Optimal AID expression and efficient immunoglobulin class switch recombination are dependent on the hypoxia-inducible factor.

During immune responses, B cells engaging a cognate antigen are recruited to GCs in secondary lymphoid organs where they will diversify their BCR to generate highly specific and adapted humoral responses. They do so, by inducing the expression of activation-induced cytidine deaminase (AID), which initiates somatic hypermutation (SHM) and class switch recombination (CSR). AID deaminates cytosines in ss DNA, generating U:G mismatches that are processed to induce ds DNA break intermediates during CSR that result in the expression of a different antibody isotype. Interestingly, hypoxia regions have been reported in GCs and suggesting that hypoxia could modulate the humoral response. Furthermore, hypoxia inducible transcription factor (HIF) can bind to the AID promoter and induce AID expression in a non-B-cell setting, suggesting that it might be involved in the transcriptional induction of AID in B cells, hence, regulating SHM and CSR. We, thus, hypothesized that HIF could regulate the efficiency of CSR. Here, we show that the inactivation of both the HIF-1α and HIF-1ß subunits of the HIF transcription factor in murine CH12 B cells results in defective CSR and that this is due to the suboptimal induction of AID expression.

IgD shapes the pre-immune naïve B cell compartment in humans.

B cell maturation and immunoglobulin (Ig) repertoire selection are governed by expression of a functional B cell receptor (BCR). Naïve B cells co-express their BCR as IgM and IgD isotype. However, the role of the additionally expressed IgD on naïve B cells is not known. Here we assessed the impact of IgD on naïve B cell maturation and Ig repertoire selection in 8 individuals from 3 different families with heterozygous loss-of-function or loss-of expression mutations in IGHD. Although naïve B cells from these individuals expressed IgM on their surface, the IGHD variant in heterozygous state entailed a chimeric situation by allelic exclusion with almost half of the naïve B cell population lacking surface IgD expression. Flow cytometric analyses revealed a distinct phenotype of IgD-negative naïve B cells with decreased expression of CD19, CD20 and CD21 as well as lower BAFF-R and integrin-ß7 expression. IgD-negative B cells were less responsive in vitro after engaging the IgM-BCR, TLR7/9 or CD40 pathway. Additionally, a selective disadvantage of IgD-negative B cells within the T2 transitional and mature naïve B cell compartment as well as reduced frequencies of IgMlo/- B cells within the mature naïve B cell compartment lacking IgD were evident. RNA-Ig-seq of bulk sorted B cell populations showed an altered selection of distinct VH segments in the IgD-negative mature naïve B cell population. We conclude that IgD expression on human naïve B cells is redundant for generation of naïve B cells in general, but further shapes the naive B cell compartment starting from T2 transitional B cells. Our observations suggest an unexpected role of IgD expression to be critical for selection of distinct Ig VH segments into the pre-immune Ig repertoire and for the survival of IgMlo/- naïve B cells known to be enriched in poly-/autoreactive B cell clones.

Lineage tracing reveals B cell antibody class switching is stochastic, cell-autonomous, and tuneable.

To optimize immunity to pathogens, B lymphocytes generate plasma cells with functionally diverse antibody isotypes. By lineage tracing single cells within differentiating B cell clones, we identified the heritability of discrete fate controlling mechanisms to inform a general mathematical model of B cell fate regulation. Founder cells highly influenced clonal plasma-cell fate, whereas class switch recombination (CSR) was variegated within clones. In turn, these CSR patterns resulted from independent all-or-none expression of both activation-induced cytidine deaminase (AID) and IgH germline transcription (GLT), with the latter being randomly re-expressed after each cell division. A stochastic model premised on these molecular transition rules accurately predicted antibody switching outcomes under varied conditions in vitro and during an immune response in vivo. Thus, the generation of functionally diverse antibody types follows rules of autonomous cellular programming that can be adapted and modeled for the rational control of antibody classes for potential therapeutic benefit.

Improving naive B cell isolation by absence of CD45RB glycosylation and CD27 expression in combination with BCR isotype.

