The role of antibodies in human immunity to respiratory syncytial virus infections

Robinson, Bernard Stephen (1990) The role of antibodies in human immunity to respiratory syncytial virus infections. University of Southampton, Doctoral Thesis.

Abstract

Respiratory syncytial (RS) virus is a major pathogen causing winter outbreaks of respiratory infections of particular severity in infants. Antigenic sites and protective epitopes on RS virus fusion protein (F), a potent inducer of protective immunity, have been characterised using monoclonal antibodies. Thirty-one monoclonal antibodies identified as reactive with F by radioimmunoprecipitation and western blotting, were used in competitive binding assays with ¹²⁵I-labelled antibodies. Five antigenic sites on F were recognised. One antibody, F3, reacted with reduced F by western blotting to produce bands corresponding in M_r to the F₁and F₂ subunits. The antiviral properties of monoclonal antibodies reactive to four of the sites (F1, F2, F3 and F4) were determined against strains of both RS virus subtypes. F3 and F4 monoclonal antibodies possessed fusion-inhibiting and neutralising activities, while F1 and F2 on neutralised RS virus when complement was added. All possessed CDCL activity. Inter- and intra-subtype variation was detected in the susceptibility of virus strains to fusion inhibiting, neutralising and CDCL activities of the monoclonal antibodies. Antigenic variation of RS viruses isolated in Southampton during one epidemic at these and other F epitopes was confirmed by immunofluorescence (IF). Competition assays with biotin-labelled monoclonal antibodies verified F1, F2, F3, and F4 bound to separate epitopes. The concentrations of antibodies specifically reactive with these four epitopes were measured in 389 prenatal sera by a competition ELISA. Virtually all the sera contained antibodies reactive with each epitope but the concentrations varied. Antibody concentrations to the F3 and F4 epitopes for the population gave normal distributions with narrow ranges which suggest they might be readily boosted by appropriate vaccination. One plausible vaccine is live attenuated RS virus which by nasal replication could induce mucosal and systemic immunity. To date, such vaccines have proved too attenuated, pathogenic or unstable. The antibody responses of adult volunteers to intranasal challenge with wild-type and temperature sensitive (ts) mutants of RS virus were examined in a collaborative study. The relationships between pre-challenge antibody levels and vaccine-induced clinical scores, or virus isolation revealed that both serum and nasal wash neutralising antibodies and IgA to F + G gave the best correlation with protection. Pre-challenge mean nasal wash neutralising antibodies in volunteers having no cold were significantly higher than those with heavy colds (p = 0.001); and the mean neutralising antibody level in individuals shedding virus was about half that of the uninfected group. High levels of serum F3 and F1 epitope reactive antibodies, IgG to F₂ subunit, and IgG to G protein also appeared protective. In contrast serum IgG to whole F and N proteins did not correlate with protection. A clinically attenuated mutant, ts1B, induced comparable antibody responses to wild-type. Ts1B induced higher mean responses than wild-type in the protective serum neutralising, F3 reactive, and IgA to F + G antibodies. Importantly, high responses were produced in some individuals without clinical symptoms and there were no wild-type revertants. Ts1B produced some colds indicating further attenuation of this strain is necessary. RS virus specific IgG concentrations measured in lung washings of fifty adult volunteers were higher and more frequently detectable than IgG reactive with other respiratory viruses. RS virus specific IgG₄/IgG₁ ratios in matching BAL and sera indicated selective uptake or synthesis of RS virus specific IgG₄ in the lung. Locally synthesised IgG may protect the lung against RS virus in co-operation with respiratory-mucosal and serum antibodies.

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