To analyze immunoregulatory abnormalities in patients with systemic lupus erythematosus (SLE) by assessing the expression of messenger RNA (mRNA) for types 1 and 2 recombination activating genes (RAG) in the peripheral blood of patients with active SLE.

We examined B cell populations and also individual B cells from patients with SLE for the expression of RAG mRNA.

Analysis of bulk mRNA indicated that RAG1 and RAG2 mRNA were found routinely in peripheral B cells of patients with active SLE, but not in healthy subjects. When assessed on a single‐cell basis, there was a 3‐fold increase in the frequency of RAG1‐ and RAG2‐expressing B cells in SLE patients compared with healthy subjects. Notably, B cells expressing both RAG1 and RAG2 mRNA expressed only IgD mRNA, but not IgG mRNA. Fifty percent of RAG‐expressing B cells also expressed VpreB mRNA, whereas all expressed CD154 mRNA. Phenotypic analysis indicated that RAG‐expressing B cells were activated, mature B cells.

These results indicate that RAG expression is up‐regulated in peripheral IgD+ and VpreB+ B cells of patients with active SLE. These cells may contribute to the immunoregulatory abnormalities in patients with SLE.