IgA displays site- and subclass-specific glycoform differences despite equal glycoenzyme expression.

Area of Science:

• Immunology
• Glycobiology
• Biochemistry

Background:

• Glycosylation is a critical posttranslational modification for protein function.
• Immunoglobulin A (IgA) has N- and O-glycosylation sites, but its glycosylation is less understood than IgG.
• IgA1 and IgA2 exhibit functional and glycosylation differences, with IgA2 linked to autoimmune diseases and showing reduced sialylation, galactosylation, fucosylation, and bisection.

Purpose of the Study:

• To investigate the detailed glycosylation differences between IgA1 and IgA2.
• To explore the underlying mechanisms regulating these glycosylation variations.
• To understand the site-specific glycosylation patterns within IgA subclasses.

Main Methods:

• Isolation of IgA1 and IgA2 from healthy donor serum.
• Site-specific glycosylation analysis using mass spectrometry.
• Investigation of human bone marrow plasma cells via single-cell mRNA sequencing, flow cytometry, and ELISpot.

Main Results:

• Significant differences in glycoform abundance between IgA1 and IgA2 were observed.
• IgA2 glycans presented a more immature phenotype, with higher oligomannose prevalence and fewer processed glycans.
• Equal enzyme expression in IgA1 and IgA2 producing plasma cells suggests structural accessibility, not enzyme machinery, primarily drives glycosylation differences.

Conclusions:

• A class, subclass, and site-specific glycosylation fingerprint exists for IgA1 and IgA2.
• Structural differences in the protein backbones are the most probable cause for these distinct glycosylation patterns.