CXCL13 and common variable immunodeficiency: The association of higher CXCL13 with patients having high CD21low B cell or low switched memory B cell frequency and its weak correlation – although not statistically significant - with the frequency of CD21low B cells and switched memory B cells corroborate the suggestion for its use as a biomarker of complex phenotype in CVID (Figs. 8 and S10, supplementary material).