Identification of measles virus-specific hemolysis-inihibiting antibodies separate from hemagglutination-inhibiting antibodies

Analysis of Human RSV Immunity at the Molecular Level: Learning from the Past and Present

Human RSV is one of the most prevalent viral pathogens of early childhood for which no vaccine is available. Herein we provide an analysis of RSV epitope data to examine its application to vaccine design and development. Our objective was to provide an overview of antigenic coverage, identify critical antibody and T cell determinants, and then analyze the cumulative RSV epitope data from the standpoint of functional responses using a combinational approach to characterize antigenic structure and epitope location. A review of the cumulative data revealed, not surprisingly, that the vast majority of epitopes have been defined for the two major surface antigens, F and G. Antibody and T cell determinants have been reported from multiple hosts, including those from human subjects following natural infection, however human data represent a minority of the data. A structural analysis of the major surface antigen, F, showed that the majority of epitopes defined for functional antibodies (neutralizing and/or protective) were either shown to bind pre-F or to be accessible in both pre- and post-F forms. This finding may have has implications for on-going vaccine design and development. These interpretations are in agreement with previous work and can be applied in the larger context of functional epitopes on the F protein. It is our hope that this work will provide the basis for further RSV-specific epitope discovery and investigation into the nature of antigen conformation in immunogenicity.

Implication of vaccination on measles reduction and elimination in Nigeria

BACKGROUND

The availability of a safe and effective vaccine has encouraged the establishment of measles mortality reduction and elimination goals in six World Health Organization regions. In the WHO-AFRO region, they intend to eliminate measles by 2020. This initiative led to the successful elimination of measles in 2012 in the American region. This study mined data from independent investigations in two geographical regions in Nigeria in order to observe the prospects of preventive measures against wild measles virus in a resource limited setting.

MATERIALS AND METHODS

Retrospective data from 757 children between the ages of 10 months and 13years were used. 500 were from children in Kano, Northwest Nigeria and 257 from children in Ibadan, Southwest Nigeria. Data analysis was done using SPSS 16.0.

RESULTS

In all, 386 (75.4%) of the vaccinated children were protected while 121 (23.6%) were not protected. In the unvaccinated children, 63 (25.7%) were protected while 135 (55.1%) were not protected (X²=120.919, p=0.000). In Kano, 81 % of the vaccinated children were protected while 18.4% were not protected. In Ibadan, 95% of the vaccinated were protected (X²=22.129, p = 0.000).

CONCLUSION

The herd immunity in both Kano and Ibadan is good enough to reduce wild measles virus infection. This finding is encouraging because Kano has suffered several epidemics prior to the vaccination campaigns resulting from religious apathy which is the bane of vaccination efforts. Here is evidence that with the right approach in Northern Nigeria, it is possible to sustain national and global immunization drive.

Determination of measles hemagglutination inhibiting antibody levels among school children in Ibadan, Nigeria

Immune status of school children aged from 10-23 years against measles virus was determined by the hemagglutination-inhibition (HI) test with a view of assessing herd immunity. Blood samples from 500 schoolchildren were collected by finger-pricking in Ropacco filter papers. Sera were extracted in 1 mL of cold phosphate buffered saline and treated with 25% (w/v) kaolin and 50.0% monkey red blood cell (RBC) to a final concentration of 1:10. The measles hemagglutinating antigen used for the test was prepared from measles vaccine. Results showed that 62 (12.4%) were positive for measles HI antibody at a titer of 1:640, and 78 (15.6%) had a titer <1:10. There was no significant relationship (P > 0.05) between antibody titer and the schools, while a significant relationship (P < 0.05) existed between antibody titer and age. Although the majority of the schoolchildren had the measles antibody in their sera, titers were, however, beneath the threshold of protection in 33.4% of them. The significant association between age of the schoolchildren and HI titers showed that those antibodies were waning according to age. The study has shown a considerable high level of protection against measles among schoolchildren. To prevent future outbreak of measles among these schoolchildren, it will be advocated that a second dose of measles vaccine be administered.

Kinetics of measles antibody by hemagglutination inhibition assay in children in south-west and north-central Nigeria

OBJECTIVES

We investigated the antibody level of children against wild measles virus in view of recurrent measles epidemics, in order to provide information on immunization status for health policies and for the global measles mortality reduction initiative.

METHODS

Two hundred and seventy-three children between the ages of 10 months and 13 years were recruited for this study from three hospital facilities in south-west and north-central Nigeria. Serum samples were collected from February to July 2009, and laboratory examination commenced in August of the same year. Measles hemagglutinin (HA) antigen was prepared by culturing the measles vaccine virus strain (Edmonston-Zagreb) in a vero/hSLAM cell line. Serum samples were treated to get rid of potentiating factors, non-specific inhibitors, and agglutinins before the HA/hemagglutination inhibition (HI) procedure.

RESULTS

Out of the 175 children vaccinated in Ibadan, 60 (34.3%) had an antibody level not sufficient to protect against measles infection. Likewise, 12 (25.0%) vaccinated children from Ilorin had an antibody level not sufficient to protect against measles infection. There was no significant difference in the level of protection between the children in Ibadan and Ilorin (p>0.05). The geometric mean titer (GMT) was 53.83 for males and 48.64 for females. There was no significant difference between the GMTs of females and males in both locations (p>0.05). Also, no significant difference was observed in the GMTs of children in both locations (p>0.05).

CONCLUSIONS

Of the vaccinated children, 157 (57.5%) developed protective measles virus HI antibody, which is not enough to maintain protective herd immunity. Hence there is a need for catch-up and follow-up vaccination programs, especially in rural areas and places with difficult terrains, in order to reduce measles mortality.

Functions of surface glycoproteins of myxoviruses and paramyxoviruses and their inhibition

Two glycoproteins, HN and F, are present on the surface of paramyxoviruses. HN has receptor-binding amd neuraminidase activities. F is involved in viral penetration, cell fusion and haemolysis and is activated by proteolytic cleavage by a host enzyme into two disulphide-bonded subunits (f1 and F2). The ability of the virus to initiate infection and undergo multiple cycle replication depends on the presence of an activating protease in the host; thus cleavage of F is a major determinant of pathogenesis. The new N-terminus generated on F1 by cleavage is involved in biological activity, and the amino acid sequence of this region of F1 by cleavage is involved in biological activity, and the amino acid sequence of this region of F1 is hydrophobic and highly conserved among para-myxoviruses. In an attempt to design specific inhibitors, oligopeptides and analogous to this region were synthesized and found to be highly active, specific inhibitors of viral penetration, cell fusion and haemolysis. Inhibition is amino-acid-sequence-specific and affected by peptide length, steric configuration and addition of groups to the n-terminal and C-terminal amino acids. Replication of influenza virus was also specifically inhibited by oligopeptides resembling the N-terminus of the HA2 polypeptide. Like that of F1 protein the N-terminus of HA2 is generated by a proteolytic cleavage that activates infectivity. These results have provided information on the action of proteins in viral penetration and membrane fusion and they suggest a possible new approach to chemical inhibition of viral replication. Studies with specific antibodies to each of the paramyxovirus glycoproteins have shown that antibodies to the F protein are essential for effective prevention of the spread of infection. Antibodies to the HN protein, although capable of neutralizing released virus, do not prevent spread to adjacent cells through membrane fusion mediated by the F protein. These findings have implications for the design of effective vaccines against paramyxoviruses and also provided additional insight into the mechanisms involved in the atypical and severe infections observed in individuals who received inactivated paramyxovirus vaccines and were later infected.

