In vitro and in vivo expression of a nephritogenic Ig heavy chain determinant: Pathogenic autoreactivity requires permissive light chains

Lymphocyte antigen receptors are promising targets for immune intervention strategies in disorders marked by repertoire skewing or expansion of lympho cyte subsets. Appropriate application of immune receptor modulation is pred icated on understanding the role of a particular receptor in pathogenesis a nd disease regulation. The V-H(B/W16) gene; restricted to mice carrying the j haplotype for the J558 family, is overexpressed by murine lupus anti-DNA Ig, This gene is also expressed recurrently among nephritogenic anti-DNA I g recovered from several autoimmune strains, suggesting that cells expressi ng this pathogenic receptor are positively selected during disease progress ion. To explore the extent and mechanisms by which Ig H chains expressing t his gene contribute to autoimmunity, an Ig H chain gene was engineered for in vitto and in vivo recombination studies. Site-directed mutagenesis gener ated unique restriction sites to link PCR-amplified V region (VDJ) cDNA to previously isolated genomic fragments containing Ig regulatory and signal s equences. The new 3 kb VDJ gene was then ligated to a 9 kb fragment encodin g the IgM constant region. Transfection of H chain loss variant myeloma wit h the complete 12kb construct, termed 238H-C mu, resulted in secretion of i ntact Ig pairing 238H-C mu with a lambda L chain; however, transfectant Ig lacked autoreactivity and pathogenicity. Introduction of the 23 8H-C mu H c hain as a transgene onto the non-autoimmune C57BL/6 background resulted in abundant B cell surface expression of 238H-C mu, however, four transgenic I g recovered by fusion of LPS-stimulated splenocytes and formed by combinati on of 238H-C mu with endogenous kappa chains do not bind DNA or laminin. Th ese results indicate that the antigen binding sites encoded by this disease -associated gene and/or H chain must associate with permissive L chains to specify autoimmunity. The 238H-Cu transgenic model should prove useful in d issecting the in vivo fate of 238H-C mu -L combinations that produce pathog enic autoreactive receptors and in evaluating receptor-targeted interventio ns.