ANTI-DNA AND ANTIPLATETLET SPECIFICITIES OF SLE-DERIVED AUTOANTIBODIES - EVIDENCE FOR CDR2(H) MUTATIONS AND CDR3(H) MOTIFS

Although polyreactivity appears to be a characteristic feature of natu ral autoantibodies, polyreactive anti-DNA autoantibodies can be derive d both from patients with autoimmune disease and from normal individua ls. It is unclear whether these autoantibodies differ depending on the ir origin, but previous studies from our laboratory have suggested tha t polyreactive systemic lupus erythematosus (SLE)-derived platelet-bin ding anti-DNA autoantibodies have more restricted antigen reactivity a nd greater functional activity than normal-derived polyreactive autoan tibodies. The objective of the present study was to characterize the V -H and V-L region sequences of 10 human hybridoma anti-DNA autoantibod ies derived from peripheral blood lymphocytes of different origins [SL E, rheumatoid arthritis (RA), or normal] to determine whether there ar e structural differences between these autoantibodies. We show that al though some unmutated germline structures (V-H and V-L) are represente d, these are not restricted to anti-DNA autoantibodies from normal ind ividuals and that two normal-derived anti-DNA antibodies showed quite extensively mutated V-H genes. However, these mutations, unlike those found in the CDR2(H) of several of the SLE-derived antibodies, did not appear to be antigen-selected. Three different amino acid motifs, put atively involved in antigen binding specificity, were observed in the CDR3(H) segments of some of the autoantibodies. One was the previously described YYGSG motif, which was found in a normal-derived anti-DNA a utoantibody, while two new potential motifs were observed only in SLE- derived platelet-binding anti-DNA autoantibodies. These data suggest t hat antigenic and functional differences between SLE-derived and norma l-derived platelet-binding anti-DNA autoantibodies may be due to antig en-selected mutations in the CDR2(H) and specific amino acid motifs in the CDR3(H).