BCR and Alzheimer disease: The non‐receptor tyrosine kinase called spleen tyrosine kinase (SYK) is expressed in various cell types and is coupled with immune receptors such as the B‐cell receptor (BCR), T‐cell receptor (TCR), Toll‐like receptor 4 (TLR4), and triggering receptor expressed on myeloid cells‐2 (TREM2).[52, 53, 54] TREM2 is a well‐known receptor of fibrillary Aβ and is closely associated with AD.