Weller S, Conde C, Knapp A M, Levallois H, Gilfillan S, Pasquali J L, Martin T
Laboratory of Immunopathology, Central Hospital, University Hospitals of Strasbourg, France.
J Immunol. 1997 Oct 15;159(8):3890-8.
The generation of terminal deoxynucleotidyl transferase knockout mice (TdT0) has demonstrated that TdT is the only major activity involved in N region addition. This enzyme generates diversity by adding random nucleotides at the V-D-J junctions and by disrupting the formation of repetitive "homology-directed" junctions. Several studies have demonstrated that the Ig heavy chain third complementarity-determining region (H-CDR3) and the N region play a critical role: 1) in distinguishing between polyreactive and monospecific combining sites in natural and Ag-induced Abs; and 2) in the specificity and polyreactivity of natural autoantibodies (autoAbs) and in particular of anti-DNA Abs. To examine the impact of the lack of TdT on the natural autoAb repertoire in adult mice, we have stimulated TdT0 and TdT+ littermates with LPS. Serum studies demonstrate that TdT is not critical for the generation of B cells expressing autoAbs including anti-DNA Abs and rheumatoid factors. However, the generation of a large collection of hybridomas indicates that the frequencies of these cells are reduced in TdT0 mice 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.
末端脱氧核苷酸转移酶基因敲除小鼠（TdT0）的产生表明，TdT是参与N区添加的唯一主要活性酶。该酶通过在V-D-J连接点添加随机核苷酸以及破坏重复性“同源性定向”连接点的形成来产生多样性。多项研究表明，免疫球蛋白重链第三互补决定区（H-CDR3）和N区发挥着关键作用：1）在区分天然抗体和抗原诱导抗体中的多反应性和单特异性结合位点方面；2）在天然自身抗体（自身抗体）尤其是抗DNA抗体的特异性和多反应性方面。为了研究缺乏TdT对成年小鼠天然自身抗体库的影响，我们用脂多糖刺激了TdT0和TdT+同窝小鼠。血清研究表明，TdT对于表达包括抗DNA抗体和类风湿因子在内的自身抗体的B细胞的产生并非至关重要。然而，大量杂交瘤的产生表明，这些细胞在TdT0小鼠中的频率降低，主要是由于多反应性发生率较低；此外，缺乏N区多样性似乎对抗DNA抗体的亲和力产生负面影响。本文讨论了这些数据的生理相关性。