In past years ex vivo and in vivo experimental approaches involving human naive B cells have proven fundamental for elucidation of mechanisms promoting B cell differentiation in both health and disease. For such studies, it is paramount that isolation strategies yield a population of bona fide naive B cells, i.e., B cells that are phenotypically and functionally naive, clonally non-expanded, and have non-mutated BCR variable regions. In this study different combinations of common as well as recently identified B cell markers were compared to isolate naive B cells from human peripheral blood. High-throughput BCR sequencing was performed to analyze levels of somatic hypermutation and clonal expansion. Additionally, contamination from mature mutated B cells intrinsic to each cell-sorting strategy was evaluated and how this impacts the purity of obtained populations. Our results show that current naive B cell isolation strategies harbor contamination from non-naive B cells, and use of CD27-IgD+ is adequate but can be improved by including markers for CD45RB glycosylation and IgM. The finetuning of naive B cell classification provided herein will harmonize research lines using naive B cells, and will improve B cell profiling during health and disease, e.g. during diagnosis, treatment, and vaccination strategies.

CD45RB Glycosylation and Ig Isotype Define Maturation of Functionally Distinct B Cell Subsets in Human Peripheral Blood.

Glycosylation of CD45RB (RB+) has recently been identified to mark antigen-experienced B cells, independent of their CD27 expression. By using a novel combination of markers including CD45RB glycosylation, CD27 and IgM/IgD isotype expression we segregated human peripheral blood B cell subsets and investigated their IGHV repertoire and in vitro functionality. We observed distinct maturation stages for CD27-RB+ cells, defined by differential expression of non-switched Ig isotypes. CD27-RB+ cells, which only express IgM, were more matured in terms of Ig gene mutation levels and function as compared to CD27-RB+ cells that express both IgM and IgD or cells that were CD27-RB-. Moreover, CD27-RB+IgM+ cells already showed remarkable rigidity in IgM isotype commitment, different from CD27-RB+IgMD+ and CD27-RB- cells that still demonstrated great plasticity in B cell fate decision. Thus, glycosylation of CD45RB is indicative for antigen-primed B cells, which are, dependent on the Ig isotype, functionally distinct.

STAT5B restrains human B-cell differentiation to maintain humoral immune homeostasis.

BACKGROUND: Lymphocyte differentiation is regulated by coordinated actions of cytokines and signaling pathways. IL-21 activates STAT1, STAT3, and STAT5 and is fundamental for the differentiation of human B cells into memory cells and antibody-secreting cells. While STAT1 is largely nonessential and STAT3 is critical for this process, the role of STAT5 is unknown. OBJECTIVES: This study sought to delineate unique roles of STAT5 in activation and differentiation of human naive and memory B cells. METHODS: STAT activation was assessed by phospho-flow cytometry cell sorting. Differential gene expression was determined by RNA-sequencing and quantitative PCR. The requirement for STAT5B in B-cell and CD4+ T-cell differentiation was assessed using CRISPR-mediated STAT5B deletion from B-cell lines and investigating primary lymphocytes from individuals with germline STAT5B mutations. RESULTS: IL-21 activated STAT5 and strongly induced SOCS3 in human naive, but not memory, B cells. Deletion of STAT5B in B-cell lines diminished IL-21-mediated SOCS3 induction. PBMCs from STAT5B-null individuals contained expanded populations of immunoglobulin class-switched B cells, CD21loTbet+ B cells, and follicular T helper cells. IL-21 induced greater differentiation of STAT5B-deficient B cells into plasmablasts in vitro than B cells from healthy donors, correlating with higher expression levels of transcription factors promoting plasma cell formation. CONCLUSIONS: These findings reveal novel roles for STAT5B in regulating IL-21-induced human B-cell differentiation. This is achieved by inducing SOCS3 to attenuate IL-21 signaling, and BCL6 to repress class switching and plasma cell generation. Thus, STAT5B is critical for restraining IL-21-mediated B-cell differentiation. These findings provide insights into mechanisms underpinning B-cell responses during primary and subsequent antigen encounter and explain autoimmunity and dysfunctional humoral immunity in STAT5B deficiency.

Late Inflammation Induced by Asbestiform Fibers in Mice Is Ameliorated by a Small Molecule Synthetic Lignan.

