Absence of circulating memory B cells and gut plasma cells and accumulation of newly generated B cells in PB of ICF patients. PBMCs from 4 ICF patients (P1 to P4) and HDs were analyzed by flow cytometry (panels A-C). In panels A to C, representative dot plots and histograms are shown for 1 adult and 1 child HD of 5 adults and 5 children. (A) Four-color flow cytometry analysis of anti-CD19, anti-CD27, anti-δ, and anti-μ staining. Expression of CD19 and CD27 on PBLs and of surface μ and δ within the CD19⁺ gate are represented in the top and bottom subpanels, respectively. (B) PBMCs from P1, P3, P4, and HDs were stained with anti-CD19, anti-CD27, and anti-CD21 or anti-CD23 and analyzed within the CD19⁺CD27^- gate. (C) PBMCs from P1, P4, and HDs were stained with anti-CD19, anti-CD38, anti-δ, and anti-CD10 and were then analyzed within the CD19⁺ gate. Numbers in quadrants (A,C) and brackets (B) indicate percentage of cells within the corresponding gate. (D) Jejunal sections from a healthy child and P4 were paraffin embedded and formalin fixed. IgA staining is shown in red, hematoxylin counterstaining in blue; magnification, × 250. IgA⁺ plasma cells (PCs) are indicated by yellow arrows; secretory IgA is indicated by a white arrow. Results are representative of P2, P3, P4, and 10 age-matched controls.