Figure 2
From: Reconstituted B cell receptor signaling reveals carbohydrate-dependent mode of activation
B cell IgM is heavily sialylated and binds to HA.
(A) Secreted B cell IgM was immunoisolated (silver stain, upper left) and the mu chain gel band was excised for MS analysis. The IgM LC MS/MS and analysis first confirmed the IgM protein sequence (lower left) and MALDI-TOF-MS was used to analysis the glycans cleaved using PNGase. The spectra for this carbohydrate analysis is presented along with a summary table of the glycan structures. Abbreviations: Hex = Hexose; HexNAc = N-acetylhexosamine; dHex= deoxyhexose; NeuNAc = N-acetylneuraminic acid (=sialic acid; bolded in the summary table). (B) SA-dependent binding to secreted IgM was confirmed by the interaction between non-cognate IgM and WT HA but not Y98F HA. This binding was assessed by ELISA and is presented is the mean and sem of three independent binding replicates.
