PDCD1 and systemic lupus erythematosus: To further explore phenotypic plasticity, we activated sorted Tfh cells from SLE-prone B6.Sle1yaa mice in vitro and observed a reduction in CXCR5 expression, while PD-1 expression was maintained (Figure 8I), suggesting a partial phenotypic shift toward a Tph-like phenotype after stimulation in vitro.