PTPN22 and systemic lupus erythematosus: Interestingly, proteins involved in the positive (Blk, BANK1) and negative (PTPN22/PEP, Csk, FcγRIIA, FcγRIIB, FcγRIIIA, FcγRIIIB, SOCS1) signaling pathways in B cells have all been linked to SLE via genome-wide association studies (GWAS) and this highlights the importance of regulating these signaling cascades to avoid disease onset or progression (138–143).