Display of FliC131 on the Surface of Lactococcus lactis as a Strategy to Increase its Adjuvanticity for Mucosal Immunization

Research on innovative mucosal adjuvants is essential to develop new vaccines for safe mucosal application. In this work, we propose the development of a Lactococcus lactis that expresses a variant of flagellin on its surface (FliC131*), to increase the adjuvanticity of the living cell and cell wall-derived particles (CWDP). We optimized the expression of FliC131*, and confirmed its identity and localization by Western blot and flow cytometry. We also generated CWDP containing FliC131* (CDWP-FliC131*) and evaluated their storage stability. Lastly, we measured the human TLR5 stimulating activity in vitro and assessed the adjuvanticity in vivo using ovalbumin (OVA) as a model antigen. As a result, we generated L. lactis/pCWA-FliC131*, that expresses and displays FliC131* on its surface, obtained the corresponding CWDP-FliC131*, and showed that both activated hTLR5 in vitro in a dose-dependent manner. Furthermore, CWDP-FliC131* retained this biological activity after being lyophilized and stored for a year. Finally, intranasal immunization of mice with OVA plus live L. lactis/pCWA-FliC131* or CWDP-FliC131* induced OVA-specific IgG and IgA in serum, intestinal lavages, and bronchoalveolar lavages. Our work demonstrates the potential of this recombinant L. lactis with an enhanced adjuvant effect, prompting its further evaluation for the design of novel mucosal vaccines.

Pre-vaccine rotavirus surveillance in Buenos Aires, Argentina. Characterization of an emergent G1P[8] strain associated to fatal cases in 2014

Group A rotaviruses (RVA) are the most frequent etiological agents causing severe diarrhea in infants and surveillance of genotype, and genetic characteristics of circulating strains are necessary in order to evaluate vaccine programs. The objectives of this work were to describe G and P genotype from 2012 through 2014 in Buenos Aires, Argentina completing an overview of 19 years of genotype surveillance in our region and to characterize an emerging G1P[8] strain associated with severe cases and five fatalities in 2014. We performed genotyping by RT-PCR. The sequencing of several genes, phylogenetic analyses, and comparative epidemiological data were used to know the origin and phylogenetic relationships of the emerging G1P[8] strain. Along with this report, 19 years of continuous RVA genotype surveillance in Argentina in the pre-vaccine era was covered. During the last year of this surveillance, 2014, a significantly increased incidence of RVA associated gastroenteritis was related to the reemergence of G1P[8] strains, being these ones detected in low frequency in the last nine years. Interestingly, the patients affected were significantly older when compared with those from the last six seasons. Additionally, phylogenetic analysis of several genes infer that these G1P[8] strains were closely related to Asian strains circulating during 2012 and 2013. In addition to this, the suggested extra continental origin for the 2014 G1P[8] strains and the very low circulation of G1 type during nine years probably explain the increased incidence and severity in the gastroenteritis cases and the particular epidemiologic characteristics. In conclusion, this work gives us a whole panorama of the pre-vaccine era of the RVA molecular epidemiology in the most populated region of Argentina. In this way, this work inspires us to continue with this type of studies in the post-vaccination era.

Rotavirus VP6 protein mucosally delivered by cell wall-derived particles from Lactococcus lactis induces protection against infection in a murine model

Rotaviruses are the primary cause of acute gastroenteritis in children worldwide. Although the implementation of live attenuated vaccines has reduced the number of rotavirus-associated deaths, variance in their effectiveness has been reported in different countries. This fact, among other concerns, leads to continuous efforts for the development of new generation of vaccines against rotavirus.In this work, we describe the obtention of cell wall-derived particles from a recombinant Lactococcus lactis expressing a cell wall-anchored version of the rotavirus VP6 protein. After confirming by SDS-PAGE, Western blot, flow cytometry and electronic immunomicroscopy that these particles were carrying the VP6 protein, their immunogenic potential was evaluated in adult BALB/c mice. For that, mucosal immunizations (oral or intranasal), with or without the dmLT [(double mutant Escherichia coli heat labile toxin LT(R192G/L211A)] adjuvant were performed. The results showed that these cell wall-derived particles were able to generate anti-rotavirus IgG and IgA antibodies only when administered intranasally, whether the adjuvant was present or not. However, the presence of dmLT was necessary to confer protection against rotavirus infection, which was evidenced by a 79.5 percent viral shedding reduction.In summary, this work describes the production of cell wall-derived particles which were able to induce a protective immune response after intranasal immunization. Further studies are needed to characterize the immune response elicited by these particles as well as to determine their potential as an alternative to the use of live L. lactis for mucosal antigen delivery.

