A pilot study showing differences in glycosylation patterns of IgG subclasses induced by pneumococcal, meningococcal, and two types of influenza vaccines

Regulators of placental antibody transfer through a modeling lens

Infants are vulnerable to infections owing to a limited ability to mount a humoral immune response and their tolerogenic immune phenotype, which has impeded the success of newborn vaccination. Transplacental transfer of IgG from mother to fetus provides crucial protection in the first weeks of life, and maternal immunization has recently been implemented as a public health strategy to protect newborns against serious infections. Despite their early success, current maternal vaccines do not provide comparable protection across pregnancies with varying gestational lengths and placental and maternal immune features, and they do not account for the dynamic interplay between the maternal immune response and placental transfer. Moreover, progress toward the rational design of maternal vaccines has been hindered by inadequacies of existing experimental models and safety challenges of investigating longitudinal dynamics of IgG transfer in pregnant humans. Alternatively, in silico mechanistic models are a logical framework to disentangle the processes regulating placental antibody transfer. This Review synthesizes current literature through a mechanistic modeling lens to identify placental and maternal regulators of antibody transfer, their clinical covariates, and knowledge gaps to guide future research. We also describe opportunities to use integrated modeling and experimental approaches toward the rational design of vaccines against existing and emerging neonatal pathogen threats.

Immune Cells, Gut Microbiota, and Vaccines: A Gender Perspective

The development of preventive and therapeutic vaccines has played a crucial role in preventing infections and treating chronic and non-communicable diseases, respectively. For a long time, the influence of sex differences on modifying health and disease has not been addressed in clinical and preclinical studies. The interaction of genetic, epigenetic, and hormonal factors plays a role in the sex-related differences in the epidemiology of diseases, clinical manifestations, and the response to treatment. Moreover, sex is one of the leading factors influencing the gut microbiota composition, which could further explain the different predisposition to diseases in men and women. In the same way, differences between sexes occur also in the immune response to vaccines. This narrative review aims to highlight these differences, focusing on the immune response to vaccines. Comparative data about immune responses, vaccine effectiveness, and side effects are reviewed. Hence, the intricate interplay between sex, immunity, and the gut microbiota will be discussed for its potential role in the response to vaccination. Embracing a sex-oriented perspective in research may improve the efficacy of the immune response and allow the design of tailored vaccine schedules.

Unveiling the multifaceted landscape of N-glycosylation in antibody variable domains: Insights and implications

N-glycosylation at the antibody variable domain has emerged as an important modification influencing antibody function. Despite its significance, information regarding its role and regulation remains limited. To address this gap, we comprehensively explored antibody structures housing N-glycosylation within the Protein Data Bank, yielding fresh insights into this intricate landscape. Our findings revealed that among 208 structures, N-glycosylation was more prevalent in human and mouse antibodies containing IGHV1-8 and IGHV2-2 germline genes, respectively. Moreover, our research highlights the potential for somatic hypermutation to introduce N-glycosylation sites by substituting polar residues (Ser or Thr) in germline variable genes with asparagine. Notably, our study underscores the prevalence of N-glycosylation in antiviral antibodies, especially anti-HIV. Besides antigen-antibody interaction, our findings suggest that N-glycosylation may impact antibody specificity, affinity, and avidity by influencing Fab dimer formation and complementary-determining region orientation. We also identified different glycan structures in HIV and SARS-CoV-2 antibody proteomic datasets, highlighting disparities from the N-glycan structures between PDB antibodies and biological repertoires further highlighting the complexity of N-glycosylation patterns. Our findings significantly enrich our understanding of the N-glycosylation's multifaceted characteristics within the antibody variable domain. Additionally, they underscore the pressing imperative for a more comprehensive characterization of its impact on antibody function.

