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

Fc galactosylation of anti-platelet human IgG1 alloantibodies enhances complement activation on platelets

Approximately 20% of patients receiving multiple platelet transfusions develop platelet alloantibodies, which can be directed against human leukocyte antigens (HLA) and, to a lesser extent, against human platelet antigens (HPA). These antibodies can lead to the rapid clearance of donor platelets, presumably through IgG-Fc receptor (FcγR)-mediated phagocytosis or via complement activation, resulting in platelet refractoriness. Strikingly, not all patients with anti-HLA or -HPA antibodies develop platelet refractoriness upon unmatched platelet transfusions. Previously, we found that IgG Fc glycosylation of anti-HLA antibodies was highly variable between patients with platelet refractoriness, especially with respect to galactosylation and sialylation of the Fc-bound sugar moiety. Here, we produced recombinant glycoengineered anti-HLA and anti- HPA-1a monoclonal antibodies with varying Fc galactosylation and sialylation levels and studied their ability to activate the classical complement pathway. We observed that anti-HLA monoclonal antibodies with different specificities, binding simultaneously to the same HLA-molecules, or anti-HLA in combination with anti-HPA-1a monoclonal antibodies interacted synergistically with C1q, the first component of the classical pathway. Elevated Fc galactosylation and, to a lesser extent, sialylation significantly increased the complement-activating properties of anti-HLA and anti-HPA-1a monoclonal antibodies. We propose that both the breadth of the polyclonal immune response, with recognition of different HLA epitopes and in some cases HPA antigens, and the type of Fc glycosylation can provide an optimal stoichiometry for C1q binding and subsequent complement activation. These factors can shift the effect of a platelet alloimmune response to a clinically relevant response, leading to complement-mediated clearance of donor platelets, as observed in platelet refractoriness

Unique patterns of glycosylation in immunoglobulin subclass G4‐related disease and primary sclerosing cholangitis

Background: Immunoglobulin subclass G4‐related disease (IgG4‐RD) is characterized by an abundance of IgG4 antibodies in the serum and tissue. Glycosylation status of antibodies can impact on immune effector functions and disease pathophysiology. We sought to establish glycosylation patterns in a prospective cohort of patients with IgG4‐RD and the relationship with disease activity and response to treatment. Methods: We assessed IgG Fc‐tail and Fab‐arm glycosylation status in patients with IgG4‐RD (n = 22), disease controls with primary sclerosing cholangitis (PSC) (n = 22), and healthy controls (n = 22). Serum IgG and subclasses were quantified using ELISA. Fc and Fab glycosylation were analyzed by mass spectrometry and lectin affinity chromatography, respectively. Disease activity, organ damage, and response to treatment were assessed using the IgG4 Responder Index. Results: Immunoglobulin G Fab sialylation was increased in IgG4‐RD compared with PSC and healthy control (P = 0.01), with a preferential increase in IgG4‐specific Fab sialylation, which was independent of IgG4 Fab‐arm exchange. There was a reduction in IgG1‐specific Fc bisection and hybrid structures in IgG4‐RD (P &lt; 0.01), which recovered upon steroid treatment and correlated with disease activity. Overall, IgG Fc galactosylation was reduced in both IgG4‐RD and PSC (P &lt; 0.01), with a preferential reduction in IgG1‐specific sialylation and enhancement of IgG4‐specific bisection in PSC. IgG4 fucosylation and IgG1/2/3 hybrid structures negatively correlated with complement C3 and C4 levels in IgG4‐RD (P &lt; 0.01), but not PSC. Conclusion: We report the first study showing unique antibody glycosylation status in a prospective cohort of IgG4‐RD and PSC patients, which may determine modulation of the immune system and contribute to disease pathophysiology.</p

Unique patterns of glycosylation in immunoglobulin subclass G4‐related disease and primary sclerosing cholangitis

