CD81 loss in blasts from ALL patient 3 disrupts CD19 membrane trafficking. (A) Reverse transcription polymerase chain reaction (RT-PCR) analysis of CD19 mRNA expression in ALL patient 3 and primary CLL⁺ control cells as well as PC-3 and LNCap prostate negative control cell lines. (B) Schematic representation of CD81-dependent CD19 cell surface transport via endoplasmic reticulum (ER) and Golgi compartments. (C) Flow cytometric analysis of CD81 membrane expression on blasts from ALL patient 3 and healthy donor CD19⁺ B cells. (D) CD19 western blot analysis using lysates from ALL patient 3 and control CLL cell lysates ± PNGaseF treatment of deglycosylation. (E) Lectin western blot analysis revealing global glycosylation patterns in cell lysates from ALL patient 3 and control CLL as well as healthy donor blood cell lysates. B-ALL, B-cell ALL; PE, phycoerythrin.