Quantitative mechanistic model reveals key determinants of placental IgG transfer and informs prenatal immunization strategies

Transplacental antibody transfer is crucially important in shaping neonatal immunity. Recently, prenatal maternal immunization has been employed to boost pathogen-specific immunoglobulin G (IgG) transfer to the fetus. Multiple factors have been implicated in antibody transfer, but how these key regulators work together to elicit selective transfer is pertinent to engineering vaccines for mothers to optimally immunize their newborns. Here, we present the first quantitative mechanistic model to uncover the determinants of placental antibody transfer and inform personalized immunization approaches. We identified placental FcγRIIb expressed by endothelial cells as a limiting factor in receptor-mediated transfer, which plays a key role in promoting preferential transport of subclasses IgG1, IgG3, and IgG4, but not IgG2. Integrated computational modeling and in vitro experiments reveal that IgG subclass abundance, Fc receptor (FcR) binding affinity, and FcR abundance in syncytiotrophoblasts and endothelial cells contribute to inter-subclass competition and potentially inter- and intra-patient antibody transfer heterogeneity. We developed an in silico prenatal vaccine testbed by combining a computational model of maternal vaccination with this placental transfer model using the tetanus, diphtheria, and acellular pertussis (Tdap) vaccine as a case study. Model simulations unveiled precision prenatal immunization opportunities that account for a patient's anticipated gestational length, placental size, and FcR expression by modulating vaccine timing, dosage, and adjuvant. This computational approach provides new perspectives on the dynamics of maternal-fetal antibody transfer in humans and potential avenues to optimize prenatal vaccinations that promote neonatal immunity.

Comparative analysis of spike-specific IgG Fc glycoprofiles elicited by adenoviral, mRNA, and protein-based SARS-CoV-2 vaccines

IgG antibodies are important mediators of vaccine-induced immunity through complement- and Fc receptor-dependent effector functions. Both are influenced by the composition of the conserved N-linked glycan located in the IgG Fc domain. Here, we compared the anti-Spike (S) IgG1 Fc glycosylation profiles in response to mRNA, adenoviral, and protein-based COVID-19 vaccines by mass spectrometry (MS). All vaccines induced a transient increase of antigen-specific IgG1 Fc galactosylation and sialylation. An initial, transient increase of afucosylated IgG was induced by membrane-encoding S protein formulations. A fucose-sensitive ELISA for antigen-specific IgG (FEASI) exploiting FcγRIIIa affinity for afucosylated IgG was used as an orthogonal method to confirm the LC-MS-based afucosylation readout. Our data suggest that vaccine-induced anti-S IgG glycosylation is dynamic, and although variation is seen between different vaccine platforms and individuals, the evolution of glycosylation patterns display marked overlaps.

Afucosylated IgG responses in humans - structural clues to the regulation of humoral immunity

Healthy immune responses require efficient protection without excessive inflammation. Recent discoveries on the degree of fucosylation of a human N-linked glycan at a conserved site in the immunoglobulin IgG-Fc domain might add an additional regulatory layer to adaptive humoral immunity. Specifically, afucosylation of IgG-Fc enhances the interaction of IgG with FcγRIII and thereby its activity. Although plasma IgG is generally fucosylated, afucosylated IgG is raised in responses to enveloped viruses and Plasmodium falciparum proteins expressed on infected erythrocytes, as well as during alloimmune responses. Moreover, while afucosylation can exacerbate some infectious diseases (e.g., COVID-19), it also correlates with traits of protective immunity against malaria and HIV-1. Herein we discuss the implications of IgG afucosylation for health and disease, as well as for vaccination.

