BTK and autoimmune disease: However, when BTK is overexpressed by the abnormal signal transmission of BCR in B cells, the BCR signaling system undergoes excessive phosphorylation gradually and causes abnormal B-cell proliferation and pathological autoantibody formation, resulting in systemic erythematous lupus, cancers, rheumatoid arthritis, autoimmune diseases, B-cell malignancies, and inflammatory diseases [4,5].