Infrequency of detection of particle‐associated MSRV/HERV‐W RNA in the synovial fluid of patients with rheumatoid arthritis

Objectives. To determine whether the recently identified multiple sclerosis‐associated retrovirus, MSRV, is detectable in the serum and synovial fluid of patients with rheumatoid arthritis (RA). Methods. A reverse transcription–polymerase chain reaction (RT‐PCR) assay was used to seek evidence of particle‐associated MSRV/HERV‐W RNA in the plasma and synovial fluid of patients with RA and controls. Stringent precautions were taken to avoid detection of contaminating human genomic DNA and cellular RNA sequences. Results. Thirty‐seven plasma samples were tested (20 from RA patients and 17 from controls) but none had detectable MSRV/HERV‐W RNA. Synovial fluid samples were available from nine patients with RA and 10 controls. Particle‐associated MSRV/HERV‐W RNA was reproducibly detected in two of nine synovial fluid samples from RA patients and in one control sample. The identity of RT‐PCR products was confirmed by sequencing. Conclusion. MSRV/HERV‐W RNA sequences are detectable in the synovial fluid of a small proportion of RA patients, but this phenomenon may not be specific to RA.