A functional spleen contributes to afucosylated IgG in humans

As a lymphoid organ, the spleen hosts a wide range of immune cell populations, which not only remove blood-borne antigens, but also generate and regulate antigen-specific immune responses. In particular, the splenic microenvironment has been demonstrated to play a prominent role in adaptive immune responses to enveloped viral infections and alloantigens. During both types of immunizations, antigen-specific immunoglobulins G (IgGs) have been characterized by the reduced amount of fucose present on N-linked glycans of the fragment crystallizable (Fc) region. These glycans are essential for mediating the induction of immune effector functions. Therefore, we hypothesized that a spleen may modulate humoral responses and serve as a preferential site for afucosylated IgG responses, which potentially play a role in immune thrombocytopenia (ITP) pathogenesis. To determine the role of the spleen in IgG-Fc glycosylation, we performed IgG subclass-specific liquid chromatography-mass spectrometry (LC-MS) analysis of Fc glycosylation in a large cohort of individuals splenectomized due to trauma, due to ITP, or spherocytosis. IgG-Fc fucosylation was consistently increased after splenectomy, while no effects for IgG-Fc galactosylation and sialylation were observed. An increase in IgG1- and IgG2/3-Fc fucosylation level upon splenectomy has been reported here for the first time, suggesting that immune responses occurring in the spleen may be particularly prone to generate afucosylated IgG responses. Surprisingly, the level of total IgG-Fc fucosylation was decreased in ITP patients compared to healthy controls. Overall, our results suggest a yet unrecognized role of the spleen in either the induction or maintenance of afucosylated IgG responses by B cells.

Afucosylated Plasmodium falciparum-specific IgG is induced by infection but not by subunit vaccination

Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) family members mediate receptor- and tissue-specific sequestration of infected erythrocytes (IEs) in malaria. Antibody responses are a central component of naturally acquired malaria immunity. PfEMP1-specific IgG likely protects by inhibiting IE sequestration and through IgG-Fc Receptor (FcγR) mediated phagocytosis and killing of antibody-opsonized IEs. The affinity of afucosylated IgG to FcγRIIIa is up to 40-fold higher than fucosylated IgG, resulting in enhanced antibody-dependent cellular cytotoxicity. Most IgG in plasma is fully fucosylated, but afucosylated IgG is elicited in response to enveloped viruses and to paternal alloantigens during pregnancy. Here we show that naturally acquired PfEMP1-specific IgG is strongly afucosylated in a stable and exposure-dependent manner, and efficiently induces FcγRIIIa-dependent natural killer (NK) cell degranulation. In contrast, immunization with a subunit PfEMP1 (VAR2CSA) vaccine results in fully fucosylated specific IgG. These results have implications for understanding protective natural- and vaccine-induced immunity to malaria.

Here, Larsen et al. describe differences in Fc fucosylation of P. falciparum PfEMP1-specific IgG produced in response to natural infection versus VAR2CSA-type subunit vaccination, which leads to differences in the ability to induce FcγRIIIa-dependent natural killer cell degranulation.

Afucosylated Plasmodium falciparum-specific IgG is induced by infection but not by subunit vaccination

Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) family members mediate receptor- and tissue-specific sequestration of infected erythrocytes (IEs) in malaria. Antibody responses are a central component of naturally acquired malaria immunity. PfEMP1-specific IgG likely protects by inhibiting IE sequestration and through IgG-Fc Receptor (FcγR) mediated phagocytosis and killing of antibody-opsonized IEs. The affinity of afucosylated IgG to FcγRIIIa is up to 40-fold higher than fucosylated IgG, resulting in enhanced antibody-dependent cellular cytotoxicity. Most IgG in plasma is fully fucosylated, but afucosylated IgG is elicited in response to enveloped viruses and to paternal alloantigens during pregnancy. Here we show that naturally acquired PfEMP1-specific IgG is strongly afucosylated in a stable and exposure-dependent manner, and efficiently induces FcγRIIIa-dependent natural killer (NK) cell degranulation. In contrast, immunization with a subunit PfEMP1 (VAR2CSA) vaccine results in fully fucosylated specific IgG. These results have implications for understanding protective natural- and vaccine-induced immunity to malaria.