Involvement of morbilliviruses in the pathogenesis of demyelinating disease

Two members of the morbillivirus genus of the family Paramyxoviridae, canine distemper virus (CDV) and measles virus (MV), are well-known for their ability to cause a chronic demyelinating disease of the CNS in their natural hosts, dogs and humans, respectively. Both viruses have been studied for their potential involvement in the neuropathogenesis of the human demyelinating disease multiple sclerosis (MS). Recently, three new members of the morbillivirus genus, phocine distemper virus (PDV), porpoise morbillivirus (PMV) and dolphin morbillivirus (DMV), have been discovered. These viruses have also been shown to induce multifocal demyelinating disease in infected animals. This review focuses on morbillivirus-induced neuropathologies with emphasis on aetiopathogenesis of CNS demyelination. The possible involvement of a morbillivirus in the pathogenesis of multiple sclerosis is discussed.

Atypical measles and enhanced respiratory syncytial virus disease (ERD) made simple

Atypical measles and enhanced respiratory syncytial virus disease (ERD) were serious diseases that resulted from exposure of children immunized with inactivated vaccines against measles virus (MV) and respiratory syncytial virus (RSV) to the respective wild-type agents in the 1960s. Although the clinical manifestations of both illnesses were different, the immune responses elicited and primed for by the vaccines shared important similarities. Both vaccines failed to elicit long-lived protective antibody and to promote cytotoxic T lymphocyte responses. In both cases, postvaccination exposure to wild type virus during community outbreaks was associated with immune complex deposition in affected tissues, vigorous CD4 T lymphocyte proliferative responses, and a Th2 bias of the immune response. No relapses of atypical measles or ERD were ever reported. In this manuscript, the pathogeneses of both enhanced diseases and the requirements for the generation of protective antibodies against MV and RSV are discussed, to contribute to the development of newer safe and effective vaccines against these important pathogens.

Antibody reactivity to individual structural proteins of measles virus in the CSF of SSPE and MS patients

BACKGROUND

Chronic progressive disorders of the central nervous system (CNS) impose diagnostic problems, particularly in younger patients. The demonstration of antibodies against measles virus (MV) in the cerebrospinal fluid (CSF) plays a major role in the laboratory diagnosis of subacute sclerosing panencephalitis (SSPE) as well as multiple sclerosis (MS).

OBJECTIVES

Because intrathecally synthesized antibodies against MV can be found in both diseases, it is necessary to establish easy and reliable methods to improve the differential diagnosis.

STUDY DESIGN

Seventy-one paired serum/CSF samples obtained from patients with the diagnosis of SSPE (n = 23), MS (n = 14), or acute postinfectious measles encephalitis (APME, n = 8) have been examined. The reactivity of intrathecally synthesized immunoglobulin to individual recombinant MV structural proteins was assessed using Western blot analysis, ELISA as well as isoelectric focusing (IEF).

RESULTS

All CSF samples obtained from patients suffering from SSPE showed a strong antibody response to MV-nucleocapsid (N) and phosphoprotein (P). Sera from 15 of the 23 SSPE patients were reactive to MV-fusion protein (F). Faint reactivity was obtained against MV-matrix (M) or hemagglutinin protein (H) in the minority of samples (40 and 20%, respectively). CSF samples of MS patients only revealed a clear response to N, and in two cases to F. The other proteins were not recognized in the CSF samples of MS patients. In contrast to SSPE, the IEF of CSF from MS patients revealed only few MV-specific oligoclonal bands. In the CSF samples from APME patients, intrathecal MV antibodies were not detected.

CONCLUSIONS

This study shows that discrimination between SSPE and MS can be achieved in doubtful cases by IEF using MV-N, P and F proteins.

Morbilliviruses and human disease

Morbilliviruses are a group of viruses that belong to the family Paramyxoviridae. The most instantly recognizable member is measles virus (MV) and individuals acutely infected with the virus exhibit a wide range of clinical symptoms ranging from a characteristic mild self-limiting infection to death. Canine distemper virus (CDV) and rinderpest virus (RPV) cause a similar but distinctive pathology in dogs and cattle, respectively, and these, alongside experimental MV infection of primates, have been useful models for MV pathogenesis. Traditionally, viruses were identified because a distinctive disease was observed in man or animals; an infectious agent was subsequently isolated, cultured, and this could be used to recapitulate the disease in an experimentally infected host. Thus, satisfying Koch's postulates has been the norm. More recently, particularly due to the advent of exceedingly sensitive molecular biological assays, many researchers have looked for infectious agents in disease conditions for which a viral aetiology has not been previously established. For these cases, the modified Koch's postulates of Bradford Hill have been developed as criteria to link a virus to a specific disease. Only in a few cases have these conditions been fulfilled. Therefore, many viruses have over the years been definitely and tentatively linked to human diseases and in this respect the morbilliviruses are no different. In this review, human diseases associated with morbillivirus infection have been grouped into three broad categories: (1) those which are definitely caused by the infection; (2) those which may be exacerbated or facilitated by an infection; and (3) those which currently have limited, weak, unsubstantiated or no credible scientific evidence to support any link to a morbillivirus. Thus, an attempt has been made to clarify the published data and separate human diseases actually linked to morbilliviruses from those that are merely anecdotally associated.

Neutralizing B cell response in measles

Co-evolving mechanisms of immune clearance and of immune suppression are among the hallmarks of measles. B cells are major targets cells of measles virus (MV) infection. Virus interactions with B cells result both in immune suppression and a vigorous antibody response. Although antibodies fully protect against (re)infection, their importance during the disease and in the presence of a potent cellular response is less well understood. Specific serum IgM appears with onset of rash and confirms clinical diagnosis. After isotype switching, IgG1 develops and confers life-long protection. The most abundant antibodies are specific for the nucleoprotein, but neutralizing and protective antibodies are solely directed against the two surface glycoproteins, the hemagglutinin and the fusion protein. Major neutralizing epitopes have been mapped mainly on the hemagglutinin protein with monoclonal antibodies, producing an increasingly comprehensive map of functional domains.

