Molecular analysis of cross-reactive anti-myosin/anti-streptococcal mouse monoclonal antibodies.

Nucleotide sequences of VH- and VL-genes of anti-myosin/anti-streptococcal monoclonal antibodies (mAbs) were analyzed and compared with their highly detailed antigen binding reactivities. Antigen-specificities of the cross-reactive mAbs included myosin, streptococcal M-protein, actin, keratin, N-acetyl-beta-D-glucosamine, vimentin, DNA, tropomyosin, troponin, and laminin as previously described. After nucleotide sequence analysis, homology indicated that some of the V gene sequences aligned with antibodies recognizing gangliosides and blood group antigens glycophorin M and N. Therefore, mAb reactivity with gangliosides and glycophorin M and N was identified. The cross-reactive mAbs utilized a heterogeneous group of germline V-heavy genes comprised of nine J558-, four 7183- and two Q52-family VH-genes. Germline V-light genes utilized by the mAbs included six Vkappa4/5-, three Vkappa8-, two Vkappa10-, three Vkappa19- and one Vkappa23-family VL-genes. No preferential VH/VL-chains correlated with any of the 12 different antigen reactivities, even for mAbs with nearly identical cross-reactivities. However, we did find that the cross-reactive mAb germline genes within a V gene family shared more homology among themselves than with other germline genes within their V gene families, suggesting convergent mutation. Cross-reactive mAbs with the highest relative avidity for myosin were found in the VH7183 family which contained two cytotoxic mAbs. Antibodies with V gene sequences most homologous to those of our cross-reactive anti-myosin/anti-streptococcal mAbs had specificities for laminin, DNA, carbohydrates, or blood group antigens and were reported to cause autoimmune disease in mice.

Molecular analysis of V gene sequences encoding cytotoxic anti-streptococcal/anti-myosin monoclonal antibody 36.2.2 that recognizes the heart cell surface protein laminin.

Anti-streptococcal/anti-myosin mAb 36.2.2 is unique among the cross-reactive anti-streptococcal mAbs due to its cytotoxicity for rat heart cells and its ability to strongly label the surface of heart cells in indirect immunofluorescence assays. In this study, cytotoxic mAb 36.2.2 was found to react strongly with the extracellular matrix protein laminin in immunoblots and inhibition assays, while 11 other cross-reactive anti-streptococcal mAbs did not react with laminin and were not cytotoxic. Cytotoxicity appeared to correlate with the presence of laminin on the surface of cells. Heavy and light chain variable region genes encoding mAb 36.2.2 were highly homologous to other V genes encoding anti-carbohydrate and/or autoantibodies. VH, JH, and Jkappa segments of mAb 36.2.2 may be encoded by germline gene segments. The VH segment may be identical with an as yet unidentified VH7183 family germline sequence, and the 36.2.2 Vkappa region gene is encoded by a Vkappa8 family member.