Association of Antibody-Dependent Neutrophil Phagocytosis With Distinct Antibody Glycosylation Profiles Following Typhoid Vaccination

Typhoid Vi-conjugate vaccines (Vi-TCV) have been developed to control typhoid fever in children in endemic regions. Previously, in a human challenge model of typhoid, Vi-TCV was administered prior to deliberate ingestion of Salmonella Typhi by healthy adult volunteers in the UK. Vi-specific antibody-dependent neutrophil phagocytosis (ADNP) was associated with protection against enteric fever in this model, but it is not known if ADNP is induced by vaccination of children. We measured ADNP in a cohort of Nepalese children receiving a Vi-TCV in a field study to investigate whether functional antibody responses were also present in children in an endemic setting. Furthermore, we investigated relationships between the functional antibody measures and other properties of the antibody response, including Vi-IgG and IgA titres, and Fc region glycosylation. Antibody-dependent neutrophil phagocytosis significantly increased in children aged 9 months to 15 years between the day of vaccination and 28 days following administration of Vi-TCV (D28). The magnitude of ADNP was also comparable with the levels of ADNP induced by plasma from vaccinated UK adults. Neither IgG nor IgA antibody titres significantly correlated with ADNP scores at D28; however, increased vaccine-induced ADNP was associated with decreased levels of IgG1 sialylation. These data suggest that vaccination with Vi-TCV produces functional antibody responses in children, which associate with specific glycosylation patterns of the Fc region.

Proatherogenic Sialidases and Desialylated Lipoproteins: 35 Years of Research and Current State from Bench to Bedside

This review summarizes the main achievements in basic and clinical research of atherosclerosis. Focusing on desialylation as the first and the most important reaction of proatherogenic pathological cascade, we speak of how desialylation increases the atherogenic properties of low density lipoproteins and decreases the anti-atherogenic properties of high density lipoproteins. The separate sections of this paper are devoted to immunogenicity of lipoproteins, the enzymes contributing to their desialylation and animal models of atherosclerosis. In addition, we evaluate the available experimental and diagnostic protocols that can be used to develop new therapeutic approaches for atherosclerosis.

Glycosylation is required for the neutralizing activity of human IgG1 antibodies against human rabies induced by pre-exposure prophylaxis

Rabies lyssavirus (RABV) neutralizing IgG antibodies confer protection after rabies vaccination, although how the RABV-specific antibodies neutralize the virus is still unknown. As changes in the antibody's carbohydrate chain can interfere with its effector functions, we compared the glycosylation patterns of both neutralizing and non-neutralizing IgG1 induced by pre-exposure prophylaxis to human rabies and analyzed their influence on in vitro antibody neutralizing activities. Specific IgG1 were purified from human serum using affinity chromatography. Purity and avidity were analyzed by SDS-PAGE and indirect ELISA using NH₄SCN respectively. The N-linked oligosaccharide chain of the purified IgG antibody was evaluated using a lectin-based ELISA assay with a panel of seven lectins. The activity of purified IgG1 and neutralizing IgG1 deglycosylated by PNGase F enzyme were analyzed using the rapid fluorescent focus inhibition test. The purified IgG1 showed an electrophoretic pattern compatible with human IgG. All of the antibodies recognized RABV, although neutralizing IgG1 had a higher avidity (RAI = 80%) than non-neutralizing IgG1 (RAI = 30%). The neutralizing IgG1 also showed higher binding to WFA, ECA, WGA, and ConA lectins, indicating possible different N-acetylgalactosamine, galactose, N-acetylglucosamine, and mannose contents. Non-neutralizing IgG1, on the other hand, showed strong binding at UEA-1 and SNA, which bind to fucose and sialic acid residues respectively. Different glycosylation profiles were also observed in Fab and Fc fragments from neutralizing and non-neutralizing IgG1, although the deglycosylated IgG1 lost its neutralizing activity. Our results suggest that antibody glycosylation is important for neutralizing RABV in vitro, since neutralizing IgG1 has a different glycosylation profile than non-neutralizing IgG1. Further research will be needed to better evaluate the differential glycosylation patterns between IgG1 antibodies following vaccination.