Mapping of B-cell epitopic sites and delineation of functional domains on the hemagglutinin-neuraminidase protein of peste des petits ruminants virus

A recombinant baculovirus expressing membrane bound form of hemagglutinin-neuraminidase (HN) protein of peste des petits ruminants virus (PPRV) was employed to generate monoclonal antibodies (mAbs) against PPRV-HN protein. Four different mAbs were employed for mapping of regions on HN carrying B-cell epitopes using deletion mutants of PPRV-HN and RPV-H proteins expressed in Escherichia coli as well as PPRV-HN deletion proteins expressed transiently in mammalian cells. The immuno-reactivity pattern indicated that all mAbs bind to two discontinuous regions of amino acid sequence 263-368 and 538-609 and hence the epitopes identified are conformation-dependent. The binding regions for three mAbs were shown to be immunodominant employing competitive ELISA with vaccinated sheep sera. Delineation of functional domains on PPRV-HN was carried out by assessing the ability of these mAbs to inhibit neuramindase activity and hemagglutination activity. Two mAbs inhibited NA activity by more than 63% with substrate N-acetyl neuraminolactose, while with Fetuin one mAb showed inhibition of NA activity (95%). Of the three antigenic sites identified based on competitive inhibition assay, site 2 could be antigenically separated into 2a and 2b based on inhibition properties. All the four mAbs are virus neutralizing and recognized PPRV-HN in immunofluorescence assay.

Mapping of B-cell epitopes of hemagglutinin protein of rinderpest virus

Monoclonal antibodies (mAbs) against secreted hemagglutinin (H) protein of rinderpest virus (RPV) expressed by a recombinant baculovirus were generated to characterize the antigenic sites on H protein and regions of functional significance. Three of the mAbs displayed hemagglutination inhibition activity and these mAbs were unable to neutralize virus infectivity. Western immunoblot analysis of overlapping deletion mutants indicated that three mAbs recognize antigenic regions at the extreme carboxy terminus (between amino acids 569 and 609) and the fourth mAb between amino acids 512 and 568. Using synthetic peptides, aa 569-577 and 575-583 were identified as the epitopes for E2G4 and D2F4, respectively. The epitopic domains of A12A9 and E2B6 mAbs were mapped to regions encompassing aa 527-554 and 588-609. Two epitopes spanning the extreme carboxy terminal region of aa 573 to 587 and 588 to 609 were shown to be immunodominant employing a competitive ELISA with polyclonal sera form vaccinated cattle. The D2F4 mAb which recognizes a unique epitope on RPV-H is not present on the closely related peste des petits ruminant virus HN protein and this mAb could serve as a tool in the seromonitoring program after rinderpest vaccination.

Functional properties of the fusion and attachment glycoproteins of Nipah virus

Nipah virus (NV) and Hendra virus (HV) are recently emergent, related viruses that can cause severe disease in humans and animals. The goal of this study was to investigate the immunogenic and functional properties of the fusion (F) and attachment (G) glycoproteins of NV. Vaccination of mice with recombinant vaccinia viruses (rVVs) expressing either the F (rVV/NV-F) or G (rVV/NV-G) proteins of NV induced neutralizing antibody responses to NV, with higher titers produced after vaccination with rVV/NV-G. When the homologous pairs of F and G proteins from either HV or NV were coexpressed in a transient expression system, fusion was detected in less than 12 h. An equivalent amount of fusion was observed when the heterologous pairs of F and G proteins from HV and NV were coexpressed. Membrane fusion was inhibited by antiserum from mice vaccinated with rVV/NV-G and rVV/NV-F. Therefore, as with other paramyxoviruses, the membrane glycoproteins of NV are the targets of neutralizing antibodies and membrane fusion mediated by NV requires the presence of both the F and the G proteins. Data from these biological assays support the taxonomic grouping of both HV and NV in the new genus, Henipavirus, within the family Paramyxoviridae.

Immunopathogenesis of vaccine-enhanced RSV disease

Inducing a strong immune response is an essential aim of vaccination. Although immune responses to virus infections are usually protective, they can also be harmful. The best-documented examples of an immune response increasing disease severity are with dengue, measles and respiratory syncytial virus infections. In the 1960s, administration of formalin-inactivated, tissue culture grown RSV (FI-RSV) was found to induce strong ELISA binding but poor virus-neutralising antibody. Infants given this 'lot 100' vaccine appeared to exhibit an increased rate of RSV infection during subsequent natural RSV outbreaks. Although it has not been possible to exactly delineate the cause of disease enhancement in man, animal models strongly suggest that it was due to strong (and perhaps unbalanced) T cell priming rather than infection-enhancing or sensitising antibody. In animal models, enhanced disease can result from over-exuberant T cell priming which recruits an abundant inflammatory infiltrate in the lung (the nature of which depends on the patterns of cytokines and chemokines produced). Formalin-treated RSV vaccination has been linked specifically to the induction of Th2 cells, which make IL-4 and IL-5 and induce a strong pulmonary eosinophilic response. The vaccine dosing regime and the interval between vaccination and challenge can be critical to the induction of protection or pathology. Defining the correlates of protection and disease enhancement in man is critical to the rational development of effective and protective vaccines against RSV.

Successful DNA immunization against measles: neutralizing antibody against either the hemagglutinin or fusion glycoprotein protects rhesus macaques without evidence of atypical measles

Measles remains a principal cause of worldwide mortality, in part because young infants cannot be immunized effectively. Development of new vaccines has been hindered by previous experience with a formalin-inactivated vaccine that predisposed to a severe form of disease (atypical measles). Here we have developed and tested potential DNA vaccines for immunogenicity, efficacy and safety in a rhesus macaque model of measles. DNA protected from challenge with wild-type measles virus. Protection correlated with levels of neutralizing antibody and not with cytotoxic T lymphocyte activity. There was no evidence in any group, including those receiving hemagglutinin-encoding DNA alone, of 'priming' for atypical measles.

Production of atypical measles in rhesus macaques: evidence for disease mediated by immune complex formation and eosinophils in the presence of fusion-inhibiting antibody

The severe disease atypical measles occurred when individuals immunized with a poorly protective inactivated vaccine contracted measles, and was postulated to be due to a lack of fusion-inhibiting antibodies. Here, rhesus macaques immunized with formalin-inactivated measles vaccine developed transient neutralizing and fusion-inhibiting antibodies, but no cytotoxic T-cell response. Subsequent infection with measles virus caused an atypical rash and pneumonitis, accompanied by immune complex deposition and an increase in eosinophils. Fusion-inhibiting antibody appeared earlier in these monkeys than in non-immunized monkeys. These data indicate that atypical measles results from previous priming for a nonprotective type 2 CD4 T-cell response rather than from lack of functional antibody against the fusion protein.

Enhanced antigenicity of a four-contact-residue epitope of the measles virus hemagglutinin protein by phage display libraries: evidence of a helical structure in the putative active site

Antigenicity and conformational propensities of synthetic peptides corresponding to the sequential epitope H236-255 of the measles virus hemagglutinin protein were investigated. This epitope corresponds to the neutralising and protective monoclonal antibody BH129 and includes Arg243, implicated in CD46-down-regulation and Arg253 that has been mapped to the putative enzymatic site. Fine mapping with truncation-, elongation-, Gly- and Ala-substitution analogues defined EL-QL as the critical residues of the minimal epitope S244ELSQL249. CD spectra of peptides, comparison with the 3D-structure of homologous sequences, and prediction algorithms suggested a helical structure with the contact residues E245L-QL249 located on the protein surface. Mimotopes obtained with a 6-mer phage display library contained a consensus Pro (important for binding) instead of Ser247 of the wild-type sequence (irrelevant for binding). The kink induced by Pro seemed to be essential to bring the 4 contact-residues in the mimotopes and in the corresponding short peptides together. CD analysis and prediction algorithms suggested that non-helical conformations of the phage insert and of the peptides may favourably mimic the antigenic helical turns of the wild-type sequence, resulting in an up to 135 times higher antigenicity of the mAb towards the mimotope peptides.