Exposure to Libby amphibole (LA) asbestos-like fibers is associated with increased risk of asbestosis, mesothelioma, pulmonary disease, and systemic autoimmune disease. LGM2605 is a small molecule antioxidant and free radical scavenger, with anti-inflammatory effects in various disease models. The current study aimed to determine whether the protective effects of LGM2605 persist during the late inflammatory phase post-LA exposure. Male and female C57BL/6 mice were administered daily LGM2605 (100 mg/kg) via gel cups for 3 days before and 14 days after a 200 µg LA given via intraperitoneal (i.p.) injection. Control mice were given unsupplemented gel cups and an equivalent dose of i.p. saline. On day 14 post-LA treatment, peritoneal lavage was assessed for immune cell influx, cytokine concentrations, oxidative stress biomarkers, and immunoglobulins. During the late inflammatory phase post-LA exposure, we noted an alteration in trafficking of both innate and adaptive immune cells, increased pro-inflammatory cytokine concentrations, induction of immunoglobulin isotype switching, and increased oxidized guanine species. LGM2605 countered these changes similarly among male and female mice, ameliorating late inflammation and altering immune responses in late post-LA exposure. These data support possible efficacy of LGM2605 in the prolonged treatment of LA-associated disease and other inflammatory conditions.

The IgE Blocking Activity Induced by Dermatophagoides pteronyssinus Subcutaneous Immunotherapy Does Not Correlate with Specific IgA but with IgG4 in both Serum and Saliva.

BACKGROUND: The role of salivary-specific IgG4 and IgA in subcutaneous immunotherapy (SCIT) is not well defined. We aimed to investigate the change of IgG4 and IgA in both serum and saliva and their correlations with IgE-blocking-factor (IgE-BF) during SCIT. METHOD: 307 Dermatophagoides pteronyssinus (DP) allergic rhinitis and/or asthma patients were recruited for this study. 286 patients received DP-SCIT for 1 year. Twenty-one patients received only symptomatic treatment. DP-, Der p 1-, and Der p 2-specific IgE in serum, specific-IgG4 and Der p 2-specific IgA1 and IgA2 in both serum and saliva were measured at timepoints 0, 4, and 12 months during DP-SCIT. Correlation between salivary and serological IgG4, IgA, and their correlation with DP-specific IgE-BF measured in serum was evaluated. RESULTS: During DP-SCIT, the allergen-specific IgG4 in both saliva and serum increased and correlated significantly, the correlation becomes stronger over the treatment time. DP-specific IgE-BF significantly correlated with DP-specific IgG4 in serum (p < 0.0001) at different timepoints and in saliva at 12 months of SCIT (p < 0.01). No change in Der p 2-specific IgA during DP-SCIT was observed, and the IgA in serum did not correlate with IgA in saliva. There was no correlation between DP IgE-BF and Der p 2-specific IgA in serum or saliva. The control group did not exhibit significant changes in any antibody level measured. CONCLUSION: The IgE blocking activity induced by DP-SCIT treatment correlated with specific IgG4 and not IgA. The IgG4 in saliva correlates with serum IgG4 and can be an alternative immunological marker beyond 1 year of SCIT treatment.

Immunoglobulin isotype compositions of ABO specific antibodies are dependent on the individual patient blood group and blood group specificity: Results from a healthy donor cohort.

Antibodies specific for the blood group ABO system antigens are of clinical significance and immunological interest. Routine clinical methods typically employ direct or indirect haemagglutination methods to measure IgM and IgG, respectively. We have developed a simple, single tube method to quantify IgM, IgG, and IgA specific for A and B antigens in order to improve accuracy and reproducibility, and to investigate the relationships between ABO group antibody type, and antibody level. Plasma samples from 300 healthy blood donors were studied. Levels of IgM and IgG binding to reagent group A and B red cells were measure by agglutination (HA) and multi-colour flow cytometry (MC-FC). IgA was also measured by MC-FC. Our FC method was found to be significantly more reproducible than HA for the measurement of blood group A and B specific antibodies. We found statistically significant correlations between antibodies measured by GC-HA and MC-FC, but sufficient differences to indicate that these methods are not equivalent. By MC-FC, IgM, IgG and IgA levels and isotope profiles were found to be dependent on both the donor ABO type and the specificity of the antibody. This study demonstrated heterogeneity in the immunoglobulin class profiles of ABO-blood group specific antibodies within the healthy population. Differences in isotype profiles of ABO-blood group specific antibodies may indicate fundamental differences in the immune mechanisms that generate these antibodies. This is likely to be relevant to the clinical situations where management or diagnosis depend on ABO-specific antibody detection and measurement.

Kinetics of IgG subclasses and their effects on the incidence of infection after allogeneic hematopoietic stem cell transplantation.