Understanding the role of antibody glycosylation through the lens of severe viral and bacterial diseases

Abundant evidence points to a critical role for antibodies in protection and pathology across infectious diseases. While the antibody variable domain facilitates antibody binding and the blockade of infection, the constant domain (Fc) mediates cross talk with the innate immune system. The biological activity of the Fc region is controlled genetically via class switch recombination, resulting in the selection of distinct antibody isotypes and subclasses. However, a second modification is made to all antibodies, via post-translational changes in antibody glycosylation. Studies from autoimmunity and oncology have established the role of immunoglobulin G (IgG) Fc glycosylation as a key regulator of humoral immune activity. However, a growing body of literature, exploring IgG Fc glycosylation through the lens of infectious diseases, points to the role of inflammation in shaping Fc-glycan profiles, the remarkable immune plasticity in antibody glycosylation across pathogen-exposed populations, the canonical and noncanonical functions of glycans and the existence of antigen-specific control over antibody Fc glycosylation. Ultimately, this work provides critical new insights into the functional roles for antibody glycosylation as well as lays the foundation for leveraging antibody glycosylation to drive prevention or control across diseases.

Sialylated Immunoglobulins for the Treatment of Immuno-Inflammatory Diseases

Immunoglobulins are the potent effector proteins of the humoral immune response. In the course of evolution, immunoglobulins have formed extremely diverse types of molecular structures with antigen-recognizing, antigen-binding, and effector functions embedded in a single molecule. Polysaccharide moiety of immunoglobulins plays the essential role in immunoglobulin functioning. There is growing evidence that the carbohydrate composition of immunoglobulin-linked glycans, and especially their terminal sialic acid residues, provide a key effect on the effector functions of immunoglobulins. Possibly, sialylation of Fc glycan is a common mechanism of IgG anti-inflammatory action in vivo. Thus, the post-translational modification (glycosylation) of immunoglobulins opens up significant possibilities in the diagnosis of both immunological and inflammatory disorders and in their therapies. This review is focused on the analysis of glycosylation of immunoglobulins, which can be a promising addition to improve existing strategies for the diagnosis and treatment of various immuno-inflammatory diseases.

Maternal Immunization: Nature Meets Nurture

Vaccinating women in pregnancy (i.e., maternal immunization) has emerged as a promising tool to tackle infant morbidity and mortality worldwide. This approach nurtures a 'gift of nature,' whereby antibody is transferred from mother to fetus transplacentally during pregnancy, or postnatally in breast milk, thereby providing passive, antigen-specific protection against infections in the first few months of life, a period of increased immune vulnerability for the infant. In this review, we briefly summarize the rationale for maternal immunization programs and the landscape of vaccines currently in use or in the pipeline. We then direct the focus to the underlying biological phenomena, including the main mechanisms by which maternally derived antibody is transferred efficiently to the infant, at the placental interface or in breast milk; important research models and methodological approaches to interrogate these processes, particularly in the context of recent advances in systems vaccinology; the potential biological and clinical impact of high maternal antibody titres on neonatal ontogeny and subsequent infant vaccine responses; and key vaccine- and host-related factors influencing the maternal-infant dyad across different environments. Finally, we outline important gaps in knowledge and suggest future avenues of research on this topic, proposing potential strategies to ensure optimal testing, delivery and implementation of maternal vaccination programs worldwide.

Fc Glycan-Mediated Regulation of Placental Antibody Transfer

Despite the worldwide success of vaccination, newborns remain vulnerable to infections. While neonatal vaccination has been hampered by maternal antibody-mediated dampening of immune responses, enhanced regulatory and tolerogenic mechanisms, and immune system immaturity, maternal pre-natal immunization aims to boost neonatal immunity via antibody transfer to the fetus. However, emerging data suggest that antibodies are not transferred equally across the placenta. To understand this, we used systems serology to define Fc features associated with antibody transfer. The Fc-profile of neonatal and maternal antibodies differed, skewed toward natural killer (NK) cell-activating antibodies. This selective transfer was linked to digalactosylated Fc-glycans that selectively bind FcRn and FCGR3A, resulting in transfer of antibodies able to efficiently leverage innate immune cells present at birth. Given emerging data that vaccination may direct antibody glycosylation, our study provides insights for the development of next-generation maternal vaccines designed to elicit antibodies that will most effectively aid neonates.