Evaluation of the immunogenicity of a recombinant HSV-1 vector expressing human group C rotavirus VP6 protein

Group C Rotavirus (RVC) has been associated globally with sporadic outbreaks of gastroenteritis in children and adults. RVC also infects animals, and interspecies transmission has been reported as well as its zoonotic potential. Considering its genetic diversity and the absence of effective vaccines, it is important and necessary to develop new generation vaccines against RVC for both humans and animals. The aim of the present study was to develop and characterize an HSV-1-based amplicon vector expressing a human RVC-VP6 protein and evaluate the humoral immune response induced after immunizing BALB/c mice. Local fecal samples positive for RVC were used for isolation and sequencing of the vp6 gene, which phylogenetically belongs to the I2 genotype. We show here that cells infected with the HSV[VP6C] amplicon vector efficiently express the VP6 protein, and induced specific anti-RVC antibodies in mice immunized with HSV[VP6C], in a prime-boost schedule. This work highlights that amplicon vectors are an attractive platform for the generation of safe genetic immunogens against RVC, without the addition of external adjuvants.

Surveillance of group A Rotavirus in Buenos Aires 2008-2011, long lasting circulation of G2P[4] strains possibly linked to massive monovalent vaccination in the region

BACKGROUND

Group A rotaviruses (RVA) are the most frequent single etiological agents of severe diarrhea in infants. Since 2006 RVA vaccines have been introduced in national schedules of middle and high income countries with substantial declines in rotavirus associated disease burden. However, surveillance must be maintained to, eventually, detect emerging types or variants selected by the new pressure imposed by vaccination.

OBJECTIVES

To analyze the molecular epidemiology of group A rotavirus after vaccine introduction in the region in the context of data from more than 15 years of continuous surveillance in Buenos Aires.

STUDY DESIGN

RVA positive diarrhea samples collected in Buenos Aires from 2008 to 2011 were genotyped by RT-PCR. Selected samples were sequenced to gain insight on evolution of common and globally emerging human RVA strains.

RESULTS

Lineage III G12P[8] strain emerged in 2008 in Buenos Aires and shared co-dominancy with G3 strains during 2009. An atypical long lasting circulation of G2P[4] strains since 2004 reached rates around 80% in 2011 in Buenos Aires. Sequencing of the VP7 and VP4 genes of representative G2P[4] isolates suggests Brazil as the origin of the 2010-2011 strains.

CONCLUSIONS

Globally emergent G12 lineage III strains could be established as dominant strains in a very populated area in two years since emergence. In this work it was also shown that the persistence of G2P[4] strains during 8 years could be related to massive immunization with the monovalent vaccine in the region.

Antigenicity and immunogenicity of rotavirus VP6 protein expressed on the surface of Lactococcus lactis

Group A rotaviruses are the major etiologic agents of acute gastroenteritis worldwide in children and young animals. Among its structural proteins, VP6 is the most immunogenic and is highly conserved within this group. Lactococcus lactis is a food-grade, Gram-positive, and nonpathogenic lactic acid bacteria that has already been explored as a mucosal delivery system of heterologous antigens. In this work, the nisin-controlled expression system was used to display the VP6 protein at the cell surface of L. lactis. Conditions for optimal gene expression were established by testing different nisin concentrations, cell density at induction, and incubation times after induction. Cytoplasmic and cell wall protein extracts were analyzed by Western blot and surface expression was confirmed by flow cytometry. Both analysis provided evidence that VP6 was efficiently expressed and displayed on the cell surface of L. lactis. Furthermore, the humoral response of mice immunized with recombinant L. lactis was evaluated and the displayed recombinant VP6 protein proved to be immunogenic. In conclusion, this is the first report of displaying VP6 protein on the surface of L. lactis to induce a specific immune response against rotavirus. These results provide the basis for further evaluation of this VP6-displaying L. lactis as a mucosal delivery vector in a mouse model of rotavirus infection.

