Decreased mRNA expression of two FOXP3 isoforms in peripheral blood mononuclear cells from patients with rheumatoid arthritis and systemic lupus erythematosus.

Both the number and functional capacity of T-regulatory (Treg) cells are known to be decreased in various autoimmune diseases. FOXP3, an essential transcription factor for Treg cells, has three isoforms in humans, wild, and exon 2- and exon 2-exon 7-lacking, although their role in autoimmunity is not clearly understood. Here, we investigated the messenger RNA (mRNA) expression of the major wild and exon-2 isoforms in peripheral mononuclear cells by quantitative PCR methods in 56 subjects, consisting of 23 rheumatoid arthritis (RA) and 25 systemic lupus erythematosus (SLE) patients, and 8 healthy controls (HCs). Although mRNA expression of the two isoforms did not directly correlate with clinical disease activity, relative expression of both was significantly lower in SLE and RA patients than in HCs. Furthermore, we found a significant statistical correlation between the two isoforms, suggesting that they are similarly regulated. Decreased expression of these isoforms in RA and SLE may reflect Treg cell abnormalities in these autoimmune diseases.