Response to immune complex vaccine in chronic hepatitis B patients is associated with lower baseline level of serum IgG galactosylation

The composition of glycan in immunoglobulin G (IgG) has shown to affect various diseases and can be regulated by drugs and preventive vaccination. A hepatitis B surface antigen (HBsAg)-hepatitis B immunoglobulin (HBIG) immune complex (YIC) therapeutic vaccine for chronic hepatitis B (CHB) patients has undergone clinical trials. To explore for markers of CHB, which could be associated with responsiveness to YIC therapeutic vaccine, serum IgG glycosylation in CHB patients was analyzed.Kinetic changes of serum galactosylated IgG in 53 hepatitis Be antigen (HBeAg)-positive CHB patients treated with YIC were monitored by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) analysis. Whole blood cytokines were assayed by cytokine binding assay kits. All samples were back assayed before treatment, during therapy and follow-up for 6 months from a previous completed clinical trial.During YIC treatment, 26 patients with lower IgG galactosylation level at baseline [galactosylation level (Gal-ratio) = -0.29, 0.18 (mean, SD)] showed sustained increase of serum galactosylated IgG, and responded to YIC treatment by HBeAg seroconversion. While those who did not respond to YIC treatment [Gal-ratio = -0.40, 0.15 (mean, SD)] failed to show similar changes. Furthermore, this kinetic increase of galactosylated IgG correlated with marked up-regulated IL-2 level, confirming that effective cellular immune responses have participated in responsiveness.For HBeAg-positive CHB patients lower serum IgG galactosylation level may serve as an indicator for selecting a suitable subpopulation of candidates for YIC therapeutic vaccination.

Antibody glycosylation in inflammation, disease and vaccination

Antibodies are antigen recognizing immunoglobulins with an amazingly diverse repertoire in the antigen specific domain. The diversity of the antibody response is further increased by modifications such as somatic recombination and hypermutation. Furthermore, variation in the isotype and post-translational modifications such as Fc glycosylation further increase diversity of the effector functions. In particular variations in the glycan structures contribute significantly to the functional capacities of the antibodies. This is of particular interest given the dynamic nature of these modifications that is strongly influenced by the inflammatory environment.

Intriguingly, the glycan profile of antibodies has been unravelled in great detail in inflammatory (auto)immune diseases but received only limited attention in the area of infectious diseases and vaccination. Here, we reviewed the current knowledge on immunoglobulin glycosylation and specifically focussed on studies in the field of infectious diseases and vaccination against infectious diseases, an area with a lot of interesting opportunities.

Differences in IgG Fc Glycosylation Are Associated with Outcome of Pediatric Meningococcal Sepsis

Pediatric meningococcal sepsis often results in morbidity and/or death, especially in young children. Our understanding of the reasons why young children are more susceptible to both the meningococcal infection itself and a more fulminant course of the disease is limited. Immunoglobulin G (IgG) is involved in the adaptive immune response against meningococcal infections, and its effector functions are highly influenced by the glycan structure attached to the fragment crystallizable (Fc) region. It was hypothesized that IgG Fc glycosylation might be related to the susceptibility and severity of meningococcal sepsis. Because of this, the differences in IgG Fc glycosylation between 60 pediatric meningococcal sepsis patients admitted to the pediatric intensive care unit and 46 age-matched healthy controls were investigated, employing liquid chromatography with mass spectrometric detection of tryptic IgG glycopeptides. In addition, Fc glycosylation profiles were compared between patients with a severe outcome (death or the need for amputation) and a nonsevere outcome. Meningococcal sepsis patients under the age of 4 years showed lower IgG1 fucosylation and higher IgG1 bisection than age-matched healthy controls. This might be a direct effect of the disease; however, it can also be a reflection of previous immunologic challenges and/or a higher susceptibility of these children to develop meningococcal sepsis. Within the young patient group, levels of IgG1 hybrid-type glycans and IgG2/3 sialylation per galactose were associated with illness severity and severe outcome. Future studies in larger groups should explore whether IgG Fc glycosylation could be a reliable predictor for meningococcal sepsis outcome.