BACKGROUND: The impact of the reconstitution of IgG subclasses after allogeneic hematopoietic cell transplantation (allo-HCT) on the outcomes is unclear. METHODS: We investigated the effects of stem cell source on the levels of serum IgG subclasses and their influence on the infection risk and prognosis. The levels of serum IgG, IgG2 and IgG4 were measured chronologically in 100 patients who underwent allo-HCT at our institute. RESULTS: The median levels of serum IgG, IgA and IgM and the number of total B-cells were determined up to one year after allo-HCT. The serum IgG2 levels decreased within one year. A multiple linear regression analysis identified lymphoid malignancy, cord blood, and days after allo-HCT as significant risk factors for low serum IgG2 levels. There were no significant differences in the level of IgG or IgG2 at 90 days after allo-HCT between the late bacterial infection group (≥90 days following allo-HCT) and the control group (P = 0.34 and 0.45, respectively). There was no significant impact of the IgG, IgG2 or IgG4 levels on the survival or non-relapse mortality. CONCLUSION: The results suggest that cord blood transplantation might affect humoral immune reconstitution, including the IgG2 level, after allo-HCT.

Impact of Immunoglobulin Isotype and Epitope on the Functional Properties of Vibrio cholerae O-Specific Polysaccharide-Specific Monoclonal Antibodies.

Vibrio cholerae causes the severe diarrheal disease cholera. Clinical disease and current oral cholera vaccines generate antibody responses associated with protection. Immunity is thought to be largely mediated by lipopolysaccharide (LPS)-specific antibodies, primarily targeting the O-antigen. However, the properties and protective mechanism of functionally relevant antibodies have not been well defined. We previously reported on the early B cell response to cholera in a cohort of Bangladeshi patients, from which we characterized a panel of human monoclonal antibodies (MAbs) isolated from acutely induced plasmablasts. All antibodies in that previous study were expressed in an IgG1 backbone irrespective of their original isotype. To clearly determine the impact of affinity, immunoglobulin isotype and subclass on the functional properties of these MAbs, we re-engineered a subset of low- and high-affinity antibodies in different isotype and subclass immunoglobulin backbones and characterized the impact of these changes on binding, vibriocidal, agglutination, and motility inhibition activity. While the high-affinity antibodies bound similarly to O-antigen, irrespective of isotype, the low-affinity antibodies displayed significant avidity differences. Interestingly, despite exhibiting lower binding properties, variants derived from the low-affinity MAbs had comparable agglutination and motility inhibition properties to the potently binding antibodies, suggesting that how the MAb binds to the O-antigen may be critical to function. In addition, not only pentameric IgM and dimeric IgA, but also monomeric IgA, was remarkably more potent than their IgG counterparts at inhibiting motility. Finally, analyzing highly purified F(ab) versions of these antibodies, we show that LPS cross-linking is essential for motility inhibition.IMPORTANCE Immunity to the severe diarrheal disease cholera is largely mediated by lipopolysaccharide (LPS)-specific antibodies. However, the properties and protective mechanisms of functionally relevant antibodies have not been well defined. Here, we have engineered low and high-affinity LPS-specific antibodies in different immunoglobulin backbones in order to assess the impact of affinity, immunoglobulin isotype, and subclass on binding, vibriocidal, agglutination, and motility inhibition functional properties. Importantly, we found that affinity did not directly dictate functional potency since variants derived from the low-affinity MAbs had comparable agglutination and motility inhibition properties to the potently binding antibodies. This suggests that how the antibody binds sterically may be critical to function. In addition, not only pentameric IgM and dimeric IgA, but also monomeric IgA, was remarkably more potent than their IgG counterparts at inhibiting motility. Finally, analyzing highly purified F(ab) versions of these antibodies, we show that LPS cross-linking is essential for motility inhibition.

New Insights into IgZ as a Maternal Transfer Ig Contributing to the Early Defense of Fish against Pathogen Infection.

