Expression of the multidrug resistance glycoprotein 170 in the peripheral blood lymphocytes of rheumatoid arthritis patients. The percentage of lymphocytes expressing glycoprotein 170 is increased in patients treated with prednisolone.

The objective was to evaluate the expression of the multidrug resistance P-glycoprotein (P-gp) in peripheral blood lymphocytes (PBL) of patients with rheumatoid arthritis (RA). PBL from 68 RA patients and 44 controls were evaluated. RA patients had a mean disease duration of 10.7 yr, with a mean number of past resistances to DMARDs of 0.82, and were treated with NSAIDs (n = 34), DMARDs (n = 25) and prednisolone (n = 40). Fluorescence flow cytometry was used to assess P-gp membrane expression on PBL. In the RA group, the percentage of PBL expressing P-gp was higher in patients treated with prednisolone than in other patients [mean +/- S.D.: 10.7 +/- 15.8% vs 3.3 +/- 7.6%, P < 0.03, Student] and was not related to other therapies, age, sex, RA duration, number of past resistances to DMARDs, activity, ESR, CRP. The percentage of PBL expressing P-gp did not differ in RA and control groups, but was higher in the prednisolone-treated RA patients than in controls. Prednisolone could induce a rise in the percentage of PBL expressing P-gp. On the contrary, patients with a high percentage of PBL expressing P-gp could be more resistant to DMARDs and need prednisolone earlier. Further studies are needed to address this question and to evaluate the potential implication of P-gp in drug resistance in RA.