No significant differences were identified in the proportion of cTfh or highly activated cTfh in ALPS-FAS patient with or without CD4 lymphopenia (Figures 7A,B); however, a particular subpopulation of cTfh, CXCR5+CD4+CCR7lowPD-1high, which has been highly correlated with autoantibody production in rheumatoid arthritis and SLE (11), was largely expanded in ALPS-FAS CD4 lymphopenic patients compared to ALPS-FAS patients without CD4 lymphopenia [median 20.1% (IQR: 7.73–27) vs. 7.94% (IQR: 5.61–9.93), p = 0.025)] (Figures 7C,D). Here, CXCR5 is linked to lymphopenia.