In a previous experiment, we found an increased prevalence of IFNγ-, IL-4-, IL-17-, IL-9-secreting CD4+ T cells in RA patients, although there was no significant association with therapeutic outcomes [25]; this unusual behaviour may be related to the heterogeneity and plasticity of IL-9-producing CD4+ T cells, which may also include regulatory cells [26]. This evidence concerns the gene IL4 and rheumatoid arthritis.