Antigen vehiculization particles based on the Z protein of Junin virus

BACKGROUND

Arenavirus matrix protein Z plays an important role in virus budding and is able to generate enveloped virus-like-particles (VLPs) in absence of any other viral proteins. In these VLPs, Z protein is associated to the plasma membrane inner surface by its myristoyl residue. Budding induction and vesicle formation properties can be exploited to generate enveloped VLPs platform. These structures can be designed to carry specific antigen in the inner side or on the surface of VLPs.Vaccines based on VLPs are a highly effective type of subunit vaccines that mimic the overall structure of virus particles in absence of viral nucleic acid, being noninfectious.In this work we assayed the capacity of Junin Z protein to produce VLPs carrying the green fluorescent protein (eGFP), as a model antigen.

RESULTS

In this report the Junin Z protein ability to produce VLPs from 293T cells and its capacity to deliver a specific antigen (eGFP) fused to Z was evaluated. Confocal microscopy showed a particular membrane bending in cells expressing Z and a spot welded distribution in the cytoplasm. VLPs were detected by TEM (transmission electron microscopy) and were purified from cell supernatant. The proteinase protection assay demonstrated the VLPs integrity and the absence of degradation of the fused antigen, thus indicating its internal localization. Finally, immunization of mice with purified VLPs produced high titres of anti-eGFP antibodies compared to the controls.

CONCLUSIONS

It was proved that VLPs can be generated from cells transfected with a fusion Junin virus Z-eGFP protein in absence of any other viral protein, and the capacity of Z protein to support fusions at the C-terminal, without impairing its budding activity, allowing vehiculization of specific antigens into VLPs.

Correlation between rotavirus A genotypes detected in hospitalized children and sewage samples in 2006, Córdoba, Argentina

Routine rotavirus A (RV-A) surveillance is based on clinical cases, so only symptomatic infections are reported. The objective of this study was to determine whether the RV-A genotypes and cold seasonal pattern described in patients with diarrhea is reflected by sewage surveillance, which could be representative of the RV-A genotypes circulating in the population. The genotype distribution of RV-A in effluent samples from a local sewage treatment plant was compared to those from local clinical cases. A total of 52 sewage samples and 70 stool specimens from children with acute non-bacterial diarrhea were collected from January to December 2006. The effluent specimens were concentrated and RNA extracts from concentrated sewage and clinical samples were genotyped for the rotavirus VP7 gene. The proportional distribution of the RV-A G-genotypes in sewage and clinical samples during the cold season was similar: G1 accounted for 26.6% of the typed sewage isolates and 28.8% of the clinical infections; G3 type accounted for 21.9% and 25.8%; G2 type 15.6% and 10.6%; G4 type 17.2% and 21.2%; G8 type 1.6% and 0%; and the G9 type 17.2% and 13.6%, respectively. A similar picture of RV-A genotype detection was obtained in sewage samples collected during the cold and warm seasons. The results indicate that there is a correlation between genotypes of RV-A isolates from human diarrheic patients and of those from sewage samples. In addition, sewage monitoring highlighted the uniform all-year RV-A circulation, which was in contrast to the peak incidence of RV-A infection in the community.

Molecular epidemiology of group A rotavirus in Buenos Aires, Argentina 2004-2007: reemergence of G2P[4] and emergence of G9P[8] strains

Detection and characterization of group A rotavirus in Buenos Aires, Argentina, was conducted on 710 fecal samples from children 0-15 years old collected between 2004 and 2007. Rotavirus was detected in 140 (19.7%) samples with G9P[8] (30.0%) and G2P[4] (21.4%) as the most common genotypes. Mixed (G and/or P) infections accounted for 17.9% of the samples and the emerging G12 strain was detected during 2004 (3.5%) and 2007 (2.5%). Genotype G2 was the most prevalent during 2004 (43.9%) and 2007 (57.5%) and G9 during 2005 (58.0%) and 2006 (61.5%). Analysis of genotype prevalences from studies performed since 1996 in the same area showed striking natural fluctuations in G and P genotype frequencies. In particular, G2P[4] strains disappeared after 1999 and reemerged in 2004 to become the predominant strain by 2007 with a concomitant major decrease in G1P[8] prevalence. The VP7 genes from Argentinian G9 and G2 strains were sequenced and phylogenetic analysis was conducted in order to compare with sequences from strains isolated in regional countries reported previously. Several changes in the deduced amino acid sequence in antigenic regions of the VP7 protein from Argentinian and Brazilian strains were identified compared to vaccine strains. Overall, this study revealed relationships in the circulation of rotavirus strains in South American countries and major replacements in dominant genotypes, including the virtual disappearance of G1P[8] strains in a non-vaccinated population. High numbers of mixed infections speeding up evolution, circulation of rare serotypes, and antigenic drift could, eventually, become challenges for new vaccines.

