Peter Tobias Felixberger ^1,2 Geoffroy Andrieux ³ Andrea Maul-Pavicic ^1,2 Sigune Goldacker ^1,2 Ina Harder ^1,2 Sylvia Gutenberger ^1,2 Jonathan J. M. Landry ⁴ Vladimir Benes ⁴ Till Fabian Jakob ⁵ Melanie Boerries ^3,6 Lars Nitschke ⁷ Reinhard Edmund Voll ^1,2 Klaus Warnatz ^1,2* Baerbel Keller ^1,2*

• ¹ Department of Rheumatology and Clinical Immunology, Medical Center, University of Freiburg, Freiburg, Germany
• ² Center for Chronic Immunodeficiency, University of Freiburg Medical Center, Freiburg, Germany
• ³ Institute of Medical Bioinformatics and Systems Medicine, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg im Breisgau, Germany
• ⁴ Genomics Core Facility, European Molecular Biology Laboratory, Heidelberg, Germany
• ⁵ Department of Otorhinolaryngology - Head and Neck Surgery, University of Freiburg Medical Center, Freiburg, Baden-Württemberg, Germany
• ⁶ German Cancer Consortium (DKTK), Partner site Freiburg, a partnership between DKFZ and Medical Center - University of Freiburg, Freiburg im Breisgau, Germany
• ⁷ Division of Genetics, Department of Biology, University of Erlangen, Erlangen, Germany

The posttranslational modification of cellular macromolecules by glycosylation is considered to contribute to disease parthenogenesis in autoimmune and inflammatory conditions. In a subgroup of patients with common variable immunodeficiency (CVID), the occurrence of such complications is associated with an expansion of naïve-like CD21 low B cells during a chronic type 1 immune activation. The glycosylation pattern of CVID patients' B cells has not been addressed to date.The objective of this study was to examine the surface glycome of B cells in patients with CVID and immune dysregulation.We performed surface lectin staining of B cells from peripheral blood and tonsils ex vivo and after in vitro stimulation and examined the expression of glycosylation-related genes by RNAseq in naïve-like CD21 low B cells ex vivo and of naïve CD21 pos B cells of healthy controls after in vitro stimulation.Results: Unlike CD21 pos B cells, naïve-like CD21 low B cells from CVID patients and CD21 low B cells from healthy controls exhibited a unique glycosylation pattern with high levels of α2,6 sialic acids and fucose. This hypersialylation and hyperfucosylation was especially induced by activation via anti-IgM and interferon γ (IFNγ). Transcriptome analysis implied that naïve-like CD21 low B cells exhibit a comprehensively reorganized glycosylation machinery with anti-IgM/IFNγ having the potential to initiate these changes in vitro.: CD21 low B cells are hypersialylated and hyperfucosylated. Especially hypersialylation has been implied in altered receptor-ligand interactions potentially affecting CD21 low B-cell function. The glycome changes seem to be caused by the prominent type I immune response in complicated CVID patients. A better understanding of the consequences of the altered glycosylation on immune cell function might open new therapeutic strategies.