Meningococcal sepsis causes significant mortality and morbidity worldwide, especially in young children. Identification of risk factors for a more fulminant infection would help to decide on appropriate treatment strategies for the individual patients. Immunoglobulin G (IgG) plays an essential role in humoral immune responses and is involved in the adaptive immune response against meningococcal infections. Of great influence on the receptor affinity of IgG is the N-glycan on its fragment crystallizable (Fc) portion. In the present study, we analyzed IgG glycosylation during the fast development of meningococcal sepsis in children, and we were able to identify glycosylation features that are different between meningococcal sepsis patients and healthy controls. These features might be indicative of a higher susceptibility to meningococcal sepsis. In addition, we found glycosylation features in the patients that were associated with illness severity and severe disease outcome, having the potential to serve as a disease outcome predictor.

Fc-Glycosylation in Human IgG1 and IgG3 Is Similar for Both Total and Anti-Red-Blood Cell Anti-K Antibodies

After albumin, immunoglobulin G (IgG) are the most abundant proteins in human serum, with IgG1 and IgG3 being the most abundant subclasses directed against protein antigens. The quality of the IgG-Fc-glycosylation has important functional consequences, which have been found to be skewed toward low fucosylation in some antigen-specific immune responses. This increases the affinity to IgG1-Fc-receptor (FcγR)IIIa/b and thereby directly affects downstream effector functions and disease severity. To date, antigen-specific IgG-glycosylation have not been analyzed for IgG3. Here, we analyzed 30 pregnant women with anti-K alloantibodies from a prospective screening cohort and compared the type of Fc-tail glycosylation of total serum- and antigen-specific IgG1 and IgG3 using mass spectrometry. Total serum IgG1 and IgG3 Fc-glycoprofiles were highly similar. Fc glycosylation of antigen-specific IgG varied greatly between individuals, but correlated significantly with each other for IgG1 and IgG3, except for bisection. However, although the magnitude of changes in fucosylation and galactosylation were similar for both subclasses, this was not the case for sialylation levels, which were significantly higher for both total and anti-K IgG3. We found that the combination of relative IgG1 and IgG3 Fc-glycosylation levels did not improve the prediction of anti-K mediated disease over IgG1 alone. In conclusion, Fc-glycosylation profiles of serum- and antigen-specific IgG1 and IgG3 are highly similar.

Antigen specificity determines anti-red blood cell IgG-Fc alloantibody glycosylation and thereby severity of haemolytic disease of the fetus and newborn

Haemolytic disease of the fetus and newborn (HDFN) is a severe disease in which fetal red blood cells (RBC) are destroyed by maternal anti-RBC IgG alloantibodies. HDFN is most often caused by anti-D but may also occur due to anti-K, -c- or -E. We recently found N-linked glycosylation of anti-D to be skewed towards low fucosylation, thereby increasing the affinity to IgG-Fc receptor IIIa and IIIb, which correlated with HDFN disease severity. Here, we analysed 230 pregnant women with anti-c, -E or -K alloantibodies from a prospective screening cohort and investigated the type of Fc-tail glycosylation of these antibodies in relation to the trigger of immunisation and pregnancy outcome. Anti-c, -E and -K show - independent of the event that had led to immunisation - a different kind of Fc-glycosylation compared to that of the total IgG fraction, but with less pronounced differences compared to anti-D. High Fc-galactosylation and sialylation of anti-c correlated with HDFN disease severity, while low anti-K Fc-fucosylation correlated with severe fetal anaemia. IgG-Fc glycosylation of anti-RBC antibodies is shaped depending on the antigen. These features influence their clinical potency and may therefore be used to predict severity and identify those needing treatment.

