Comparison of class and subclass antibody response to live and UV-inactivated RSV administered intranasally in mice

Fc-Mediated Antibody Effector Functions During Respiratory Syncytial Virus Infection and Disease

Respiratory syncytial virus (RSV) is a major cause of severe lower respiratory tract infections and hospitalization in infants under 1 year of age and there is currently no market-approved vaccine available. For protection against infection, young children mainly depend on their innate immune system and maternal antibodies. Traditionally, antibody-mediated protection against viral infections is thought to be mediated by direct binding of antibodies to viral particles, resulting in virus neutralization. However, in the case of RSV, virus neutralization titers do not provide an adequate correlate of protection. The current lack of understanding of the mechanisms by which antibodies can protect against RSV infection and disease or, alternatively, contribute to disease severity, hampers the design of safe and effective vaccines against this virus. Importantly, neutralization is only one of many mechanisms by which antibodies can interfere with viral infection. Antibodies consist of two structural regions: a variable fragment (Fab) that mediates antigen binding and a constant fragment (Fc) that mediates downstream effector functions via its interaction with Fc-receptors on (innate) immune cells or with C1q, the recognition molecule of the complement system. The interaction with Fc-receptors can lead to killing of virus-infected cells through a variety of immune effector mechanisms, including antibody-dependent cell-mediated cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP). Antibody-mediated complement activation may lead to complement-dependent cytotoxicity (CDC). In addition, both Fc-receptor interactions and complement activation can exert a broad range of immunomodulatory functions. Recent studies have emphasized the importance of Fc-mediated antibody effector functions in both protection and pathogenesis for various infectious agents. In this review article, we aim to provide a comprehensive overview of the current knowledge on Fc-mediated antibody effector functions in the context of RSV infection, discuss their potential role in establishing the balance between protection and pathogenesis, and point out important gaps in our understanding of these processes. Furthermore, we elaborate on the regulation of these effector functions on both the cellular and humoral side. Finally, we discuss the implications of Fc-mediated antibody effector functions for the rational design of safe and effective vaccines and monoclonal antibody therapies against RSV.

Enhanced virulence, airway inflammation and impaired lung function induced by respiratory syncytial virus deficient in secreted G protein

BACKGROUND

Respiratory syncytial virus (RSV) infection can cause bronchial hyperresponsiveness and asthma exacerbations. In mice it results in airway inflammation and airway hyperresponsiveness. Since viral factors influencing these responses are not well defined, a study was undertaken to investigate the role of secreted G protein of human RSV in determining virulence, inflammatory responses, and changes in lung function.

METHODS

BALB/c mice were infected with a spontaneous mutant of RSV deficient in secreted G protein (RSV-DeltasG) or with wild type RSV (RSV-WT). Viral titres, numbers of pulmonary inflammatory cells, and concentrations of interferon (IFN)-gamma, interleukin (IL)-4, IL-5 and IL-10 in bronchoalveolar lavage (BAL) fluid were determined. Airway function was assessed at baseline and following methacholine provocation using barometric whole body plethysmography.

RESULT

Following infection with RSV-DeltasG, viral titres were increased 50-fold compared with RSV-WT. Influx of eosinophils and macrophages to the lung and concentrations of IFN-gamma and IL-10 in BAL fluid were also significantly higher following infection with RSV-DeltasG. Airway function, both at baseline and after methacholine provocation, was significantly decreased following infection with RSV-DeltasG compared with RSV-WT.

CONCLUSION

Secreted G protein is likely to be a regulatory factor in RSV infection limiting infectivity of the virus, inflammatory responses in the lungs, and reduction in lung function.

