BCR and systemic lupus erythematosus: There are studies reporting increased BCR signaling measured by Ca2+ release and downstream tyrosine phosphorylation related to a lack of negative regulation, such as by low-affinity immunoglobulin gamma Fc receptor II-b (FcγRIIb), phosphatase and tensin homolog (PTEN), or Lck/Yes novel tyrosine kinase (Lyn), in B cells from SLE patients (31–37).