IgZ or its equivalent IgT is a newly discovered teleost specific Ig class that is highly specialized in mucosal immunity. However, whether this IgZ/IgT class participates in other biological processes remains unclear. In this study, we unexpectedly discovered that IgZ is highly expressed in zebrafish ovary, accumulates in unfertilized eggs, and is transmitted to offspring from eggs to zygotes. Maternally transferred IgZ in zygotes is found at the outer and inner layers of chorion, perivitelline space, periphery of embryo body, and yolk, providing different lines of defense against pathogen infection. A considerable number of IgZ+ B cells are found in ovarian connective tissues distributed between eggs. Moreover, pIgR, the transporter of IgZ, is also expressed in the ovary and colocalizes with IgZ in the zona radiata of eggs. Thus, IgZ is possibly secreted by ovarian IgZ+ B cells and transported to eggs through association with pIgR in a paracrine manner. Maternal IgZ in zygotes showed a broad bacteriostatic activity to different microbes examined, and this reactivity can be manipulated by orchestrating desired bacteria in water where parent fish live or immunizing the parent fish through vaccination. These observations suggest that maternal IgZ may represent a group of polyclonal Abs, providing protection against various environmental microbes encountered by a parent fish that were potentially high risk to offspring. To our knowledge, our findings provide novel insights into a previously unrecognized functional role of IgZ/IgT Ig in the maternal transfer of immunity in fish, greatly enriching current knowledge about this ancient Ig class.

PD-1-specific "Blocking" antibodies that deplete PD-1+ T cells present an inconvenient variable in preclinical immunotherapy experiments.

Therapeutic antibodies blocking PD-1-/PD-L1 interaction have achieved remarkable clinical success in cancer. In addition to blocking a target molecule, some isotypes of antibodies can activate complement, NK cells or phagocytes, resulting in death of the cell expressing the antibody's target. Human anti-PD-1 therapeutics use antibody isotypes designed to minimize such antibody-dependent lysis. In contrast, anti-PD-1 reagents used in mice are derived from multiple species, with different isotypes, and are not engineered to reduce target cell death: few studies analyze or discuss how antibody species and isotype may impact data interpretation. We demonstrate here that anti-PD-1 therapy to promote activation and proliferation of murine PD-1-expressing CD8 T cells sometimes led instead to a loss of antigen specific cells. This phenomenon was seen in two tumor models and a model of virus infection, and varied with the clone of anti-PD-1 antibody. Additionally, we compared competition among anti-PD-1 clones to find a combination that allows detection of PD-1-expressing cells despite the presence of blocking anti-PD1 antibodies in vivo. These data bring attention to the possibility of unintended target cell depletion with some commonly used anti-mouse PD-1 clones, and should provide a valuable resource for the design and interpretation of anti-PD-1 studies in mice.

Identifying novel B-cell targets for chronic inflammatory autoimmune disease by screening of chemical probes in a patient-derived cell assay.

B-cell secretion of autoantibodies drives autoimmune diseases, including systemic lupus erythematosus and idiopathic inflammatory myositis. Few therapies are presently available for treatment of these patients, often resulting in unsatisfactory effects and helping only some of the patients. We developed a screening assay for evaluation of novel targets suspending B-cell maturation into antibody secreting cells, which could contribute to future drug development. The assay was employed for testing 43 high quality chemical probes and compounds inhibiting under-explored protein targets, using primary cells from patients with autoimmune disease. Probes inhibiting bromodomain family proteins and histone methyl transferases demonstrated abrogation of B-cell functions to a degree comparable to a positive control, the JAK inhibitor tofacitinib. Inhibition of each target rendered a specific functional cell and potential disease modifying effect, indicating specific epigenetic protein targets as potential new intervention points for future drug discovery and development efforts.

Allergome-wide peptide microarrays enable epitope deconvolution in allergen-specific immunotherapy.

BACKGROUND: The interaction of allergens and allergen-specific IgE initiates the allergic cascade after crosslinking of receptors on effector cells. Antibodies of other isotypes may modulate such a reaction. Receptor crosslinking requires binding of antibodies to multiple epitopes on the allergen. Limited information is available on the complexity of the epitope structure of most allergens. OBJECTIVES: We sought to allow description of the complexity of IgE, IgG4, and IgG epitope recognition at a global, allergome-wide level during allergen-specific immunotherapy (AIT). METHODS: We generated an allergome-wide microarray comprising 731 allergens in the form of more than 172,000 overlapping 16-mer peptides. Allergen recognition by IgE, IgG4, and IgG was examined in serum samples collected from subjects undergoing AIT against pollen allergy. RESULTS: Extensive induction of linear peptide-specific Phl p 1- and Bet v 1-specific humoral immunity was demonstrated in subjects undergoing a 3-year-long AIT against grass and birch pollen allergy, respectively. Epitope profiles differed between subjects but were largely established already after 1 year of AIT, suggesting that dominant allergen-specific antibody clones remained as important contributors to humoral immunity following their initial establishment during the early phase of AIT. Complex, subject-specific patterns of allergen isoform and group cross-reactivities in the repertoires were observed, patterns that may indicate different levels of protection against different allergen sources. CONCLUSIONS: The study highlights the complexity and subject-specific nature of allergen epitopes recognized following AIT. We envisage that epitope deconvolution will be an important aspect of future efforts to describe and analyze the outcomes of AIT in a personalized manner.

