Systemic lupus erythematosus (SLE) is characterized by the over production of high affinity autoantibodies against nuclear antigens. The disease associated autoantibodies play important roles in SLE pathogenesis, disease progression, and tissue/organ destruction. To gain insight into the mechanisms responsible for autoantibody generation in SLE, we performed single cell PCR analysis to study the functional antibody repertoires in three active SLE patients. Our initial analyses of 193 IgH genes derived from SLE plasma cells and naove B cells revealed many features of autoantibodies, such as long CDR3 regions with multiple positively charged Arg residues. Strikingly, both the IgH and IgL repertoires in the three active SLE patients showed signs of excessive rather than inefficient receptor editing, with elevated usages of downstream J:5 and J;3 genes in the IgL genes of some patients and significantly elevated frequencies of VH replacement products in the IgH genes in all three patients. Normally, receptor editing is aimed to delete Ig genes encoding self reactive antibodies. However, excessive receptor editing might have undesired consequences. Excessive editing of the IgL genes could exhaust the IgL repertoire with increased usage of the downstream J;3 gene. Such Ig;genes can not be changed by additional recombination. Excessive VH replacement will generate more IgH genes with long CDR3 enriched with charged amino acids, which might directly encode autoantibodies. Indeed, the identified VH replacement footprints preferentially encode charged amino acids within the CDR3 regions. Our initial test of 5 recombinant antibodies derived from VH replacement products showed that 3 of them strongly reacted with nuclear or peri-nuclear antigens. Based on these observations, we hypothesize that excessive receptor editing of IgH and IgL genes occurs in active SLE patients and contributes to the generation of high affinity autoantibodies against nuclear antigens. To test this hypothesis, (1) we will focus on a uniform population of newly diagnosed adult African-American female active SLE patients and perform single cell PCR and real time LM-PCR analyses to determine if excessive receptor editing occurs in these patients in comparison with age, gender and ethnic matched controls. We will perform follow-up studies to determine if excessive receptor editing correlates with disease activities in the same patients. (2) We will express recombinant antibodies using Ig genes derived from the plasma cells and naove B cells of SLE patients and normal controls to determine if accumulated VH replacement products in SLE plasma cells encode high affinity autoantibodies against nuclear antigens. Understanding the mechanism responsible for the generation of high affinity autoantibodies in SLE is timely important, which will allow us to design specific treatments to prevent or reduce autoantibody generation in SLE patients.