A proportion of patients with rheumatoid arthritis (RA) fail to respond adequately to corticosteroid (CS) therapy. Using an in vitro CS sensitivity bioassay, we have subdivided RA patients into steroid-sensitive (SS) and -resistant (SR) subgroups and this correlates with clinical responses to CS therapy. CSs exert their effects via the CS receptor (CR), which exists as two main isoforms, CRalpha and CRbeta. CRbeta can function as a negative inhibitor of CRalpha. We have hypothesized that steroid resistance in RA patients is due in part to a relative over-expression of the CRbeta.
Peripheral blood mononuclear cells (PBMCs) were isolated from SS and SR RA patients. CRalpha and CRbeta mRNA expression was determined by quantitative real time polymerase chain reaction (qRT-PCR). The ratio of CRbeta/CRalpha mRNA expression was determined. CRalpha and CRbeta protein expression by PBMCs was analysed by flow cytometry.
qRT-PCR analysis showed a trend towards higher expression of both CRbeta and basal CRbeta/CRalpha ratio in SR RA patients. Stimulation of PBMCs in vitro with concanavalin-A induced a significantly higher CRbeta mRNA expression, and CRbeta/CRalpha ratio in SR RA patients compared with SS patients, which was not inhibited by hydrocortisone. Flow cytometry showed that the percentage of PBMCs staining for CRbeta protein was significantly lower in the SS RA group (SS 43.3 +/- 14.8% vs SR 88.6 +/- 8.6%; P < 0.0010). The mean intensity of fluorescence CRbeta staining was higher in the SR RA patients (P < 0.001).
We show for the first time that CRbeta is over-expressed in SR RA patients and that hydrocortisone fails to inhibit concanavalin-A stimulated increase in CRbeta mRNA in SR RA patients. This mechanism may contribute in part to the CS hyporesponsiveness seen in some RA patients.