To investigate the potential role of circulating TFH cells in children during the acute HSP, the frequencies of circulating CXCR5+CD4+TFH cells, ICOS+CXCR5+CD4+TFH cells, and PD-1+CXCR5+CD4+TFH cells were analyzed by flow cytometry (Figure 2). The gene discussed is PDCD1; the disease is hereditary spastic paraplegia.