CD4 and systemic lupus erythematosus: Although we showed the potential roles of the circPTPN22/miR-4689/S1PR1 axis in modulating T-cell functions using Jurkat T cells as a model, which are well-known CD4+ T cells, its functions in various immune cell subpopulations need to be further explored in the future to provide more exact mechanisms to fine-tune the immune response during SLE treatment.