LCK and systemic lupus erythematosus: To study whether SLE‐enriched exosomal ECP plays an important role in the pathogenesis of SLE, we generated and characterized Lck‐ECP–transgenic mice (Supplementary Figures 3A and B, available on the Arthritis & Rheumatology website at http://onlinelibrary.wiley.com/doi/10.1002/art.41920/abstract).