Expression of kappa-opioid receptor mRNA in human peripheral blood lymphocytes and the relationship between its expression and the inflammatory changes in rheumatoid arthritis

The expression of the kappa-opioid receptor on human peripheral blood cells (in rheumatoid arthritis cases and normal volunteers) was examined using r everse transcriptase polymerase chain reaction (RT-PCR), and the relationsh ip between its expression and the inflammatory activity or chronic pain in patients with rheumatoid arthritis (RA) was determined. RT-PCR was performe d on the peripheral blood cells obtained from 37 patients with RA and 13 he althy volunteers. kappa-Opioid receptor mRNA expression was exhibited on th e blood cells of 37% of RA patients (14/ 37) and 54% of healthy volunteers (7/13), and the levels of expression were lower in the RA patients than in the healthy volunteers. Regarding the relationship between the expression o f kappa-opioid receptor mRNA and the symptoms in RA patients, it was noted that the expression of the receptor mRNA was significantly decreased in RA patients in whom erythrocyte sedimentation rate (ESR), Lansbury index, and visual analogue pain scores were high. The kappa-opioid receptor mRNA was e xpressed on four cell types, namely, T and B cells, macrophages, and natura l killer (NK) cells in RA patients; however, it was expressed only on the T and B cells and macrophages (and not on NK cells) in the healthy volunteer s. Our findings suggest that the levels of expression of kappa-opioid recep tor mRNA were decreased in RA patients in comparison with those in healthy volunteers; and that they were significantly related to the inflammatory ac tivity or chronic pain in the RA patients. The higher the mRNA expression l evel, the less severe the inflammatory changes of RA. The kappa-opioid rece ptor may thus play a role in the modulation of nociception and anti-inflamm atory changes in chronic inflammatory disorders.