CXCR5 and hereditary spastic paraplegia: In this study, CD4+ CXCR5+ and CD4+ CXCR5+ ICOS+ Tfh cells were abnormally elevated in children with non-nephritis-type HSP, and were significantly associated with PGA-IgA, especially CD4+ CXCR5+ ICOS+-activated Tfh cells.