Intravenous immunoglobulin contains a broad repertoire of anticarbohydrate antibodies that is not restricted to the IgG₂ subclass

Background: Specificities for carbohydrate IgG antibodies, thought to be predominantly of the IgG₂ subclass, have never been broadly examined in healthy human subjects. Objective: To examine commercial intravenous immunoglobulin (IVIG) preparations for their ability to recognize a wide range of glycans and to determine the contribution of IgG₂ to the binding pattern observed. Methods: We used a glycan microarray to evaluate IVIG preparations and a control mix of similar proportions of human myeloma IgG₁ and IgG₂ for binding to 377 glycans, courtesy of the Consortium for Functional Glycomics Core H. Glycans recognized were categorized using public databases for their likely cellular sources. IgG₂ was depleted from IVIG by using immunoaffinity chromatography, and depletion was confirmed by using nephelometry and surface plasmon resonance. Results: Nearly half of the glycans bound IgG. Some of the glycans with the greatest antibody binding can be found in structures of human pathogenic bacteria (eg, Streptococcus pneumoniae, Mycobacterium tuberculosis, Vibrio cholera) and nonpathogenic bacteria, including LPS and lipoteichoic acid, capsular polysaccharides, and exopolysaccharides. Surprisingly, depletion of IgG₂ had only a modest effect on anticarbohydrate recognition patterns compared with the starting IVIG preparation. Little to no binding activity was detected to human endogenous glycans, including tumor-associated antigens. Conclusions: This novel, comprehensive analysis provides evidence that IVIG contains a much wider range than previously appreciated of anticarbohydrate IgG antibodies, including those recognizing both pathogenic and non-pathogen-associated prokaryotic glycans.