Measles virus fusion protein- and hemagglutinin-transfected cell lines are a sensitive tool for the detection of specific antibodies by a FACS-measured immunofluorescence assay

A FACS-measured immunofluorescence assay was developed for the detection of antibodies directed against the hemagglutinin (H) and fusion (F) glycoproteins of measles virus (MV). Human melanoma cell lines transfected with either the MV H or F genes, which showed a high surface expression of the respective proteins in their native conformation, were used as target cells. The cells were incubated with diluted plasma samples, and stained subsequently with FITC-conjugated secondary antibodies. The FACS-measured fluorescence signals correlated directly with the amount of specific immunoglobulins over a wide concentration range. The use of different conjugates enabled the separate detection of MV-specific IgG, IgM, IgA and IgG subclasses, with relatively low backgrounds. Hemagglutinin-specific IgG, IgM and IgA fluorescence signals were shown to correlate well with MV-specific IgG ELISA titers and MV-specific IgM or IgA capture ELISA OD450-values, respectively. The polyclonal conjugates with specificity for human immunoglobulins offered sufficient cross-reactivity to detect MV-specific IgG, IgM and IgA in plasma samples of cynomolgus macaques, making this technique a useful tool for studying serological responses in vaccination and challenge experiments in non-human primate models.

Use of synthetic peptides to identify measles nucleoprotein T-cell epitopes in vaccinated and naturally infected humans

Recombinant measles nucleoprotein (N) and synthetic peptides spanning the length of the N-protein-coding region were used with a proliferation assay to identify human T-cell epitopes in vaccinated and naturally infected adults. A number of epitopes were mapped to specific regions of the measles virus N. The proliferative response of at least two donors was mediated by CD4(+) T cells in association with HLA DR antigens. Over 70% of all donors tested responded to peptides representing amino acids 271-290, 367-386, 400-420, and 483-502, suggesting that these peptides may be broadly recognized within an HLA diverse population. The most frequently recognized T-cell epitopes in both naturally infected and vaccinated donors were located in the genetically heterogeneous carboxy-terminal half of the N. Analysis of patterns of peptide reactivity among vaccinated and naturally infected subjects identified several regions of potential difference between these two groups. Peptides 221-240 and 237-256 were recognized among 100% of naturally infected donors but among only 37.5% of vaccinated donors and therefore may be of further interest in studies to investigate induction of lifelong versus transient immunity to measles. Use of chimeric molecules containing multiple well-characterized T- and B-cell epitopes or genetic alteration of attenuated vaccine virus to enhance critical T-cell responses may eventually lead to the development of a vaccine candidate that can more closely model the patterns of immune response elicited by wild-type virus.

Measles virus recognizes its receptor, CD46, via two distinct binding domains within SCR1-2

Measles virus (MV) enters cells by attachment of the viral hemagglutinin to the major cell surface receptor CD46 (membrane cofactor protein). CD46 is a transmembrane glycoprotein whose ectodomain is largely composed of four conserved modules called short consensus repeats (SCRs). We have previously shown that MV interacts with SCR1 and SCR2 of CD46. (M. Manchester et al. (1995) Proc. Natl. Acad. Sci. USA 92, 2303-2307) Here we report mapping the MV interaction with SCR1 and SCR2 of CD46 using a combination of peptide inhibition and mutagenesis studies. By testing a series of overlapping peptides corresponding to the 126 amino acid SCR1-2 region for inhibition of MV infection, two domains were identified that interacted with MV. One domain was found within SCR1 (amino acids 37-56) and another within SCR2 (amino acids 85-104). These results were confirmed by constructing chimeras with complementary regions from structurally similar, but non-MV-binding, SCRs of decay accelerating factor (DAF; CD55). These results indicate that MV contacts at least two distinct sites within SCR1-2.

Functional and structural interactions between measles virus hemagglutinin and CD46

We analyzed the roles of the individual measles virus (MV) surface glycoproteins in mediating functional and structural interactions with human CD46, the primary MV receptor. On one cell population, recombinant vaccinia virus vectors were used to produce the MV hemagglutinin (H) and fusion (F) glycoproteins. As fusion partner cells, various cell types were examined, without or with human CD46 (endogenous or recombinant vaccinia virus encoded). Fusion between the two cell populations was monitored by a quantitative reporter gene activation assay and by syncytium formation. MV glycoproteins promoted fusion with primate cells but not with nonprimate cells; recombinant CD46 rendered nonprimate cells competent for MV glycoprotein-mediated fusion. Markedly different fusion specificity was observed for another morbillivirus, canine distemper virus (CDV): recombinant CDV glycoproteins promoted fusion with primate and nonprimate cells independently of CD46. Fusion by the recombinant MV and CDV glycoproteins required coexpression of H plus F in either homologous or heterologous combinations. To assess the role of H versus F in determining the CD46 dependence of MV fusion, we examined the fusion specificities of cells producing heterologous glycoprotein combinations. The specificity of HMV plus FCDV paralleled that observed for the homologous MV glycoproteins: fusion occurred with primate cells but not with nonprimate cells unless they produced recombinant CD46. By contrast, the specificity of HCDV plus FMV paralleled that for the homologous CDV glycoproteins: fusion occurred with either primate or nonprimate cells with no dependence on CD46. Thus, for both MV and CDV, fusion specificity was determined by H. In particular, the results demonstrate a functional interaction between HMV and CD46. Flow cytometry and antibody coprecipitation studies provided a structural correlate to this functional interaction: CD46 formed a molecular complex with HMV but not with FMV or with either CDV glycoprotein. These results highlight the critical role of the H glycoprotein in determining MV specificity for CD46-positive cells.

Molecular identification of two distinct hemagglutinin types of measles virus by polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP)

Contemporary isolates of measles virus, characterized by their inability to hemagglutinate, have been shown to possess a hemagglutinin type distinct from that of classical strains such as the Edmonston strain in that there is a new glycosylation site at amino acid residue 416. This change abolishes a Sau3Al site that is found in the corresponding position of the hemagglutination-positive classical strains. This molecular information prompted us to develop a restriction fragment length polymorphism (RFLP) assay that is capable of distinguishing these two distinct hemagglutinin types. The assay consists of the amplification of a 349-bp segment of the hemagglutinin gene by reverse transcription followed by the polymerase chain reaction and Sau3Al digestion of this amplification product. The resulting two distinct RFLP patterns identified the hemagglutinin types with regard to the presence or absence of the potential new glycosylation site. This assay was applied to determine the relative frequencies over a 28-year period of these two hemagglutinin types present in the archival acute serum specimens taken from patients with measles. This study revealed that strains carrying the classical hemagglutinin type predominated until the early 1980s when it became completely replaced with strains possessing the contemporary hemagglutinin type. Because of its direct applicability to the clinical specimens avoiding selection bias during cell-culture adaptation, this assay provides a valuable asset in both clinical laboratory and epidemiological settings.

