SYK and systemic lupus erythematosus: In SLE T cells the replacement of CD3ζ with the FcRγ, induces the binding of the spleen tyrosine kinase (Syk) with high affinity instead of ZAP-70, which results in a much stronger calcium influx into the T cell cytoplasm and which in turn leads to a decreased activation threshold of CD4+ T and B cells upon autoantigen recognition.