BTK and myeloid sarcoma: To address whether BTK is differentially regulated in B cells during the pathogenesis of MS, we compared BTK protein expression and phosphorylation in ex vivo peripheral blood B cells from the healthy control (HC), CIS, RRMS, SPMS, and PPMS subgroups (Figure 1, A–C, and Supplemental Table 1; supplemental material available online with this article; https://doi.org/10.1172/jci.insight.160909DS1).