Distinct effects of methotrexate and etanercept on the B cell compartment in patients with juvenile idiopathic arthritis

Abstract

Objective: B cells have been shown to play an important role in the pathogenesis of rheumatoid arthritis and juvenile idiopathic arthritis (JIA). Current treatments include the disease-modifying antirheumatic drugs methotrexate (MTX) and tumor necrosis factor α inhibition with etanercept. This study was undertaken to determine how these drugs influence the B cell compartment in patients with JIA.

Methods: B cell subpopulations and follicular helper T (Tfh) cells in the peripheral blood of JIA patients were investigated by multicolor flow cytometry. Serum immunoglobulin and BAFF levels were determined by enzyme-linked immunosorbent assay.

Results: There was a significant decrease in transitional B cells and significantly lower serum immunoglobulin levels in patients receiving MTX than in untreated patients and those receiving etanercept. In contrast, etanercept treatment had no effect on most of the B cell subpopulations, but resulted in significantly lower BAFF levels and increased numbers of Tfh cells. Thus, our findings indicate an unexpected and previously unknown direct effect of low-dose MTX on B cells, whereas etanercept had a more indirect influence.

Conclusion: Our results contribute to a better understanding of the potency of MTX in autoantibody-mediated autoimmune disease and present a possible mechanism of prevention of the development of drug-induced antibodies to biologic agents. The finding that MTX and etanercept affect the B cell compartment differently supports the notion that combination therapy with etanercept and MTX is more effective than monotherapy.

Figure 1

Effect of methotrexate (MTX) treatment on transitional and naive B cell numbers in patients with juvenile idiopathic arthritis (JIA) who were not treated (w/o) or were treated with nonsteroidal antiinflammatory drugs (NSAIDs), MTX, etanercept (Eta), or a combination of etanercept and MTX. A, Absolute B cell count per microliter. B and C, Percentage (left) and absolute number (right) of transitional B cells. D, Percentage (left) and absolute number (right) of mature naive B cells. Symbols represent individual patients; horizontal lines and error bars show the mean ± SEM. ∗ = P < 0.05; ∗∗ = P < 0.01; ∗∗∗ = P < 0.001.

Figure 2

Lower percentages of memory B cells, but no change in absolute memory B cell counts, in patients with JIA treated with etanercept. A, Percentage (left) and absolute number (right) of IgM+ (unswitched) memory B cells in patients with JIA receiving the indicated treatments. B, Percentage (left) and absolute number (right) of IgG+ (switched) memory B cells in patients with JIA receiving the indicated treatments. C, Ratio of IgM to IgG memory B cells in patients with JIA receiving the indicated treatments. Symbols represent individual patients; horizontal lines and error bars show the mean ± SEM. ∗ = P < 0.05; ∗∗ = P < 0.01; ∗∗∗ = P < 0.001. See Figure 1 for definitions.

Figure 3

Indirect effect of etanercept on the B cell compartment in patients with JIA. A, Decreased serum BAFF levels in etanercept-treated patients with JIA. B and C, Percentage (left) and absolute number (right) of follicular helper T (Tfh) cells in patients with JIA receiving the indicated treatments. Anti–tumor necrosis factor α treatment caused an increase in Tfh cells (CD4+CxRC5+PD-1+). Symbols represent individual patients; horizontal lines show the mean ± SEM. ∗ = P < 0.05; ∗∗ = P < 0.01. See Figure 1 for other definitions.

Figure 4

Decreased serum immunoglobulin levels in patients with JIA treated with MTX. A, IgM levels, B, IgG levels, and C, IgA levels in patients with JIA receiving the indicated treatments. Symbols represent individual patients; horizontal lines show the mean ± SEM. ∗ = P < 0.05; ∗∗ = P < 0.01; ∗∗∗ = P < 0.001. See Figure 1 for definitions.

Figure 5

Effect of MTX on transitional B cells and immunoglobulin levels in the subgroup of patients with oligoarticular JIA. The effect of MTX was similar to that found when all subgroups of JIA patients were included in the analysis. A, Percentage (left) and absolute number (right) of transitional B cells in untreated patients and patients treated with MTX. B, Percentage (left) and absolute number (right) of mature naive B cells in untreated patients and patients treated with MTX. C, Serum Ig levels in untreated patients and patients treated with MTX. Symbols represent individual patients; horizontal lines show the mean ± SEM. ∗ = P < 0.05; ∗∗ = P < 0.01. See Figure 1 for definitions.