They also exhibit augmented an tiDNA IgG production on exposure to lipopolysaccharide. Thus, deficiency in serum IgM leads to diminished responsiveness to foreign antigens but incre ased responsiveness to sell-a paradoxical association reminiscent of that d escribed in humans deficient in complement or IgA.