Latency and persistence of respiratory syncytial virus despite T cell immunity

Respiratory syncytial virus (RSV) causes bronchiolitis in infants, which is associated with recurrent wheezing in later childhood. There is mounting evidence that the virus becomes latent or persists in vivo, but little is known about the mechanisms of its latency, persistence, and immune evasion. We therefore infected BALB/c mice intranasally with human RSV, analyzed sequential tissue samples by direct culture and polymerase chain reaction for viral and messenger RNA, and monitored antiviral immune responses. Virus could not be detected in bronchoalveolar lavage samples beyond Day 14, but viral genomic and messenger RNA was present in lung homogenates for 100 days or more; combined depletion of CD4 and CD8 T cells allowed infective virus to be recovered. Neutralizing antibody and memory cytotoxic T cell responses were intact in mice with latent infections, and latent viral genome contained an authentic nonmutated M2 82-91 K(d) cytotoxic T lymphocyte epitope. A mutation of this epitope, detected in one clone, did not assist evasion. We suggest that RSV latency depends on persistence in privileged sites rather than on viral mutation.

Respiratory syncytial virus infection results in airway hyperresponsiveness and enhanced airway sensitization to allergen

Viral respiratory infections can predispose to the development of asthma by mechanisms that are presently undetermined. Using a murine model of respiratory syncytial virus (RSV) infection, acute infection is associated with airway hyperresponsiveness as well as enhanced responses to subsequent sensitization to allergen. We demonstrate that acute viral infection results in increased airway responsiveness to inhaled methacholine and pulmonary neutrophilic and eosinophilic inflammation. This response is associated with predominant production of Th-1-type cytokines in peribronchial lymph node cells in vitro. Mice sensitized to ovalbumin via the airways after RSV infection developed increased airway responsiveness to methacholine and pulmonary eosinophilic and neutrophilic inflammation, associated with the predominant production of Th-2-type cytokines. Treatment of the mice with anti-IL-5 antibody abolished airway hyperresponsiveness and eosinophilic but not neutrophilic inflammation in both acutely infected mice and mice sensitized after infection. We conclude that RSV infection results in airway hyperresponsiveness in the acute phase and leads to changes in immune function that can enhance the effects of airway sensitization to antigen after infection. In both situations, airway hyperresponsiveness is closely associated with pulmonary eosinophilic inflammation. This model provides a means for further analyzing the influence of viral respiratory infections on airway sensitization and the development of altered airway responsiveness.

Novel intranasal immunization techniques for antibody induction and protection of mice against gastric Helicobacter felis infection

Intranasal (i.n.) delivery of antigen can be highly effective for generating circulating and secretory antibody responses. Mice were immunized i.n. with two antigens, human IgA, and Helicobacter pylori urease in the presence or absence of mucosal adjuvant. To restrict antigen delivery to the upper airways, protein solutions were administered in a small volume without anesthesia. Repeated daily i.n. administration of antigen without adjuvant elicited high levels of specific IgG in serum and IgA in serum, saliva, and feces. Once weekly i.n. immunization with co-administration of cholera toxin or Escherichia coli heat-labile toxin as adjuvant elicited somewhat lower levels of antibody to urease. When challenged with Helicobacter felis, only mice immunized with urease in the presence of adjuvant were protected against gastric infection.

Similar subclass antibody responses after intranasal immunization with UV-inactivated RSV mixed with cholera toxin or live RSV

To determine the effect of cholera toxin as a mucosal adjuvant on the class and subclass antibody response to RSV, mice were immunized intranasally with different doses of live RSV or UV-inactivated RSV mixed with cholera toxin. A single 10(6) pfu dose of live RSV and a single 50 micrograms dose of UV-inactivated RSV mixed with cholera toxin produced comparable serum IgG and respiratory secretion IgG and IgA antibody titers. Subclass antibody titers to whole RSV were also comparable between these two immunizing regimens. A predominance of IgG2a subclass to whole RSV was found for both regimens. The quantity of serum total IgG antibody to glycoprotein F or glycoprotein G did not differ between these regimens. The serum IgG subclass antibody response to both glycoprotein F and G was also not significantly different between regimens. Cholera toxin as a mucosal adjuvant can stimulate class and subclass antibody responses to UV-inactivated RSV that are similar in quantity and distribution to those after live RSV infection.