In Vitro Enhancement of Respiratory Syncytial Virus Infection by Maternal Antibodies Does Not Explain Disease Severity in Infants.

Respiratory syncytial virus (RSV) is the leading cause of severe respiratory illness in infants. At this young age, infants typically depend on maternally transferred antibodies (matAbs) and their innate immune system for protection against infections. RSV-specific matAbs are thought to protect from severe illness, yet severe RSV disease occurs mainly below 6 months of age, when neutralizing matAb levels are present. To investigate this discrepancy, we asked if disease severity is related to antibody properties other than neutralization. Some antibody effector functions are mediated via their Fc binding region. However, it has been shown that this binding may lead to antibody-dependent enhancement (ADE) of infection or reduction of neutralization, both possibly leading to more disease. In this study, we first showed that high levels of ADE of RSV infection occur in monocytic THP-1 cells in the presence of RSV antibodies and that neutralization by these antibodies was reduced in Vero cells when they were transduced with Fc gamma receptors. We then demonstrated that antibodies from cotton rats with formalin-inactivated (FI)-RSV-induced pulmonary pathology were capable of causing ADE. Human matAbs also caused ADE and were less neutralizing in vitro in cells that carry Fc receptors. However, these effects were unrelated to disease severity because they were seen both in uninfected controls and in infants hospitalized with different levels of RSV disease severity. We conclude that ADE and reduction of neutralization are unlikely to be involved in RSV disease in infants with neutralizing matAbs.IMPORTANCE It is unclear why severity of RSV disease peaks at the age when infants have neutralizing levels of maternal antibodies. Additionally, the exact reason for FI-RSV-induced enhanced disease, as seen in the 1960s vaccine trials, is still unclear. We hypothesized that antibodies present under either of these conditions could contribute to disease severity. Antibodies can have effects that may lead to more disease instead of protection. We investigated two of those effects: antibody-dependent enhancement of infection (ADE) and neutralization reduction. We show that ADE occurs in vitro with antibodies from FI-RSV-immunized RSV-infected cotton rats. Moreover, passively acquired maternal antibodies from infants had the capacity to induce ADE and reduction of neutralization. However, no clear association with disease severity was seen, ruling out that these properties explain disease in the presence of maternal antibodies. Our data contribute to a better understanding of the impact of antibodies on RSV disease in infants

Siglec-1 inhibits RSV-induced interferon gamma production by adult T cells in contrast to newborn T cells.

Interferon gamma (IFN-γ) plays an important role in the antiviral immune response during respiratory syncytial virus (RSV) infections. Monocytes and T cells are recruited to the site of RSV infection, but it is unclear whether cell-cell interactions between monocytes and T cells regulate IFN-γ production. In this study, micro-array data identified the upregulation of sialic acid-binding immunoglobulin-type lectin 1 (Siglec-1) in human RSV-infected infants. In vitro, RSV increased expression of Siglec-1 on healthy newborn and adult monocytes. RSV-induced Siglec-1 on monocytes inhibited IFN-γ production by adult CD4+T cells. In contrast, IFN-γ production by RSV in newborns was not affected by Siglec-1. The ligand for Siglec-1, CD43, is highly expressed on adult CD4+T cells compared to newborns. Our data show that Siglec-1 reduces IFN-γ release by adult T cells possibly by binding to the highly expressed CD43. The Siglec-1-dependent inhibition of IFN-γ in adults and the low expression of CD43 on newborn T cells provides a better understanding of the immune response against RSV in early life and adulthood

Siglec-1 inhibits RSV-induced interferon gamma production by adult T cells in contrast to newborn T cells.

Interferon gamma (IFN-γ) plays an important role in the antiviral immune response during respiratory syncytial virus (RSV) infections. Monocytes and T cells are recruited to the site of RSV infection, but it is unclear whether cell-cell interactions between monocytes and T cells regulate IFN-γ production. In this study, micro-array data identified the upregulation of sialic acid-binding immunoglobulin-type lectin 1 (Siglec-1) in human RSV-infected infants. In vitro, RSV increased expression of Siglec-1 on healthy newborn and adult monocytes. RSV-induced Siglec-1 on monocytes inhibited IFN-γ production by adult CD4+T cells. In contrast, IFN-γ production by RSV in newborns was not affected by Siglec-1. The ligand for Siglec-1, CD43, is highly expressed on adult CD4+T cells compared to newborns. Our data show that Siglec-1 reduces IFN-γ release by adult T cells possibly by binding to the highly expressed CD43. The Siglec-1-dependent inhibition of IFN-γ in adults and the low expression of CD43 on newborn T cells provides a better understanding of the immune response against RSV in early life and adulthood

In vitro enhancement of RSV infection by maternal antibodies does not explain disease severity in infants