Immunoglobulins with Non-Canonical Functions in Inflammatory and Autoimmune Disease States.

Immunoglobulins are known to combine various effector mechanisms of the adaptive and the innate immune system. Classical immunoglobulin functions are associated with antigen recognition and the initiation of innate immune responses. However, in addition to classical functions, antibodies exhibit a variety of non-canonical functions related to the destruction of various pathogens due to catalytic activity and cofactor effects, the action of antibodies as agonists/antagonists of various receptors, the control of bacterial diversity of the intestine, etc. Canonical and non-canonical functions reflect the extreme human antibody repertoire and the variety of antibody types generated in the organism: antigen-specific, natural, polyreactive, broadly neutralizing, homophilic, bispecific and catalytic. The therapeutic effects of intravenous immunoglobulins (IVIg) are associated with both the canonical and non-canonical functions of antibodies. In this review, catalytic antibodies will be considered in more detail, since their formation is associated with inflammatory and autoimmune diseases. We will systematically summarize the diversity of catalytic antibodies in normal and pathological conditions. Translational perspectives of knowledge about natural antibodies for IVIg therapy will be also discussed.

An Integrated Multi-omic Single-Cell Atlas of Human B Cell Identity.

B cells are capable of a wide range of effector functions including antibody secretion, antigen presentation, cytokine production, and generation of immunological memory. A consistent strategy for classifying human B cells by using surface molecules is essential to harness this functional diversity for clinical translation. We developed a highly multiplexed screen to quantify the co-expression of 351 surface molecules on millions of human B cells. We identified differentially expressed molecules and aligned their variance with isotype usage, VDJ sequence, metabolic profile, biosynthesis activity, and signaling response. Based on these analyses, we propose a classification scheme to segregate B cells from four lymphoid tissues into twelve unique subsets, including a CD45RB+CD27- early memory population, a class-switched CD39+ tonsil-resident population, and a CD19hiCD11c+ memory population that potently responds to immune activation. This classification framework and underlying datasets provide a resource for further investigations of human B cell identity and function.

Immunoglobulin G Subclass-Specific Glycosylation Changes in Primary Epithelial Ovarian Cancer.

Epithelial ovarian cancer (EOC) was previously shown to be associated with glycosylation changes of total serum and total IgG proteins. However, as a majority of previous studies analyzed released glycan profiles, still little is known about IgG subclass-specific alterations in ovarian cancer. Hence, in this study, we investigated EOC-related glycosylation changes of the three most abundant IgG subclasses, namely, IgG1, IgG2 and IgG3 isolated from sera of 87 EOC patients and 74 age-matched healthy controls. In order to separate IgG2 and IgG3, we performed a two-step affinity purification employing Protein A and Protein G Sepharose. After tryptic digestion, IgG glycopeptides were enriched and measured by MALDI-TOF-MS. Finally, EOC-related glycosylation changes were monitored at the level of total agalactosylation, monogalactosylation, digalactosylation, sialylation, bisection and fucosylation, which were calculated separately for each IgG subclass. Interestingly, aside from an EOC-related increase in agalactosylation/decrease in monogalactosylation and digalactosylation observed in all IgG subclasses, some subclass-specific trends were detected. Glycosylation of IgG1 was found to be most strongly affected in EOC, as it exhibited the highest number of significant differences between healthy controls and EOC patients. Specifically, IgG1 was the only subclass that showed a significant decrease in sialylation and a significant increase in fucosylation in EOC patients. Interestingly, IgG2 and IgG3 that were often investigated collectively in previous studies, were found to have distinct glycosylation patterns. IgG3 displayed stronger EOC-related increase in agalactosylation/decrease in digalactosylation and was characterized by notably higher sialylation, which consequently decreased in EOC patients. In conclusion, our study indicates that IgG subclasses exhibit subtly distinct glycosylation patterns of EOC-related alterations and that IgG1 and IgG3 agalactosylation show the strongest association with CA125, the routine diagnostic marker. Additionally, our results show that simultaneous analyses of IgG2 and IgG3 might lead to wrong conclusions as these two subclasses exhibit noticeably different glycosylation phenotypes.