Measurement of antibody against contemporary virus lineages of human respiratory syncytial virus sub-group A in infants and their mothers

Group B streptococcus and respiratory syncytial virus immunisation during pregnancy: a landscape analysis

Group B streptococcus and respiratory syncytial virus are leading causes of infant morbidity and mortality worldwide. No licensed vaccines are available for either disease, but vaccines for both are under development. Severe respiratory syncytial virus disease can be prevented by passively administered antibody. The presence of maternal IgG antibody specific to respiratory syncytial virus is associated with reduced prevalence and severity of respiratory syncytial virus disease in the first few weeks of life, whereas maternal serotype-specific anticapsular antibody is associated with protection against both early-onset and late-onset group B streptococcus disease. Therefore, vaccination in pregnancy might protect infants against both diseases. This report describes what is known about immune protection against group B streptococcus and respiratory syncytial virus, identifies knowledge gaps regarding the immunobiology of both diseases, and aims to prioritise research directions in maternal immunisation.

Generation and epitope mapping of a sub-group cross-reactive anti-respiratory syncytial virus G glycoprotein monoclonal antibody which is protective in vivo

Passively administered antibodies to conserved epitopes on the attachment (G) glycoprotein of human respiratory syncytial virus (hRSV) have potential in the immunoprophylaxis of human infections. This study set out to generate monoclonal antibodies (MAbs) recognizing all prevalent lineages of HRSV and capable of immunoprophylaxis in mice. Two murine MAbs of broad specificity for prevalent virus strains were generated by immunization of mice with hRSV of sub-group A followed by selection of hybridomas on recombinant G glycoprotein from a sub-group B virus. The anti-G hybridomas generated secreted antibody of high affinity but negligible neutralizing capacity one of which was tested in mice and found to be protective against live virus challenge. Western blotting and partial epitope mapping on transiently expressed G-glycoprotein fragments indicate that these antibodies recognize a complex epitope on the protein backbone of the molecule involving residues both C'- and N-terminal to the central conserved motif.

Lower respiratory tract infection caused by respiratory syncytial virus in infants: the role played by specific antibodies

INTRODUCTION

Respiratory syncytial virus (RSV) is a major etiological agent of lower respiratory tract infection in infants. Genotypes of this virus and the role of the infants' serum antibodies have yet to be fully clarified. This knowledge is important for the development of effective therapeutic and prophylactic measures.

OBJECTIVES

To evaluate the types and genotypes of RSV causing respiratory tract infection in infants, to analyze the association of subtype-specific serum antibodies with the occurrence of infection and to evaluate the presence of subtype-specific antibodies in the infants' mothers and their association with the profile of the childrens' serum antibodies.

METHODS

This was a prospective study on infants hospitalized with respiratory infection. Nasopharyngeal secretions were collected for viral investigation using indirect immunofluorescence and viral culture and blood was collected to test for antibodies using the Luminex Multiplex system.

RESULTS

192 infants were evaluated, with 60.9% having RSV (73.5%- A and 20.5% B). Six genotypes of the virus were identified: A5, A2, B3, B5, A7 and B4. The seroprevalence of the subtype-specific serum antibodies was high. The presence and levels of subtype-specific antibodies were similar, irrespective of the presence of infection or the viral type or genotype. The mothers' antibody profiles were similar to their infants'.

CONCLUSIONS

Although the prevalence of subtype-specific antibodies was elevated, these antibodies did not provide protection independently of virus type/genotype. The similarity in the profiles of subtype-specific antibodies presented by the mothers and their children was consistent with transplacental passage.

Early acquisition of herpes simplex virus type 1 antibodies in children—A longitudinal serological study

BACKGROUND

Herpes simplex virus type 1 (HSV-1) infections are commonly acquired in childhood, asymptomatically or as a symptomatic infection. However, little is known about the time of HSV seroconversion during infancy and early childhood.

OBJECTIVE

To investigate the acquisition of IgG-antibodies to HSV in infants and children.

STUDY DESIGN

A longitudinal study, using type-specific HSV-1 and herpes simplex virus type 2 (HSV-2) enzyme-linked immunosorbent assays on sera collected from the mother and from their child at the age of 3, 5, 6, 12, 13 and 30 months.

RESULTS

The maternal seroprevalences for HSV-1 was 65% and for HSV-2 19%. A gradual loss of maternal antibodies was seen, with few infants having detectable HSV-1 antibodies at the age of 1 year. A more rapid decline was registered for HSV-2 antibodies. A small number of new HSV-1 infections occurred in 3-5-month olds and more than half of the new infections were detected before the age of 13 months. At the age of 30 months, 30% of the children were HSV-1 antibody positive.

CONCLUSION

Seroconversion to HSV-1 commonly occurs already during infancy, suggesting that HSV-1 is transmitted primarily from parent to child.

Preparation of a respiratory syncytial virus human reference serum for use in the quantitation of neutralization antibody