Neutralization enzyme-linked immunosorbent assay for evaluation of immunity to measles virus

A neutralization enzyme-linked immunosorbent (Nt-ELISA) assay for determination of protective immunity to measles virus was developed and evaluated. This procedure uses the same initial steps as performed to determine antibody titers by seroneutralization (Nt) test. However, a reduction in virus infectivity by neutralizing antibody was determined by quantitation of viral antigen using ELISA. The serum dilution that resulted in neutralization of 50% of infectious virus could be determined from the absorbance values. To be able to screen a large number of specimens, the conditions of the Nt-ELISA test were adjusted such that negative sera for measles antibodies and the positive ones were clearly distinguished on the basis of a single dilution (1:4). This test showed similar sensitivity (88.3%) and equal specificity as the Nt test when screening 136 serum samples from normal subjects. The estimation of protective antibody titers by Nt and Nt-ELISA methods was strongly correlated (correlation coefficient = 0.91). Thus, the measles Nt-ELISA test is rapid, reproducible, sensitive, and specific for detection of protective measles antibodies.

Immune responses during measles virus infection

The characteristic disease features of measles--fever and rash--are associated with the immune response to infection and are coincident with virus clearance. MV-specific antibody and CD4 and CD8 T cell responses are generated and contribute to virus clearance and protection from reinfection. During this same phase of immune activation immunologic abnormalities are also apparent. There is a generalized suppression of cellular immune responses that may contribute to increased susceptibility to other infections. Autoimmune disease may appear in the form of acute disseminated encephalomyelitis. If virus-specific immune responses are inadequate infection may progress with pulmonary or CNS manifestations, but without a rash. The pathogenesis of the rare disease SSPE, that occurs many years after primary infection is not clear, but immune responses show increased antibody to measles and cellular immune responses similar to those seen after uncomplicated infection.

Cloning and characterization of the cDNA encoding the HA protein of a hemagglutination-defective measles virus strain

cDNA clones corresponding to the mRNA for the hemagglutinin of the hemagglutination-defective strain AK-1 of measles virus were isolated and characterized. Compared with the prototype Edmonston strain, 60 nucleotide substitutions that resulted in 18 amino acid changes were detected. An additional potential N-linked glycosylation site was added by point mutation, which was supported by the observation that the hemagglutinin of the AK-1 strain was stained more heavily after NaDodSO4-PAGE and periodic acid-Schiff (PAS) staining than the Edmonston strain. Computer-assisted analysis revealed that three reverse turns in the secondary structure had disappeared in the hemagglutinin of the AK-1 strain. Moreover, one of these structural changes occurred in the closely glycosylated region at amino acid residues 168-240, which appeared to be a biologically important functional domain. The isoelectric point calculated from the predicted amino acid sequence became about 1 pH unit more basic in the AK-1 strain than the Edmonston strain. This present study is the first sequence analysis of the hemagglutinin gene in a hemagglutination-defective strain of the measles virus.

Intertypic differentiation and detection of intratypic variants among canine and phocid morbillivirus isolates by kinetic neutralization using a novel immunoplaque assay

Intertypic antigenic differences and the intratypic variability of the closely related canine (CVD) and phocid distemper viruses (PDV) were examined using a molecular (monoclonal antibodies specific for the H- and F-glycoproteins) and a functional (kinetic neutralization, KN) approach. KN studies were carried out using a novel immunoplaque technique which combined conventional plaque assay and antigen-specific enzyme-immunostaining techniques. Morbillivirus isolates of canine and phocid origin clearly formed two separate groups. Minor antigenic differences were also evident within each cluster. A distemper isolate of mustelid origin was distinguishable from both CDV- and PDV-like prototype viruses by kinetic neutralization.

Nonreplicating viral vectors as potential vaccines: recombinant canarypox virus expressing measles virus fusion (F) and hemagglutinin (HA) glycoproteins

The development of canarypox virus (CPV) recombinants expressing the hemagglutinin (HA) and fusion (F) glycoproteins of measles virus (MV) is described. Inoculation of the CPV-MV recombinants into avian or nonavian tissue culture substrates led to the expression of authentic MVF and MVHA as determined by radioimmunoprecipitation and surface immunofluorescence. In contrast to avian-derived tissue culture, no productive replication of the CPV recombinant was evident in tissue culture cells derived from nonavian origin. On inoculation of dogs, a species restricted for avipoxvirus replication, the recombinants elicited a protective immune response against a lethal canine distemper virus (CDV) challenge. The level of MV neutralizing antibodies and the level of protection induced against CDV challenge achieved by the host-restricted CPV vector were equivalent to that obtained by vaccinia virus vectors expressing the same MV antigens.

Exposure to acidic pH causes irreversible conformational changes in the measles virus hemagglutinin

Temporary exposure to acidic pH caused the hemagglutinin (H) protein of measles virus to lose hemagglutinating activity and undergo antigenic changes. The antigenic changes, detected as alterations in reactivity of several anti-H protein monoclonal antibodies, were characterised by ELISA and radioimmune precipitation assay. The possible biological instances of such conformational changes within the paramyxovirus H protein are discussed.

Vaccinia virus recombinants expressing either the measles virus fusion or hemagglutinin glycoprotein protect dogs against canine distemper virus challenge

cDNA clones of the genes encoding either the hemagglutinin (HA) or fusion (F) proteins of the Edmonston strain of measles virus (MV) were expressed in vaccinia virus recombinants. Immunofluorescence analysis detected both proteins on the plasma membranes of unfixed cells as well as internally in fixed cells. Immunoprecipitation of metabolically radiolabeled infected-cell extracts by using specific sera demonstrated a 76-kDa HA polypeptide and gene products of 60, 44, and 23 kDa which correspond to a MV F precursor and cleavage products F0, F1, and F2, respectively. Neither recombinant induced cell fusion of Vero cells when inoculated individually, but efficient cell fusion was readily observed upon coinfection of cells with both recombinants. Inoculation of dogs with the vaccinia virus-MV F recombinant (VV-MVF) did not give rise to detectable MV-neutralizing antibody. Inoculation of dogs with the vaccinia virus-MV HA recombinant (VV-MVHA) or coinoculation with both recombinants (VV-MVF and VV-MVHA) induced significant MV-neutralizing titers that were increased following a booster inoculation. Inoculation of dogs with the vaccinia virus recombinants or with MV failed to induce canine distemper virus (CDV)-neutralizing antibodies. Upon challenge with a lethal dose of virulent CDV, signs of infection were observed in dogs inoculated with (VV-MVF). No symptoms of disease were observed in dogs that had been vaccinated with VV-MVHA or with VV-MVHA and VV-MVF and then challenged with CDV. All dogs vaccinated with the recombinant viruses as well as those inoculated with MV or a vaccine strain of CDV survived CDV challenge.

