Bacteria-specific lymphocyte proliferation in peripheral blood in reactive arthritis and related diseases.

The cellular immune response seems to be important for the pathogenesis of reactive arthritis (ReA) and a bacteria-specific lymphocyte proliferation (LP) is often found in synovial fluid (SF) of ReA patients. However, the role of the bacteria-specific LP in peripheral blood (PB) is less well defined. In this study, we investigated 215 paired samples of SF and PB from patients with ReA (n = 65), undifferentiated oligoarthritis (n = 133) and undifferentiated spondylarthropathy (n = 17) to analyse the LP in PB and SF in relation to time. In 24 out of 87 patients (27.6%) with a bacteria-specific LP in synovial fluid, a positive LP to the same bacterium was also found in PB. While a positive LP in SF was found most frequently in the first week of the arthritis, a positive LP in PB was detected in 45% of patients when investigated between weeks 2 and 4 after the onset of arthritis, but was rarely found very early and late in the course of the arthritis. The time point seems to be crucial for the investigation of an LP in PB in patients with ReA.