TNF-alpha inhibition therapy affects the systemic immune response in rheumatoid arthritis by influencing T cell subtypes (Th1, Th2, Treg), but its effect on the intracellular signal transduction in T cells remains largely unexplored. Here we studied the activation of Th1-associated signalling molecule STAT4 and Th2-associated STAT6 in CD4+ T cells.
Eight rheumatoid arthritis patients were studied before and after 12 weeks of adalimumab therapy and compared to 8 healthy individuals. Peripheral blood mononuclear cells (PBMC) were analysed flow cytometrically either directly after isolation or after 24 hours of anti-CD3/anti-CD28 stimulation, to determine spontaneous and IL-4/IL-12-induced STAT4 and STAT6 phosphorylation in CD4+ T cells. Cytokine production by stimulated PBMC was measured in the supernatant using a cytometric bead array. Non-parametric statistical tests were applied.
After adalimumab therapy, phospho-STAT6 increased, both in freshly isolated and anti-CD3/anti-CD28-stimulated CD4+ T cells. The STAT6 response to brief IL-4 stimulation did not change. In healthy individuals and adalimumab-treated patients, anti-CD3/anti-CD28 induced the phosphorylation of STAT4, but not in untreated patients. IFN-gamma production in untreated patients was significantly lower than in healthy individuals or adalimumab-treated patients. In contrast, the production of IL-4, IL-6 and IL-12 was not influenced.
Adalimumab therapy increases Th2-associated STAT6 phosphorylation and restores the activation-induced STAT4 phosphorylation to the levels in healthy individuals. This advocates against a pro-inflammatory effect of Th1-associated STAT4 and might provide an explanation for the influence of TNF inhibition therapy on the systemic T cell response in rheumatoid arthritis.