Background: Immunoglobulin subclass G4‐related disease (IgG4‐RD) is characterized by an abundance of IgG4 antibodies in the serum and tissue. Glycosylation status of antibodies can impact on immune effector functions and disease pathophysiology. We sought to establish glycosylation patterns in a prospective cohort of patients with IgG4‐RD and the relationship with disease activity and response to treatment. Methods: We assessed IgG Fc‐tail and Fab‐arm glycosylation status in patients with IgG4‐RD (n = 22), disease controls with primary sclerosing cholangitis (PSC) (n = 22), and healthy controls (n = 22). Serum IgG and subclasses were quantified using ELISA. Fc and Fab glycosylation were analyzed by mass spectrometry and lectin affinity chromatography, respectively. Disease activity, organ damage, and response to treatment were assessed using the IgG4 Responder Index. Results: Immunoglobulin G Fab sialylation was increased in IgG4‐RD compared with PSC and healthy control (P = 0.01), with a preferential increase in IgG4‐specific Fab sialylation, which was independent of IgG4 Fab‐arm exchange. There was a reduction in IgG1‐specific Fc bisection and hybrid structures in IgG4‐RD (P Conclusion: We report the first study showing unique antibody glycosylation status in a prospective cohort of IgG4‐RD and PSC patients, which may determine modulation of the immune system and contribute to disease pathophysiology.</p

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

Distinct glycosylation and functional profile of typhoid vaccine-induced antibodies in a UK challenge study and Nepalese children

Vaccines against typhoid fever have been shown to be safe and effective in field trials. The mechanism through which the vaccines protect remains elusive. Recent data have implicated antibody glycosylation, and specifically afucosylated antibodies, as an important factor in vaccine-induced effector function for a range of viral infections, however this has not been evaluated for vaccines against bacterial infections such as Salmonella typhi. Here, we studied antibody glycosylation after either Vi-conjugate or Vi-polysaccharide vaccine in a UK cohort who were then challenged with virulent S. typhi, and compared findings to antibody glycosylation after Vi-conjugate vaccine in Nepalese children living in a typhoid endemic region. We compared vaccine-induced responses and correlated these measures with antibody-dependent function. Robust antigen-specific antibody galactosylation and sialylation modifications were induced by both vaccines in UK adults, with Vi-conjugate vaccine inducing Vi-specific glycan changes of higher magnitude than Vi-polysaccharide. Among those individuals diagnosed with typhoid fever after challenge, a distinct glycan profile was correlated with disease severity. Elevated galactosylation and sialylation was correlated with increased antibody-dependent phagocytosis by macrophages and neutrophils among UK adults. While bulk IgG glycosylation differed between Nepalese children and UK adults, vaccination with the Vi-conjugate vaccine overcame these differences to result in similar Vi-specific antibody glycosylation profiles 28 days after vaccination in both cohorts

Fc galactosylation of anti-platelet human IgG1 alloantibodies enhances complement activation on platelets

Approximately 20% of patients receiving multiple platelet transfusions develop platelet alloantibodies, which can be directed against human leukocyte antigens (HLA) and, to a lesser extent, against human platelet antigens (HPA). These antibodies can lead to the rapid clearance of donor platelets, presumably through IgG-Fc receptor (FcγR)-mediated phagocytosis or via complement activation, resulting in platelet refractoriness. Strikingly, not all patients with anti-HLA or -HPA antibodies develop platelet refractoriness upon unmatched platelet transfusions. Previously, we found that IgG Fc glycosylation of anti-HLA antibodies was highly variable between patients with platelet refractoriness, especially with respect to galactosylation and sialylation of the Fc-bound sugar moiety. Here, we produced recombinant glycoengineered anti-HLA and anti- HPA-1a monoclonal antibodies with varying Fc galactosylation and sialylation levels and studied their ability to activate the classical complement pathway. We observed that anti-HLA monoclonal antibodies with different specificities, binding simultaneously to the same HLA-molecules, or anti-HLA in combination with anti-HPA-1a monoclonal antibodies interacted synergistically with C1q, the first component of the classical pathway. Elevated Fc galactosylation and, to a lesser extent, sialylation significantly increased the complement-activating properties of anti-HLA and anti-HPA-1a monoclonal antibodies. We propose that both the breadth of the polyclonal immune response, with recognition of different HLA epitopes and in some cases HPA antigens, and the type of Fc glycosylation can provide an optimal stoichiometry for C1q binding and subsequent complement activation. These factors can shift the effect of a platelet alloimmune response to a clinically relevant response, leading to complement-mediated clearance of donor platelets, as observed in platelet refractoriness

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