Respiratory syncytial virus (RSV) is the leading cause of severe respiratory illness in infants. At this young age, infants typically depend on maternally transferred antibodies (matAbs) and their innate immune system for protection against infections. RSV-specific matAbs are thought to protect from severe illness, yet severe RSV disease occurs mainly below 6 months of age, when neutralizing matAb levels are present. To investigate this discrepancy, we asked if disease severity is related to antibody properties other than neutralization. Some antibody effector functions are mediated via their Fc binding region. However, it has been shown that this binding may lead to antibody-dependent enhancement (ADE) of infection or reduction of neutralization, both possibly leading to more disease. In this study, we first showed that high levels of ADE of RSV infection occur in monocytic THP-1 cells in the presence of RSV antibodies and that neutralization by these antibodies was reduced in Vero cells when they were transduced with Fc gamma receptors. We then demonstrated that antibodies from cotton rats with formalin-inactivated- (FI-) RSV-induced pulmonary pathology were capable of causing ADE. Human matAbs also caused ADE and were less neutralizing in vitro in cells that carry Fc receptors. However, these effects were unrelated to disease severity because they were seen both in uninfected controls and in infants hospitalized with different levels of RSV disease severity. We conclude that ADE and reduction of neutralization are unlikely to be involved in RSV disease in infants with neutralizing matAbs.IMPORTANCE It is unclear why severity of RSV disease peaks at the age when infants have neutralizing levels of maternal antibodies. Additionally, the exact reason for FI-RSV-induced enhanced disease, as seen in the 1960's vaccine trials, is still unclear. We hypothesized that antibodies present in either of these conditions could contribute to disease severity. Antibodies can have effects that may lead to more disease instead of protection. We investigated two of those effects: antibody-dependent enhancement of infection (ADE) and neutralization reduction. We show that ADE occurs in vitro with antibodies from FI-RSV-immunized RSV-infected cotton rats. Moreover, passively acquired maternal antibodies from infants had the capacity to induce ADE and reduction of neutralization. However, no clear association with disease severity was seen, ruling out that these properties explain disease in the presence of maternal antibodies. Our data contribute to a better understanding of the impact of antibodies on RSV disease in infants

Characteristics of RSV-Specific Maternal Antibodies in Plasma of Hospitalized, Acute RSV Patients under Three Months of Age.

Respiratory syncytial virus (RSV) is the leading cause for respiratory illness that requires hospitalization in infancy. High levels of maternal antibodies can protect against RSV infection. However, RSV-infected infants can suffer from severe disease symptoms even in the presence of high levels of RSV-specific antibodies. This study analyzes several serological characteristics to explore potential deficiencies or surpluses of antibodies that could relate to severe disease symptoms. We compare serum antibodies from hospitalized patients who suffered severe symptoms as well as uninfected infants. Disease severity markers were oxygen therapy, tachypnea, oxygen saturation, admission to the intensive care unit and duration of hospitalization. Antibodies against RSV G protein and a prefusion F epitope correlated with in vitro neutralization. Avidity of RSV-specific IgG antibodies was lower in RSV-infected infants compared to uninfected controls. Severe disease symptoms were unrelated to RSV-specific IgG antibody titers, avidity of RSV-IgG, virus neutralization capacity or titers against pre- and postfusion F or G protein ectodomains and the prefusion F antigenic site Ø. In conclusion, the detailed serological characterization did not indicate dysfunctional or epitope-skewed composition of serum antibodies in hospitalized RSV-infected infants suffering from severe disease symptoms. It remains unclear, whether specific antibody fractions could diminish disease symptoms

Natural killer cell activation by respiratory syncytial virus-specific antibodies is decreased in infants with severe respiratory infections and correlates with Fc-glycosylation

Objectives: Respiratory syncytial virus (RSV) is a major cause of severe lower respiratory tract infections in infants, and there is no vaccine available. In early life, the most important contributors to protection against infectious diseases are the innate immune response and maternal antibodies. However, antibody-mediated protection against RSV disease is incompletely understood, as both antibody levels and neutralisation capacity correlate poorly with protection. Since antibodies also mediate natural killer (NK) cell activation, we investigated whether this functionality correlates with RSV disease. Methods: We performed an observational case-control study including infants hospitalised for RSV infection, hernia surgery or RSV-negative respiratory viral infections. We determined RSV antigen-specific antibody levels in plasma using a multiplex immunoassay. Subsequently, we measured the capacity of these antibodies to activate NK cells. Finally, we assessed Fc-glycosylation of the RSV-specific antibodies by mass spectrometry. Results: We found that RSV-specific maternal antibodies activate NK cells in vitro. While concentrations of RSV-specific antibodies did not differ between cases and controls, antibodies from infants hospitalised for severe respiratory infections (RSV and/or other) induced significantly less NK cell interferon-γ production than those from uninfected controls. Furthermore, NK cell activation correlated with Fc-fucosylation of RSV-specific antibodies, but their glycosylation status did not significantly differ between cases and controls. Conclusion: Our results suggest that Fc-dependent antibody function and quality, exemplified by NK cell activation and glycosylation, contribute to protection against severe RSV disease and warrant further studies to evaluate the potential of using these properties to evaluate and improve the efficacy of novel vaccines

RSV-specific IgG against prefusion F epitope and G protein correlate with neutralization.

<p>Neutralization titers against RSV-X (PRNT) were compared to IgG levels against (A) postfusion F protein, (B) site I (131-2A competition titer), (C) prefusion F protein, (D) site Ø (D25 competition titer) and (E) G protein. Testing for correlation was performed with Spearman correlation test.</p