PDCD1 and systemic lupus erythematosus: Furthermore, due to too few cells after stimulation, the failure to perform further subset analysis of cTfh1, cTfh2 and cTfh17 in MRL/lpr mice based on the expression of PD1 and ICOS is also a limitation of this study, and modified animal experiments should be performed to explore the role of Tfh cells and their subsets in lupus mice in the future.