Detection and characterization of group C rotavirus in Buenos Aires, Argentina, 1997-2003

The role of group C rotaviruses as a cause of diarrhea was examined among children <17 years of age admitted to a Hospital in a suburban area of Buenos Aires, Argentina between 1997 and 2003. A total of 1,579 fecal samples were screened for group A (RVA) and C (RVC) rotaviruses by two in-house ELISA methods at Quilmes University (UNQ-ELISA). Samples positive, doubtful and negative by RVC specific UNQ-ELISA (n = 246) were examined further for RVC by another in-house ELISA (CDC-ELISA), electron microscopy, RT-PCR, nested PCR, and Southern hybridization. Sensitivity, specificity, and predictive values for each test were determined. While the sensitivity was comparable for the nested PCR and CDC-ELISA methods (82.5%), the molecular methods were slightly more specific. Poorly preserved particles were often seen in fecal samples, suggesting that degradation of RNA could be a factor influencing the performance of molecular methods. The incidence of RVC was estimated to be 3% without apparent differences among seasons. RVC infected patients had a significantly (P < 0.001) higher median age (6 years vs. 1 year) than those with RVA infection. Sequence of the RVC VP7 gene from six Argentinean strains and sequences reported previously in different countries showed high nucleotide (94.4-99.9%) sequence identities, indicating a high degree of conservation for human RVC VP7 genes among strains collected on five continents over a period of 17 years. These findings indicate that RVC is a significant cause of diarrhea and it is necessary to develop simple and sensitive serological methods for its detection.

Characterization of liposomes coated with S-layer proteins from lactobacilli

The stability of liposomes coated with S-layer proteins from Lactobacillus brevis and Lactobacillus kefir was analyzed as a previous stage to the development of a vaccine vehicle for oral administration. The interactions of the different S-layer proteins with positively charged liposomes prepared with soybean lecithin or dipalmitoylphosphatidylcholine were studied by means of the variation of the Z potential at different protein-lipid ratios, showing that both proteins were able to attach in a greater extent to the surface of soybean lecithin liposomes. The capacity of these particles to retain carboxyfluorescein or calcein by exposure to bile salts, pancreatic extract, pH change and after a thermal shock showed that both S-layer proteins increased the stability of the liposomes in the same magnitude. The non-glycosylated protein from L. brevis protects more efficiently the liposomes at pH 7 than those from L. kefir even without treatment with glutaraldehyde.

Molecular epidemiology of group A rotavirus diarrhea among children in Buenos Aires, Argentina, from 1999 to 2003 and emergence of the infrequent genotype G12

To examine the epidemiology of rotaviruses in Buenos Aires, Argentina, we screened 1,212 stool samples from children with diarrhea in the southern district of Buenos Aires from 1999 to 2003. We identified 187 samples (15.4%) that were positive for group A rotavirus by use of antigen enzyme-linked immunosorbent assay. Among these specimens, 112 were available for typing: 93 (83.0%) were single-type infections, 9 (8.0%) were mixed-type infections with more than one G or P type, and 10 (8.9%) were G and/or P nontypeable. In contrast to the findings in our last study, from 1996 to 1998, genotype P[4], G2 strains were almost completely absent and P[8], G1 and P[8], G4 strains were dominant, representing more than 80% of the G and P types found. Genotypes G2 and G9 were detected in few samples, and type G3 was completely absent. We identified several uncommon genotype G12 strains, representing the first detections outside of Asia and the United States, by sequencing. Using a genotype G12-specific reverse transcription-PCR, we identified eight (6.7%) positive samples for the 1999 to 2003 period. The high degree of sequence identity between recent G12 isolates from Argentina, the United States, and Asian countries suggests a relatively recent introduction(s) of these strains into humans from a common progenitor. The Argentinean G12 strains belonged to genotype P[9], similar to most of the recently described Asian G12 strains. The finding of G12 strains in several other regions of the world raises the possibility that G12 may be emerging globally and suggests that surveillance for this strain should be conducted routinely.

