Binding of mannose-specific bacterial lectins stimulates FL receptors via V-region N-glycosylation. (A) Binding profile of bacterial lectins to FL-BCRs and the glycosylation-defective mutants expressed on TKO cells by FACS analyses. Empty-vector–transduced cells and BCR53⁺ cells served as controls. (B) Ca²⁺ mobilization of ERT2-SLP65⁺ TKO cells reconstituted with the indicated receptor variants upon stimulation with bacterial lectins or anti-BCR stimulation at the indicated concentrations in medium containing 1% FCS. (C) BCR surface expression on primary FL and HD PBMCs was acquired using anti-human CD19 and anti-human LC antibodies. Binding profile of Bc2L-A to CD19⁺- compared with CD19⁻-gated cells in FL sample from lymph node biopsy specimen or healthy donor control measured by FACS. (D) Ca²⁺-influx measurement of primary FL sample and healthy control PBMCs pregated on CD43⁻ cells upon addition of the indicated stimuli after 1-minute baseline measurement. Experiments were performed in medium containing 1.5 mM Ca²⁺. (E) Mean fluorescence intensity values of Bc2L-A binding in CD19⁺ referred to CD19⁻ cells revealed 2 FL subsets: binders and nonbinders (left). Statistical analysis of Ca²⁺-influx measurements of primary samples displayed as percentage of cells over threshold after Bc2L-A stimulation (FL binder, n = 4; FL nonbinder, n = 4; HD, n = 7; box and whiskers). *P = .0286 (binder vs nonbinder), P = .242 (binder vs HD), P = .5237 (nonbinder vs HD). Data are representative of >3 independent experiments.