We next investigated whether there was an intrinsic IL-10 defect in patient B cells using the CD40–CD40L interaction which is key for B cell development and induces IL-10 in B cells (80) Contrary to Kalampokis et al., who reported a reduction in Breg IL-10 in JDM patients (81), we did not observe a difference in JDM patients pre-treatment and controls with the CD40L stimulus, indicating that patient B cells can produce IL-10 with CD40 activation. Here, CD40 is linked to juvenile dermatomyositis.