Anti-DNA and anti-platelet specificities of SLE-derived autoantibodies: evidence for CDR2H mutations and CDR3H motifs.
Although polyreactivity appears to be a characteristic feature of natural autoantibodies, polyreactive anti-DNA autoantibodies can be derived both from patients with autoimmune disease and from normal individuals. It is unclear whether these autoantibodies differ depending on their origin, but previous studies from our laboratory have suggested that polyreactive systemic lupus erythematosus (SLE)-derived platelet-binding anti-DNA autoantibodies have more restricted antigen reactivity and greater functional activity than normal-derived polyreactive autoantibodies. The objective of the present study was to characterize the VH and VL region sequences of 10 human hybridoma anti-DNA autoantibodies derived from peripheral blood lymphocytes of different origins [SLE, rheumatoid arthritis (RA), or normal] to determine whether there are structural differences between these autoantibodies. We show that although some unmutated germline structures (VH and VL) are represented, these are not restricted to anti-DNA autoantibodies from normal individuals and that two normal-derived anti-DNA antibodies showed quite extensively mutated VH genes. However, these mutations, unlike those found in the CDR2H of several of the SLE-derived antibodies, did not appear to be antigen-selected. Three different amino acid motifs, putatively involved in antigen binding specificity, were observed in the CDR3H segments of some of the autoantibodies. One was the previously described YYGSG motif, which was found in a normal-derived anti-DNA autoantibody, while two new potential motifs were observed only in SLE-derived platelet-binding anti-DNA autoantibodies. These data suggest that antigenic and functional differences between SLE-derived and normal-derived platelet-binding anti-DNA autoantibodies may be due to antigen-selected mutations in the CDR2H and specific amino acid motifs in the CDR3H.