Evaluation of monoclonal antibody-based capture enzyme immunoassays for detection of specific antibodies to measles virus

Monoclonal antibodies to the hemagglutinin protein, fusion protein, phosphoprotein, matrix protein, and nucleoprotein of measles virus were evaluated as detector antibodies in capture enzyme immunoassays (EIAs) for the detection of specific serum immunoglobulin G (IgG), IgA, and IgM antibodies to measles virus. A pool of monoclonal antibodies to hemagglutinin protein and nucleoprotein proved optimal and was further evaluated. Specific IgM was detected in 97% of adolescents with clinical measles, 97% of infants 3 weeks postvaccination, and less than 1% of normal serum specimens. Specific IgA antibodies were found in 97% of adolescents with clinical measles, 97% of infants 3 weeks postvaccination, and less than 1% of normal serum specimens. Specific IgA antibodies were found in 97% of clinical measles cases and vaccinees, in 26% of healthy persons, and in 36% of infants 8 months postvaccination; consequently, IgA antibodies were not a useful indicator of recent measles infection. A significant increase in IgG antibodies between paired specimens was detected in 92% of clinical cases and all vaccinees. Only 59% of infant specimens had persistent IgG antibodies as detected by capture EIA at 8 months postvaccination, whereas all specimens had antibodies as detected by hemagglutination inhibition and plaque neutralization. An alternative indirect EIA, in which antigen was directly absorbed to the solid phase, was more sensitive than the capture design, detecting IgG antibodies in all infants postvaccination. When standardized with a microneutralization assay for the detection of persistent antibodies, the indirect IgG EIA gave predictive values for positive and negative tests exceeding 90%. Our capture IgM and indirect IgG EIAs provide a practical combination of serologic tests for the determination of acute measles virus infection and past exposure to measles virus or vaccine, respectively.

Contribution of measles virus fusion protein in protective immunity: anti-F monoclonal antibodies neutralize virus infectivity and protect mice against challenge

To study the contribution of the measles virus fusion (F) protein in the immune response, anti-F monoclonal antibodies were prepared by using a vaccinia-measles virus F recombinant. In contrast to previously described anti-F monoclonal antibodies, these antibodies not only neutralized virus infectivity and inhibited fusion but also passively protected mice. Since these monoclonal antibodies recognize a configurational epitope, presentation of the antigen during infection may play an important role in the immune response. These factors are discussed in relation to vaccination.

Monoclonal antibodies against measles virus haemagglutinin react with synthetic peptides

The ability of 17 monoclonal antibodies (MoAb) against measles virus haemagglutinin (MV-H) to bind to 10 selected MV-H-specific synthetic peptides was tested in an enzyme immunoassay (EIA). Three peptides representing residues 126-135 (close to the NH2 terminus), 309-318 (middle), and 587-596 (C-terminal) reacted with MoAb designated 48, I29, and 18, respectively. Binding of MoAb I29 to purified virus was abolished after pre-incubation with the peptide 309-318. Similarly, MoAb 48 did not bind to the virus after absorption with the peptide 126-135. Longer peptides of 19 residues from the regions reacting with the MoAb were also synthesized and tested in EIA. None of the MoAb recognized these longer peptides when the latter were bound as free peptides on solid phase. However, MoAb I29 binding to purified virus was blocked equally well by peptides 304-322 and 309-318. In contrast, peptide 121-139 absorbed the reactivity of the MoAb 48 much more weakly than the shorter peptide 126-135, suggesting that the conformation of the longer peptide in solution is different. To analyse affinities in the antigen-antibody reactions, the plates were washed with buffers of varying pH after absorption of the MoAb to MV or peptides. The MoAb I29 bound both to MV and peptide 309-318 with equal affinity, but MoAb 48 and 18 bound to the peptides 126-135 and 587-596 with lower affinity than to the virus. This study indicates that regions corresponding to amino acids 126-135, 309-318, and 587-596 define antigenic sites of the H protein.

Neutralization epitopes of the F glycoprotein of respiratory syncytial virus: effect of mutation upon fusion function

Eighteen neutralizing monoclonal antibodies (MAbs) specific for the fusion glycoprotein of the A2 strain of respiratory syncytial virus (RSV) were used to construct a detailed topological and operational map of epitopes involved in neutralization and fusion. Competitive binding assays identified three nonoverlapping antigenic sites (A, B, and C) and one bridge site (AB). Thirteen MAb-resistant mutants (MARMs) were selected, and the neutralization patterns of the MAbs with either MARMs or RSV clinical strains identified a minimum of 16 epitopes. MARMs selected with antibodies to six of the site A and AB epitopes displayed a small-plaque phenotype, which is consistent with an alteration in a biologically active region of the F molecule. Analysis of MARMs also indicated that these neutralization epitopes occupy topographically distinct but conformationally interdependent regions with unique biological and immunological properties. Antigenic variation in F epitopes was examined by using 23 clinical isolates (18 subgroup A and 5 subgroup B) in cross-neutralization assays with the 18 anti-F MAbs. This analysis identified constant, variable, and hypervariable regions on the molecule and indicated that antigenic variation in the neutralization epitopes of the RSV F glycoprotein is the result of a noncumulative genetic heterogeneity. Of the 16 eptiopes, 8 were conserved on all or all but 1 of 23 subgroup A or subgroup B clinical isolates.

Protective role of human antibody to the fusion protein of measles virus

Absorption of a pooled human gamma globulin preparation with acetone-treated measles virus-infected cells removed all antibodies to measles virus antigens except a portion of the antibody to the fusion (F) protein. The residual anti-F antibody had hemolysis-inhibiting and virus-neutralizing activities, inhibited spread of infection through cell fusion, and was effective in protection of passively immunized mice from fatal measles encephalitis, providing evidence for the protective role of human antibody to the F protein of measles virus.

Preparation and characterization of monoclonal antibodies to nucleocapsid protein N and H glycoprotein of rinderpest virus

Fifteen stable mouse spleen cell myeloma hybrids (hybridomas) producing monoclonal antibodies to rinderpest virus proteins were produced. The specificity of these monoclonal antibodies was established by radioimmunoprecipitation followed by polyacrylamide gel analysis and immunofluorescence. Nine antibodies were specific for the surface glycoprotein H. All the nine clones showed inhibition of haemagglutination by measles virus. The antibodies from two clones (A7D2 and B2F6) neutralise infectious virus. Six clones produce antibodies reacting with the nucleocapsid protein N. Three antigenic sites designated I-III, with sites I and II partially overlapping, were topographically mapped on the H molecule by competitive binding assay. Similarly, two antigenic sites I and II were delineated on the N protein. The monoclonal antibodies were used to study the antigenic relationships of H and N proteins of rinderpest virus, measles virus and canine distemper virus.