Measles virus-specific antibody levels in individuals in Argentina who received a one-dose vaccine

In spite of active measles virus (MV) vaccination strategies, reemergence continues to occur, impairing global eradication programs. The immune status against measles was evaluated in 350 vaccinated healthy Argentine children and teenagers who received a single dose of the MV Schwarz strain Lirugen vaccine (Aventis Pasteur). Sera were assessed for immunoglobulin G (IgG) antibodies by a commercial enzyme immunoassay (EIA) (Enzygnost; Behring), an in-house EIA, and neutralization EIA. Results obtained with these methods showed a marked decline in IgG level with increasing age. At 1 to 4 years of age, 84% of children had IgG antibodies above 200 mIU/ml, conventionally accepted as protective levels, whereas only 32% of older children and teenagers had antibody levels exceeding 200 mIU/ml. Moreover, the MV IgG content in the teenage group was significantly lower than the IgG antibody level of the group of younger children (P < 0.0001). In contrast, screening for IgG antibody levels to inactivated tetanus vaccine showed that, on average, 80% of this population was fully protected and that this high level of protection remained through the teenage years. This study suggests that within this population a considerable proportion of individuals had low measles antibody levels that may be insufficient to protect against reinfections or clinical disease.

Detection of group a human rotavirus G9 genotype circulating in Córdoba, Argentina, as early as 1980

The incidence of human rotavirus G types was determined over a 25-year period (1979-2003) by using reverse transcription-PCR (RT-PCR) to examine 519 stool specimens found to be positive for rotavirus by enzyme linked immunosorbent assay (ELISA) or polyacrylamide gel electrophoresis (PAGE). These stool samples were obtained from children under 3 years old who had been treated for acute diarrhea at public hospitals in Córdoba, Argentina. The present study describes the continued circulation of the common human G types G1 (53.8%), G2 (10.2%), G3 (4.4%), and G4 (27%), and also the detection of the unusual types G8 (0.5%) and G9 (4.2%). Genotype G9 was detected during the 1980-1988 and 1997-2003 periods at relatively low rates. Rotavirus G types distribution was independent of age (1-18 months), gender or out-patient or in-patient status. Unexpectedly, 44.6% of mixed infections were detected, involving common and unusual genotypes. Overall, 95.4% of the typed strains belonged to the most prevalent human serotypes (G1-G4) but the detection of G9 infection throughout this study period highlights the importance of this serotype as a human pathogen.

Monoclonal antibodies for the rapid diagnosis of influenza-B virus infections by ELISA: production and characterization

BACKGROUND

Monoclonal antibodies directed against conserved epitopes of viral proteins have substantially improved the accuracy of several immunochemical methods in diagnostic virology.

OBJECTIVES

To characterize mouse monoclonal antibodies directed against structural protein antigens of influenza-B virus and evaluate their use as diagnostic reagents for the direct detection of such antigens in clinical specimens from patients with respiratory infections of unknown aetiology.

STUDY DESIGN

(a) Production and characterization of monoclonal antibodies against influenza-B viral antigens, and (b) their use in two different ELISA systems for detecting influenza-B antigen either directly in clinical specimens or after confirmation by rapid culture in MDCK cells.

RESULTS

Four monoclonal antibodies were selected for their specificity for the nucleoprotein antigen as demonstrated by Western blot analysis. The specificity of these antibodies for different epitopes of the nucleoprotein was demonstrated by competition experiments, using unlabelled and biotin-labelled purified antibodies in a sandwich assay. All four antibodies belong to the mouse IgG(2a) isotype, lack haemagglutination inhibition and neutralization properties and exhibit titres as high as 10(-6) in ELISA with as little as 30 ng purified influenza-B virus. ELISA methods using these antibodies detected only influenza-B viral antigens in direct testing of clinical specimens from patients with known influenza-B or influenza-A infections, or after reisolating virus from such specimens in tissue culture of MDCK cells.

CONCLUSION

The antibodies were suitable for the direct detection and typing of influenza-B virus in clinical specimens or for use in rapid confirmation cultures.

