AUTOANTIBODIES IN MICE LACKING TERMINAL DEOXYNUCLEOTIDYL TRANSFERASE - EVIDENCE FOR A ROLE OF N REGION ADDITION IN THE POLYREACTIVITY AND IN THE AFFINITIES OF ANTI-DNA ANTIBODIES

The generation of terminal deoxynucleotidyl transferase knockout mice (TdT(0)) has demonstrated that TdT is the only major activity involved in N region addition. This enzyme generates diversity by adding rando m nucleotides at the V-D-J junctions and by disrupting the formation o f repetitive ''homology-directed'' junctions. Several studies have dem onstrated that the Ig heavy chain third complementarity-determining re gion (H-CDR3) and the N regions play a critical role: 1) in distinguis hing between polyreactive and monospecific combining sites in natural and Ag-induced Abs; and 2) in the specificity and polyreactivity of na tural autoantibodies (autoAbs) and in particular of anti-DNA Abs. To e xamine the impact of the lack of TdT on the natural autoAb repertoire in adult mice, we have stimulated TdT(0) and TdT(+) littermates with L PS. Serum studies demonstrate that TdT is not critical for the generat ion of B cells expressing autoAbs including anti-DNA Abs and rheumatoi d factors. However, the generation of a large collection of hybridomas indicates that the frequencies of these cells are reduced in TdT(0) m ice mainly due to a lower incidence of polyreactivity; also, the lack of N region diversity seems to negatively affect the affinity of anti- DNA Abs. The physiologic relevance of these data is discussed.