A Functional Role for Antibodies in Tuberculosis

While a third of the world carries the burden of tuberculosis, disease control has been hindered by a lack of tools, including a rapid, point-of-care diagnostic and a protective vaccine. In many infectious diseases, antibodies (Abs) are powerful biomarkers and important immune mediators. However, in Mycobacterium tuberculosis (Mtb) infection, a discriminatory or protective role for humoral immunity remains unclear. Using an unbiased antibody profiling approach, we show that individuals with latent tuberculosis infection (Ltb) and active tuberculosis disease (Atb) have distinct Mtb-specific humoral responses, such that Ltb infection is associated with unique Ab Fc functional profiles, selective binding to FcγRIII, and distinct Ab glycosylation patterns. Moreover, compared to Abs from Atb, Abs from Ltb drove enhanced phagolysosomal maturation, inflammasome activation, and, most importantly, macrophage killing of intracellular Mtb. Combined, these data point to a potential role for Fc-mediated Ab effector functions, tuned via differential glycosylation, in Mtb control.

Glycosylation pattern of anti-platelet IgG is stable during pregnancy and predicts clinical outcome in alloimmune thrombocytopenia

Fetal or neonatal alloimmune thrombocytopenia (FNAIT) is a potentially life-threatening disease where fetal platelets are destroyed by maternal anti-platelet IgG alloantibodies. The clinical outcome varies from asymptomatic, to petechiae or intracranial haemorrhage, but no marker has shown reliable correlation with severity, making screening for FNAIT impractical and highly inefficient. We recently found IgG Fc-glycosylation towards platelet and red blood cell antigens to be skewed towards decreased fucosylation, increased galactosylation and sialylation. The lowered core-fucosylation increases the affinity of the pathogenic antibodies to FcγRIIIa and FcγRIIIb, and hence platelet destruction. Here we analysed the N-linked glycans of human platelet antigen (HPA)-1a specific IgG1 with mass spectrometry in large series of FNAIT cases (n = 166) including longitudinal samples (n = 26). Besides a significant decrease in Fc-fucosylation after the first pregnancy (P = 0·0124), Fc-glycosylation levels remained stable during and after pregnancy and in subsequent pregnancies. Multiple logistic regression analysis identified anti-HPA-1a -fucosylation (P = 0·006) combined with galactosylation (P = 0·021) and antibody level (P = 0·038) correlated with bleeding severity, making these parameters a feasible marker in screening for severe cases of FNAIT.

Influence of Glycosylation Inhibition on the Binding of KIR3DL1 to HLA-B*57:01

Viral infections can affect the glycosylation pattern of glycoproteins involved in antiviral immunity. Given the importance of protein glycosylation for immune function, we investigated the effect that modulation of the highly conserved HLA class I N-glycan has on KIR:HLA interactions and NK cell function. We focused on HLA-B*57:01 and its interaction with KIR3DL1, which has been shown to play a critical role in determining the progression of a number of human diseases, including human immunodeficiency virus-1 infection. 721.221 cells stably expressing HLA-B*57:01 were treated with a panel of glycosylation enzyme inhibitors, and HLA class I expression and KIR3DL1 binding was quantified. In addition, the functional outcomes of HLA-B*57:01 N-glycan disruption/modulation on KIR3DL1ζ+ Jurkat reporter cells and primary human KIR3DL1+ NK cells was assessed. Different glycosylation enzyme inhibitors had varying effects on HLA-B*57:01 expression and KIR3DL1-Fc binding. The most remarkable effect was that of tunicamycin, an inhibitor of the first step of N-glycosylation, which resulted in significantly reduced KIR3DL1-Fc binding despite sustained expression of HLA-B*57:01 on 721.221 cells. This effect was paralleled by decreased activation of KIR3DL1ζ+ Jurkat reporter cells, as well as increased degranulation of primary human KIR3DL1+ NK cell clones when encountering HLA-B*57:01-expressing 721.221 cells that were pre-treated with tunicamycin. Overall, these results demonstrate that N-glycosylation of HLA class I is important for KIR:HLA binding and has an impact on NK cell function.