Passive hemagglutination test for measles immunity and serodiagnosis

A passive hemagglutination (PHA) test for measles was evaluated in comparison with hemagglutination inhibition (HI) and neutralization (NT) tests. The PHA test determines exclusively the level of antibody directed to the hemagglutinin protein of measles virus. The ratio of PHA to HI titer was 1 to 32 (geometric mean, 6.5) for the first 5 weeks of infection but declined to near unity thereafter. It gradually increased again to 4 to 32 (geometric mean, 11.7) over several years. The initial high PHA titer relative to the HI titer was most likely due to the presence of the immunoglobulin M antibody known to be efficient in agglutination, because 2-mercaptoethanol (2ME) treatment of sera reduced the PHA titer to a level similar to that of the HI titer. The PHA titer in sera obtained after the convalescent phase was insensitive to 2ME, and the relative increase in the PHA over the HI titer was presumably a result of increased antibody avidity. In some individuals, the HI titer fell to below detectable levels several years after either natural infection or vaccination, but the PHA as well as the NT titer remained positive. The PHA titer was therefore a more reliable and more sensitive indicator of immune status against measles than the HI titer. The decrease in PHA titer by 2ME treatment provided evidence of a current or very recent infection. PHA was found to be useful both for assessing immunity status and for serodiagnosis.

Intracellular processing of measles virus fusion protein

Intracellular processing of measles virus fusion (F) protein was studied by radiolabeling and immunoprecipitation with a monoclonal antibody against F protein. The cleavage of F protein into F1 and F2 subunits was complete after 5 hours of chase during which the growth of oligosaccharide chains on the F2 domain of F protein continued. The addition of terminal sialic acid conferred a strong negative charge on the F2 subunit. F protein expressed on the cell surface was removed by a fungal semi-alkaline protease, providing a method to follow the kinetics of its transport to the cell surface. The transport of the F protein was faster than that of the hemagglutinin (HA) protein. Uncleaved F protein, as well as cleaved subunits became digestible by the protease, indicating that a portion of the F protein reaches the cell surface uncleaved. The treatment of measles virus-infected cells with tunicamycin resulted in the synthesis of unglycosylated HA (65 kilodaltons, Kd) and F (48 Kd) proteins. Unglycosylated F protein was not cleaved into smaller subunits, nor was it transported to the cell surface. Unglycosylated HA protein likewise failed to reach the cell surface.

Protection of mice from fatal measles encephalitis by vaccination with vaccinia virus recombinants encoding either the hemagglutinin or the fusion protein

Vaccinia virus recombinants encoding the hemagglutinin or fusion protein of measles virus have been constructed. Infection of cell cultures with the recombinants led to the synthesis of authentic measles proteins as judged by their electrophoretic mobility, recognition by antibodies, glycosylation, proteolytic cleavage, and presentation on the cell surface. Mice vaccinated with a single dose of the recombinant encoding the hemagglutinin protein developed antibodies capable of both inhibiting hemagglutination activity and neutralizing measles virus, whereas animals vaccinated with the recombinant encoding the fusion protein developed measles neutralizing antibodies. Mice vaccinated with either of the recombinants resisted a normally lethal intracerebral inoculation of a cell-associated measles virus subacute sclerosing panencephalitis strain.

Protection against lethal measles virus infection in mice by immune-stimulating complexes containing the hemagglutinin or fusion protein

The importance of each of the two surface glycoproteins of measles virus in active and passive immunization was examined in mice. Infected-cell lysates were depleted of either the hemagglutinin (H) or fusion (F) glycoprotein by using multiple cycles of immunoaffinity chromatography. The products were used to prepare immune-stimulating complexes (iscoms) containing either F or H glycoprotein. Such complexes are highly immunogenic, possibly as a result of effective presentation of viral proteins to the immune system [B. Morein, B. Sundquist, S. Höglund, K. Dalsgaard, and A. Osterhaus, Nature (London) 308:457-460, 1984]. Groups of 3-week-old BALB/c mice were inoculated with the iscom preparations. All animals developed hemolysis-inhibiting antibodies, whereas only sera of animals immunized with the iscoms containing the H glycoprotein had hemagglutination-inhibiting antibodies. Sera from animals immunized with the H or F preparation only precipitated the homologous glycoprotein in radioimmune precipitation assays. The immunized animals were challenged with a lethal dose of the hamster neurotropic variant of measles virus. Of the 7-week-old animals in the nonimmunized control group, 50% died within 10 days after challenge. No animals in the immunized groups showed symptoms of disease throughout the observation period of 3 months. Passive administration of anti-H monoclonal antibodies gave full protection against the 100% lethal acute infection with the hamster neurotropic variant of measles virus in newborn mice, whereas anti-F monoclonal antibodies failed to protect the animals. This study emphasizes that both H and F glycoproteins need to be considered in the development of measles virus subunit vaccines.

Comparison of the relative roles of the F and HN surface glycoproteins of the paramyxovirus simian virus 5 in inducing protective immunity

To compare the relative roles of the paramyxovirus simian virus 5 (SV5) major surface glycoproteins, fusion (F) and hemagglutinin-neuraminidase (HN), in inducing protective immunity, two recombinant vaccinia viruses were constructed. The F and HN polypeptides expressed by the recombinant viruses were indistinguishable from their authentic SV5 counterparts in electrophoretic mobility, glycosylation, and, for the F protein, cleavage of the precursor, F0, to the disulfide-linked subunits F1 and F2. Injection of rabbits and hamsters with live recombinant virus elicited an antibody response to either F or HN and provided a source of monospecific polyclonal antisera to the SV5 proteins. The vaccinia virus-SV5 F (vaccinia-F) recombinant induced higher levels of neutralizing antibody than did the vaccinia-HN recombinant, but animals inoculated with vaccinia-HN were better protected from challenge with SV5. Animals infected with both the vaccinia-HN and vaccinia-F viruses were nearly as well protected from challenge as were animals infected with SV5.

Measurement of polypeptide- and antigenic site-specific antibodies to measles virus using a competitive enzyme immunoassay

A competitive enzyme immunoassay (EIA) for measuring polypeptide- and antigenic site-specific antibodies against measles virus (MV) was developed. Three monoclonal antibodies (MAbs) against the fusion (F) and one MAb against the hemagglutinin (H) protein of MV were labelled with biotin and used in biotin-streptavidin EIA system. The inhibition of the binding of the labelled MAbs by the bound serum samples was measured in EIA and the titers were defined by reading at the level of 25% inhibition. The titers increased from acute to early convalescent measles sera in all the tests and antibody levels to the F protein increased earlier than antibodies to the H protein. The ratio of antibodies against 2 different antigenic sites on the F protein was significantly higher in subacute sclerosing panencephalitis patients than in normal blood donors. Similarly, SJL mice immunized with MV antigen had higher ratios of the corresponding antibodies than Balb/c mice. The results indicate that antibody response to different polypeptides and antigenic sites on the same polypeptide can be studied with the developed method and that the responses against different antigenic sites are independent.

