FCRL4 and common variable immunodeficiency: SOX5 transcription varied between peripheral blood B-cell subpopulations, showing the highest expression levels in circulating innate-like CD21low B cells and non-classical CD27− memory B cell populations, as we had previously seen in CD21low B cells of patients with CVID [16] and others in FCRL4+ tissue-like memory B cells of tonsils [15].