Induction of natural autoantibody activity following treatment of human immunoglobulin with dissociating agents

Treatment of normal polyclonal human IgG and of F(ab')(2) fragments of IgG with 6.0 M urea, 1.3 M sodium thiocyanate or with acidic buffers (pH 2.0), resulted in a dramatic and selective enhancement of the preexisting antibod y reactivity with self antigens. Enhanced antibody activity revealed by the dissociating agents was inhibited by the addition of an excess of the rele vant soluble antigen. Human monoclonal IgG, including four different IgG1m( 1) V(H)3+ and V(K)3+ paraproteins differing only in their CDRs, exhibited d ifferent changes in reactivity following urea treatment indicating major in volvement of CDR sequences. The calculated dissociation constant of the bin ding reaction of normal IgG to the self antigen actin was 10(-6) M, whether IgG had been treated or not, indicating that the treatment increased the p roportion of available self-reactive molecules instead of increasing the af finity of the preexisting natural autoantibodies. Enhanced autoreactivity w as not due to aggregation of Ig, unmasking of the antibody site by removal of low MW antigens, nor to the denaturation of natural Id-anti-Id complexes . Taken together, these results suggest that treatment of Ig with dissociat ing agent results in the exposure of basic polyreactive antibody structures . The enhancement of reactivity may be of relevance in physiology of mucosa l immunity and in therapeutic immunomodulation. (C) 2001 Academic Press.