An immunochemical method for quantitation of Epinotia aporema granulovirus (EpapGV)

Epinotia aporema granulovirus (EpapGV) is a baculovirus that affects E. aporema larvae and has proven to be a good candidate for the biocontrol of this important pest in South America. As part of the quality control of the production of a bioinsecticide based on EpapGV, a sensitive method was developed for the detection and quantitation of the virus. To this end, we used the major occlusion body (OB) protein (granulin) to generate polyclonal antibodies in rabbits. Purified IgG fractions from hyperimmune sera were labeled with biotin and used as detecting antibodies in a double antibody sandwich enzyme linked immunosorbent assays (ELISA). No cross-reactivity was detected with any of the nucleopolyhedroviruses (NPV) tested in this study, while a minor degree of reactivity was observed with the closely related Cydia pomonella granulovirus (CpGV). The performance of the ELISA was satisfactory in terms of sensitivity, detecting as little as 0.53 ng/ml of EpapGV granulin in suspensions of purified virus OB. This represented 2.0x10(4) OB/ml. Granulin was also detected in complex and highly diluted bioinsecticidal formulate mixtures. In time course experiments, the virus was detected as early as 24 h post infection (p.i.). The results of the studies demonstrate that this method is a convenient, rapid and inexpensive alternative for routine detection and quantitation of EpapGV.

A rapid method to produce high yields of purified rotavirus particles

A rapid purification method of rotavirus particles to high yield retaining the double shelled structure of infectious virus is described. Group A rotavirus (UK strain) was concentrated through a cushion of colloidal silica (rho=1.10 g/cm(3)) or by precipitating with polyethylene glycol 8000. After concentration, infectious rotavirus was cleared from host cell proteins by density equilibrium centrifugation in gradients of colloidal silica using near vertical rotors. Characterisation of purified virus assessed by electron microscopy and poliacrylamide gel electrophoresis (PAGE) revealed the typical wheel shape structure of rotavirus particles and the presence of the 11 segments of dsRNA arranged in the 4-2-3-2 pattern. Presence of rotavirus structural proteins including VP6, VP4 and VP7 from the outer shell, was demonstrated by SDS-PAGE and Western blot using polyclonal and VP6-specific monoclonal antibodies. This method achieved a approximately 1500 fold purification, which retained approximately 80% infectivity depending on the concentration protocol used, while yielding 160 microg of viral protein per each litre of infected cell culture medium. The time required for the isopycnic centrifugation was only 25 min and the entire completion of the method required 3.5 h. The method is simple technically and applicable to the purification of large as well as minute amounts of virus.

Incidence and prevalence of human group C rotavirus infections in Argentina

The incidence of human group C rotavirus infections among children and adults in Buenos Aires was evaluated by enzyme linked immunosorbent assays (ELISA) based on recombinant group C VP6 protein (Cowden strain). A total of 976 stool samples taken from patients (ages 6 months to 15 years) with acute diarrhea were tested for the presence of group C rotavirus. Among these, only 10 (1.02%) were group C rotavirus positive by enzyme-linked immunosorbent assay (ELISA) confirmed by absorption with group C VP6 antibodies and by RT-PCR for both VP6 and VP7 genes. The average age (5.86 years) was significantly superior to that in group A-infected patients (1.63 years). Previous exposure to this virus was assessed by detecting specific IgG in sera taken from healthy individuals grouped by age. Of 844 sera tested, 425 (50.3%) were group C IgG positive by ELISA, confirmed by Western blot analysis. The rates of IgG positivity for group A and C rotaviruses during the first years of life indicated that infections with group C are frequent in older children (3-5 years), whereas group A infections are prevalent in infants and young children (6-18 months). This study shows that group C rotavirus infections in Argentine children occur later in life than group A and are relatively common in spite of the low detection rate of this virus.

Characterization of human group C rotavirus in Argentina

A survey was conducted for identification of human group C rotaviruses in stool specimens taken from children suffering diarrhea in suburban Buenos Aires regions. Among 90 true negative group A samples as defined by ELISA, RT-PCR and PAGE, five were positive by group C specific RT-PCR (VP7 and VP6 genes) and three of these samples exhibited the characteristic 4-3-2-2 dsRNA pattern of group C rotavirus. These results were further confirmed by electron microscopy and by ELISA for detection of group C VP6 specific antigens. Sequence analysis of the VP7 gene from one of these isolates revealed a 97.3-98.6% nucleotide identity and up to 99.1% protein homology with human group C rotavirus strains found scattered throughout the last ten years in other countries. Conversely, similar analysis performed with porcine strains showed a much lower homology degree both at the nucleotide (75.5% nucleotide identity) and amino acid level (85.5% protein homology). Detection of group C rotavirus in children with acute diarrhea in Argentina extends the identification range of this agent in the region and is consistent with previous reported data that demonstrate a global distribution of this virus.

