Objectives To examine the expression of the multidrug resistance P-glycoprotein (P-gp 170) in patients with rheumatoid arthritis (RA). P-gp 170 is a pump molecule which decreases intracellular drug concentrations by increasing drug efflux from cells.

Methods Peripheral blood samples were obtained from 10 patients with active RA, and 8 normal subjects. The patients were treated with NSAIDs. Previous therapy with DMARDs was ineffective in 7 patients. 3 patients were not treated with DMARDs. Fluorescent flow cytometry on FACScan (Becfon Dichinson) was used to assess the expression of P-gp 170, with monoclonal antibodies (UIC2 PE, Immunotech).

Results The expression of P-gp on peripheral blood lymphocytes was elevated compared with control (29,6 ± 9,4% vs 1,6 ± 0,4%, P = 0,03). We did not observe any association between glycoprotein P expression and age, sex, disease activity, duration and stage of RA. The expression of P-gp 170 correlated with expression of antigens CD8 (r = 0,85) and CD71 (r = 0,83).

Conclusion The patient with RA showed increased expression of P-gp 170 as compared to the control. Further studies are needed to evaluate the potential implication of P-gp in drug resistance in RA.