Respiratory syncytial virus (RSV) is the major cause of lower respiratory tract infection in infants, young children and the elderly. Yet, the development of a vaccine to protect against RSV infection still remains an unmet need. At present, immune responses to experimental vaccines under investigation are usually evaluated by ELISA and/or by neutralization assays against RSV. However, both types of assays are generally performed somewhat differently at different laboratories. An important step towards standardization of serology is the use of a standard human reference serum enabling normalization of results generated within and between laboratories. To fill this need, we prepared and characterized a human reference serum against the A2 strain of respiratory syncytial virus. The serum represents a pool of more than 400 individual human sera obtained from commercial sources. The sera were screened and selected on the basis of individual RSV neutralization titers. A final neutralization titer of 973 (95% C.I., 884-1072) was assigned to the final reference serum pool after it was tested three times in the presence of 10% guinea pig complement and a titer of 286 (95% C.I., 243-337) was assigned to the serum when it was tested in the absence of an exogenous complement source. Sterilely reconstituted lyophilized aliquots of the serum exhibited a stable neutralization titer for at least 1 month at room temperature and at 4 degrees C, as well as after 5 weekly freeze-and-thaw cycles at -20 degrees C. In the lyophilized state, the neutralization titer of the lyophilized reagent was stable for at least 6 months, the last time point tested. Two additional smaller pools of serum with high and medium neutralization titers of 2692 and 575, respectively, were also produced in parallel for use as positive controls and were designated as control sera. The reference serum can be used to normalize neutralization and/or other RSV-specific assay results from different laboratories and the control sera can be used for quality control purposes or as part of a panel to test operator proficiency. Individual lyophilized aliquots of the reference and control sera may be obtained from the US National Institute of Allergy and Infectious Diseases (NIAID) Reference Reagent Repository.

Increased susceptibility of human respiratory syncytial virus to neutralization by anti-fusion protein antibodies on adaptation to replication in cell culture

Subgroup A respiratory syncytial viruses present in respiratory secretions and low passage level cell culture isolates were found to be markedly less susceptible to neutralization with monoclonal antibodies (MAbs) to the F glycoprotein than the cell culture adapted A2 virus strain. Low passage virus isolates collected over a 20 year period and belonging to several sub-group A lineages were refractory to neutralization with antibodies recognizing two major neutralizing antigenic sites located sub-terminally at opposite ends of the F(1) glycoprotein sub-unit. On further passage in cell culture, virus isolates exhibited both increased infectivity titers and increased susceptibility to neutralization by antibodies to both antigenic sites. The consensus nucleotide sequence of the membrane associated proteins M and of the SH, G and F glycoprotein genes, and their intergenic regions were compared for neutralization resistant and susceptible stocks of one virus strain, R17532. No changes were observed in the known monoclonal antibody epitopes on the F glycoprotein. In line with this, the increase in susceptibility was not found to be associated with any increased binding of monoclonal antibody to isolated F glycoprotein in a BIAcore assay, thus excluding the possibility that passage in cell culture selected for viruses with mutations in the antibody binding sites. M and SH genes were conserved but a number of sites in the G and F glycoprotein genes were found to vary on adaptation to cell culture suggesting that change in susceptibility to neutralization was associated with a change in the prevalent quasispecies present in the virus population. The genetic basis of phenotypic change in susceptibility remains to be determined.

Analysis of the binding of monoclonal and polyclonal antibodies to the glycoproteins of antigenic variants of human respiratory syncytial virus by surface plasmon resonance

The surface glycoproteins of human respiratory syncytial virus (hRSV), F and G, are the major protective antigens of the virus. Both are antigenically variable, although to different degrees, but the role of antigenic variation in the pathogenesis of hRSV disease has not been fully evaluated. Assessment of immunity to different virus strains is difficult with conventional antibody assays where differing properties of the virus antigens, other than antigenicity, may influence the outcome of the assay. Here, we have developed BIAcore surface plasmon resonance based assays for antibodies to the glycoproteins of hRSV which allow valid comparison of antibody titres against multiple hRSV strains. Glycoproteins from a number of lineages of hRSV sub-group A were captured from lysates of infected cells onto the dextran coated surface of a BIAcore sensor chip via primary monoclonal antibodies (MAbs) to conserved epitopes. For the G glycoprotein, primary MAbs were conjugated directly to the dextran of the sensor chip via free amide groups. For the F glycoprotein, direct conjugation was found to inactivate the MAb and primary MAb was immobilised on the chip via rabbit anti-mouse Fc antibody fragments in an indirect system. Using monoclonal antibodies as secondary MAbs, the glycoproteins in both systems were shown to exhibit a sub-set of conserved and variable epitopes, with some epitopes of both sorts being unavailable, presumably blocked by the primary antibody. Polyclonal anti-hRSV sera raised against viruses of different genotype bound equally to both F and G glycoproteins from homologous and heterologous viruses suggesting that mice immunised systemically with lysates of cells infected with recent isolates of virus do not respond well to genotype specific epitopes.

Detection of human respiratory syncytial virus genotype specific antibody responses in infants

Infection and reinfection of infants with human respiratory syncytial virus (HRSV) occur despite the presence of serum anti-viral glycoprotein antibodies similar to those, which afford protection in animal models of infection. Antigenic variation of the viral glycoproteins between different genotypes of the virus which co-circulate in the population may contribute to the ability of the virus to escape from antibody-mediated protection. In this study, we have investigated whether human infants infected with HRSV produced antibody responses recognising the antigenic differences between different contemporary genotypes of virus. Acute and convalescent sera from 26 infants were analysed for antibody responses to the glycoproteins of the virus isolated from their respiratory tract and to representative viruses of homologous and heterologous genotypes. All infants developed antibodies with similar reactivity for viruses of all contemporary isolates and genotypes when measured in an immunofluorescence assay against unfixed virus infected cells. However, when antibody responses to the individual glycoproteins were measured in a surace plasmon resonance (SPR) assay, although all infants developed genotype cross-reactive antibodies to the F glycoprotein, anti-G antibodies were detectable in only half of the infants and in all cases these were genotype specific. Possession of no or only genotype specific antibodies to the G glycoprotein may contribute to the susceptibility of infants to reinfection. In both assays, reactivity of anti-glycoprotein antibodies with the sub-group A archetypal strain, A2, was markedly lower than with any contemporary virus tested indicating that this strain alone is unsuitable for accurate assessment of infant antibody responses. .