IRF4 and rheumatoid arthritis: As in the experiment with the original infliximab, there were no significant variations in the percentages of PU.1+, IRF4+ Th9 cells, under basal or stimulated conditions, in the healthy controls and the untreated or responding RA patients, but the addition of the biosimilar did not significantly increase the percentage of PU.1 and IRF4-expressing, IL-9-secreting CD4+ T cells or IL-9-secreting central and effector memory CD4+ T cells in the infliximab IR group, as was observed after the addition of branded infliximab (Figure 1, Figure 4 and Figure 5).