Effect of genetic deficiency of terminal deoxynucleotidyl transferase on autoantibody production and renal disease in MRL/lpr mice.

Terminal deoxynucleotidyl transferase (TdT) places non-template-coded nucleotides (N additions) in the VH CDR3 of T cell receptors and immunoglobulins. Amino acids coded for by N additions are important in autoantibody binding of dsDNA in lupus. We hypothesized that a genetic lack of TdT would modulate disease in lupus-prone mice. To test this hypothesis, we derived TdT-deficient MRL/lpr mice. Serum levels of anti-dsDNA antibodies and anti-dsDNA producing splenocytes were significantly lower in the TdT(-) versus TdT(+) littermates. Albuminuria, glomerular IgG deposition, and pathologic renal disease were significantly reduced in the TdT(-) mice. Sequence analysis of anti-dsDNA hybridomas derived from TdT(-) mice revealed a lack of N additions, short VH CDR3 segments, yet the presence of VH CDR3 arginines. Thus, the genetic absence of TdT reduces autoantibody production and clinical disease in MRL/lpr mice, confirming the importance of N additions in the autoimmune response in these mice.