Anti-DNA IgA autoantibodies play an important immunopathologic role in SLE patients. To analyze the cellular origin and the V(H) and V(L) structure of anti-DNA IgA autoantibodies, we generated five IgA1 mAbs to DNA using B lymphocytes from three SLE patients. Two mAbs bound to ssDNA only and one to both ssDNA and dsDNA (monoreactive antibodies). The remaining two mAbs bound to DNA (one to ssDNA and the other to both ssDNA and dsDNA) and to other self and foreign Ag (polyreactive antibodies). The IgA mAb relative avidity for DNA ranged from 7.5 x 10-8 to 8.0 x 10-10 g/μl. The anti-DNA IgA mAb used V(H) segments of the V(H)I (VI-3b), V(H)II (V(H)2-MC2), V(H)III (WHG16G and V(H)26c), and V(H)IV (V71-2) families in conjunction with VκI, VκIIIb, or VλI segments. All IgA mAb V(H) segments were juxtaposed with J(H)4b segments. The heavy chain CDR3 sequences were divergent in composition and length. When compared with those of the closest reported germ line genes, the IgA mAb V(H) and V(L) gene sequences displayed a number of differences. That these differences represented somatic point mutations was formally proved in both the monoreactive IgA mAb 412.67.F1.3 and the polyreactive IgA mAb 412.66.F1 V(H) segments by differential PCR amplification and cloning and sequencing of genomic DNA from the mAb-producing cell lines and autologous polymorphonuclear cells. The sequences of the germ line genes that putatively gave rise to the mAb 412.67.F1.3 and mAb 412.66.F1 V(H) segments were identical with those of the WHG16G and V(H)26c genes, respectively. In not only the monoreactive mAb 412.67.F1.3 but also the polyreactive mAb 412.66.F1 and mAb 448.9G.F1 V(H) segments, the higher concentration of replacement (R) mutations and the higher R:S (silent) mutation ratios in the complementarity- determining region (∞; 19:0) than in the framework region (1.0) (p = 0.00001, χ2 test) were highly consistent with selection by Ag. In the five IgA mAb V(H) and V(L) segments, the putative and verified somatic point mutations yielded 68 amino acid replacements, of which 38 were nonconserved. Twenty of these yielded positively charged or polar residues that play a major role in DNA binding, including seven Arg, five Lys, three Tyr, two Gln, two His, and a Thr. The conserved amino acid changes included seven Asn. These findings suggest that anti-DNA IgA autoantibodies use a broad selection of V(H) and V(L) genes and enhance their fit for Ag by undergoing somatic hypermutation and Ag selection. Such a hypermutation and Ag selection process would apply to originally polyreactive, in addition to monoreactive natural DNA binding IgA autoantibodies.
|Original language||English (US)|
|Number of pages||15|
|Journal||Journal of Immunology|
|State||Published - Jan 1 1994|
ASJC Scopus subject areas
- Immunology and Allergy