Inhibition of measles virus-induced cell-cell fusion with a monoclonal antibody directed against the haemagglutinin

A neutralizing monoclonal antibody (C26-15) against the haemagglutinin (H protein) of measles virus was generated which caused cell-cell fusion inhibition in cultures of measles virus-infected cells. It was shown that this phenomenon coincided with a down-regulation of the expression of both the H protein and the fusion (F) protein. We also showed cell-cell fusion inhibition with a polyclonal rabbit serum directed against Tween-ether inactivated measles virus, which did not contain biologically active antibodies against the F protein. Cell-cell fusion inhibition caused by anti-H antibodies is distinct from cell-cell fusion inhibition induced by a direct interaction of anti-F antibody with the F protein in the membrane of infected cells. Since both mechanisms may also be involved in the in vivo situation, the exclusive role for the generation of anti-F antibody to prevent virus spread by cell-cell fusion in vivo is questioned. It is speculated that the observed down-regulation of both glycoproteins may lead to a less efficient killing of infected cells by cytotoxic T-lymphocytes, which may constitute an alternative explanation for the insufficient protection after vaccination with an inactivated measles vaccine.

Protection against canine distemper virus in dogs after immunization with isolated fusion protein

Canine distemper virus attachment (hemagglutinin [H] equivalent) and fusion (F) antigens were purified by affinity chromatography with monoclonal antibodies. The purified antigens were used to immunize groups of three dogs. Radioimmune precipitation assays with sera from these animals showed that the F antigen preparation was pure and induced only an F polypeptide-specific antibody response but that the H antigen preparation had a slight contamination by the F antigen. Immunized animals were challenged with virulent canine distemper virus. Two animals in each group developed pronounced humoral and cellular immune responses after challenge. Among these infected animals, only the dogs immunized with H antigen developed symptoms, albeit mild. In contrast, three nonimmunized control animals developed severe disease, with a fatal outcome in two cases. The complete resistance against challenge in two dogs was interpreted to reflect in one case anti-F immunity and in the other case most likely a high level of anti-H immunity. It is suggested that the F antigen may be of particular interest for the development of morbillivirus and possibly other paramyxovirus subunit or synthetic vaccines, because it can induce immunity capable of blocking virus infection and in situations of virus replication prevent the emergence of symptoms.

Monoclonal antibodies against the fusion protein are protective in necrotizing mumps meningoencephalitis

A monoclonal antibody against the fusion (F) protein of mumps virus was found to confer marked protection in mumps virus-induced encephalitis. Almost total prevention of extensive brain necrosis was found. This study indicates that the virus F protein is directly involved in the pathogenesis of brain necrosis.

Enhancement of respiratory syncytial virus pulmonary pathology in cotton rats by prior intramuscular inoculation of formalin-inactiva ted virus

Cotton rats previously inoculated with Formalin-inactivated respiratory syncytial virus (RSV) were challenged intranasally with live RSV to induce an enhancement of RSV disease similar to that observed after the administration of Formalin-inactivated RSV vaccine to human infants 20 years ago. Within 24 h after infection with RSV, cotton rats developed pulmonary lesions that reached a maximum by day 4. Histologically, the lesions resembled an experimental pulmonary Arthus reaction. An action of Formalin on RSV appears to be responsible for this effect, because live virus or virus heated in the absence of Formalin did not induce enhanced immunopathology. Selected epitopes on the fusion (F) or attachment (G) or both RSV surface glycoproteins that are involved in inducing neutralizing antibodies were modified to reduce or ablate their antigenicity. However, other epitopes on the F or G or both glycoproteins were not ablated by Formalin, because cotton rats inoculated parenterally with a Formalin-inactivated virus developed a high level of F and G antibodies measurable by an enzyme-linked immunosorbent assay. At this time, the effect of Formalin on RSV cannot be localized to either the F or G glycoprotein of RSV.

Neonatal respiratory syncytial virus infection: role of transplacentally and breast milk-acquired antibodies

The effect of transplacentally and breast milk-acquired antibodies on respiratory syncytial virus infection was studied in neonatal and 2-month-old cotton rats. Adult female rats infected intranasally with live virus regularly produced virus-specific antibodies in the serum, colostrum, and breast milk. By using foster feeding techniques, we showed that both transplacentally and breast milk-acquired antibodies were effective in reducing the replication of respiratory syncytial virus in the lungs of neonatal animals when they were challenged with live virus via the nasal route at 3 days of age. However, the protection provided by these antibodies was rather brief. There was no difference in the replication of respiratory syncytial virus in the lungs of 2-month-old animals that were delivered and nursed by seropositive (immunized) or seronegative (control) cotton rats.

Monoclonal antibodies against five structural components of measles virus. II. Characterization of five cell lines persistently infected with measles virus

Groups of monoclonal antibodies against measles virus nucleoprotein (NP), phosphoprotein (P), matrix (M), hemagglutinin (H) and fusion (F) components were used for characterization of 5 persistently infected cell lines. In four of these lines (Lu106 carrier, MaSSPE, MaPi, HEpPi) all cells were infected but the cells mostly produced noninfectious virus products. The fifth line (HNT in vero cells) did not produce any infectious virus and only a fraction of the cells were infected in most passages. In agreement with earlier findings the virus strains showed marked variations in the M epitope pattern and also some variation in the H epitope pattern. In addition epitope variations were found in both NP and P protein, which contrasted with conserved antigen characteristics of these components in lytically replicating virus. Restriction of fusion in the persistent infections was studied further. HNT and Lu 106 cells showed selective quantitative restriction in F protein synthesis. Lu106 cells were found to contain distinct epitopic F species. In contrast MaSSPE cells produced readily detectable cleaved F protein and in addition extracellular virus products carried hemolytic activity. The fact that no cell fusion occurred was interpreted to be due to particular properties of the Ma 106 cells, a concept supported by the absence of fusion of these cells when infected with syncytiogenic measles virus. It is concluded that (a) under conditions of persistence of measles-virus without requirement for synthesis of complete virions a more pronounced variation in epitope characteristics of virus components is encountered than in lytic infections; and b) that persistence of measles virus shows individualistic characteristics which may reflect changes in the virus and/or innate properties of the host cells.

Comparison of measles antihemolysin test, enzyme-linked immunosorbent assay, and hemagglutination inhibition test with neutralization test for determination of immune status

Sera were collected from 238 high-school students in Prince Edward Island for the determination of immune status before an anticipated measles outbreak. In addition, history of vaccination status and measles infection was obtained. In the subsequent outbreak, 28 students did contract measles. Specificity for hemagglutination inhibition (HI), antihemolysin (AH), and enzyme-linked immunosorbent assay (ELISA) was 100%, compared with the neutralization test. Corresponding sensitivity values for the tests were 66.0% (HI), 99.5% (AH), and 99.0% (ELISA). Predictive values for susceptibility were 26.9% (HI), 77.8% (AH), 75.7% (ELISA), 80% (neutralization), and 41.4% as determined by history of infection or vaccination. The predictive value for immunity as determined by history of previous infection or vaccination was 91.8%, compared with 100% for the four serological tests. No false-positive results were seen with any of these tests. Compared with the neutralization test, the HI test had 69 false-negative results, the AH had 1, and the ELISA test had 2. The AH and ELISA tests provided sensitive and specific alternatives to the commonly used HI test for immune status determination.