CD19 and pulmonary fibrosis: When ibrutinib, a BTK inhibitor, was administrated in the topo I-induced SSc model mice generated by four times immunization with topo I, frequencies of topo I-APC+ topo I-PE+ CD19+ cells were significantly reduced, and skin and lung fibrosis was also attenuated compared to the model mice without the BTK inhibitor (p<0.05, respectively; Figure 7A and B).