IL21 and systemic lupus erythematosus: Moreover, TYK2 polymorphism is closely linked with SLE.282 CXCR4, a vital chemokine receptor with multiple immune functions, is significantly upregulated in patients with SLE.283,284 CXCR4 endocytosis is mediated through IL-21 and B-cell receptor interactions, which are likely dependent on the JAK/STAT signaling pathway.285 Furthermore, CXCR4 undergoes tyrosine phosphorylation by JAK2 and JAK3.286 These data indicate that the activated JAK/STAT pathway is tightly associated with an abnormal increase in CXCR4 in patients with SLE.