BCR and systemic lupus erythematosus: Blk phosphorylates the Ig α‐ and β‐subunits of the BCR and is known to bind the phosphatidylinositol lipase C‐γ230, forming a complex with the B cell adaptor protein ankyrin repeats (encoded by the BANK1 gene and, interestingly, also a susceptibility locus for SLE) during BCR signaling 38.