We have observed a higher percentage of CD4+CXCR5+PD-1+ cells in peripheral blood from SLE patients and CD4+CXCR5hiPD-1hiBcl-6+ frequency was positively correlated with SLEDAI, negatively correlated with ESR and C4 (unpublished data), which is consistent with the results of other studies20, 21, 22, indicating a critical role of Tfh cells in SLE. Here, C4A is linked to systemic lupus erythematosus.