The Immunosuppressive Effect of Methotrexate in Active Rheumatoid Arthritis Patients vs. its Stimulatory Effect in Nonactive Patients, as Indicated by Cytometric Measurements of CD4 + T Cell Subpopulations

This cytometric study assesses the effects of methotrexate (MTX) on the expanded CD4+ lymphocyte population in active and nonactive rheumatoid arthritis (RA) patients. In the active patients, MTX was found to reduce the predominant CD4+ CD28+ subpopulation (by 30%), and the minor subpopulation of CD4+ CD28- (by 34%). The incidence of CD25 phenotype was downregulated by 15%. These reductions can be attributed to immunosuppression through apoptosis, which was demonstrated by MTX-induced fluorescein diacetate (FDA) hyperpolarization (an established indicator of early apoptosis). In contrast, in nonactive RA patients, the major CD4+ CD28+ subpopulation of small lymphocytes appeared to be activated by MTX, subsequently transforming into a major hyperblast population, whereas the minor CD4+ CD28- subpopulation was not affected by MTX treatment. The activation by MTX in this group of patients is evidenced by MTX-induced FDA depolarization (an indicator of early activation). Thus, MTX immunosuppressive effect on CD4+ subsets was found in active patients, whereas immunostimulation by MTX was shown in nonactive patients. The found discriminative effect of MTX may suggest a higher effectiveness of low-dose MTX therapy in active RA patients.