Differential expression patterns of recombination-activating genes in individual mature B cells in juvenile idiopathic arthritis

Background: Re-expression of the recombination-activating genes (RAG) in peripheral B cells may be relevant in the development of autoreactive antibodies in autoimmune diseases. The presence of antinuclear antibodies (ANA) as a hallmark of oligoarticular juvenile idiopathic arthritis (o-JIA, early-onset type) indicates a breakdown in immunological tolerance. Aim: To examine the expression of RAG genes in peripheral blood mature B lymphocytes in patients with o-JIA. Methods: 777 memory B cells from peripheral blood, CD19+ CD27+ CD5+ or CD19+ CD27+ CD5−, isolated from three ANA+ children with o-JIA and three healthy age-matched children, were examined for the expression of RAG1 and RAG2 mRNA. mRNA transcripts of activation-induced cytidine deaminase and immunoglobulin G were searched to further determine their developmental stage. Results: mRNA was present for any of the two RAG genes in the B cells of children with JIA and controls. However, the predominance of RAG1 or RAG2 was different. A significantly decreased frequency of RAG2-expressing memory B cells in both CD5+ and CD5− populations was noted in children with JIA (p