CXCR5 and lymphopenia: The absolute number of cTFH and all their subsets reflected the absolute number of CD4 T cells and was significantly lower in the ALPS-FAS patients with CD4 lymphopenia compared to ALPS-FAS patients without CD4 lymphopenia [cTFH (CXCR5+PD-1+: median 18.2 cells/μL (IQR: 12.8–35) vs. 57 cells/μL (IQR: 43.6–83.5), p = 0.003)], highly activated [TFH (CXCR5+PD-1high: median 10.7 cells/μL (IQR: 5.2–18.1) vs. 28.4 cells/μL (IQR: 18.1–40.4), p = 0.007)]), and [CD4+CXCR5+CCR7lowPD-1high: median 1.8 cells/μL (IQR: 1.5–2.5) vs. 3.7 cells/μL (IQR: 2–7), p = 0.03), respectively].