BTK and idiopathic pulmonary arterial hypertension: As we found BTK overexpression in B cells from patients with IPAH, we focused on this group of patientsH for the evaluation of cTfh cells, which can be induced by BTK overexpression in B cells.18 Based on surface C–C chemokine receptor 6 (CCR6) and C–X–C motif chemokine receptor 3 (CXCR3) expression, different cTfh subsets can be discriminated with cytokine profile characteristics of Th1, Th2 and Th17 cells19 (figure 5A).