VP7 and VP4 genotyping of human group A rotavirus in Buenos Aires, Argentina

Specific and sensitive tests for the detection and typing of group A rotavirus strains are needed for a more comprehensive knowledge of the epidemiology of rotaviral infection. In this study 500 stool specimens taken from 1996 to 1998 from children with acute diarrhea in Buenos Aires were examined. Group A rotavirus was unequivocally demonstrated in 62% of the samples tested by enzyme-linked immunosorbent assay (ELISA) for detection of VP6 antigen, polyacrylamide gel electrophoresis of double-stranded RNA, and reverse transcription-PCR (RT-PCR) for amplification of the VP7:G (1, 062 bp) and VP4:P (876 bp) genes. Only five positive specimens were found by RT-PCR but not by ELISA. G and P typing was carried out by nested amplification of variable sequences of the VP7 and the VP4 genes with six G- and five P-type-specific primers (multiplex PCR). Results obtained by this method showed the prevalence of the following G and P types: G1, 39%; G2, 43%; G4, 4%; P[8], 16%; P[4], 71%. Unexpectedly, the G-P type combination most frequently found was G2P[4] (43%) rather than G1P[8] (12%), which is the most commonly found worldwide. Unusual strains of the type G1P[4] accounted for 14% of the total, while mixed infections with more than one type were found in 10% of the samples. Detection of fecal rotavirus-specific immunoglobulin M (IgM) and IgA antibodies in consecutive samples of two patients taken at daily intervals demonstrated that high levels of IgM and IgA antibodies were detected on day 1 after the onset of disease and that the samples remained positive for about 10 days, after which virus shedding was no longer observed. Multiplex PCR offers a sensitive and specific alternative to determine the prevalence of group A rotavirus G and P types and to identify the emergence of uncommon strains, whereas detection of fecal IgM and IgA antibodies represents a useful supplement to virus detection for the diagnosis of current or recently acquired infections.

Secretory IgM and IgA antibodies to respiratory syncytial virus in nasopharyngeal aspirates: a diagnostic supplement to antigen detection

BACKGROUND

RSV-shedding during an RSV-infection declines dramatically after the first week of infection. It could be of interest to be able to diagnose RSV-infection for a longer period of time by detection of specific RSV-IgM and RSV-IgA in nasopharyngeal aspirates (NPA) in order to minimize unnecessary antibiotics.

OBJECTIVES

To evaluate an ELISA to detect specific RSV-IgM and RSV-IgA in NPA as a supplement to RSV-antigen detection.

STUDY DESIGN

A total of 104 NPA from 101 children (median age 9 months) with acute respiratory disease (group 1) admitted to hospital and consecutive NPA (collected on day 0, 7, 14, 30 and 60) from 11 children (median age 3 months) with a proven RSV infection (group 2) were collected. All NPA from group 1 were analysed for RSV-antigen, RSV-IgM and RSV-IgA. NPA from group 2 were analysed for RSV-IgM and RSV-IgA.

RESULTS

Thirty-five NPA in group 1 were positive for RSV-antigen and 64 were positive for RSV-antigen test alone found 44% and the RSV-IgM test alone found 80%. In group 2 8/11 (73%) has an excellent RSV-IgM response day 7, the rest responded later. Only 5/11 (46%) had a less pronounced RSV-IgA response on day 7, three cases responded later and three did not respond at all. RSV-IgM disappeared in 8/11 (73%) and RSV-IgA in 7/8 (88%) between day 30-60.

CONCLUSIONS

Specific RSV-IgM is a valuable supplement to RSV-antigen detection for the diagnosis of acute and recent RSV infection.

Monoclonal antibodies for the direct detection of influenza-A virus by ELISA in clinical specimens from patients with respiratory infections

BACKGROUND

Monoclonal antibody technology provides antibody reagents of known specificity, high titres and unlimited availability, that form ideal reference antibodies for use in specific viral antigen-detection methods.

OBJECTIVES

To produce mouse monoclonal antibodies against antigenic sites of influenza-A virus, and evaluate their use as diagnostic reagents in a sandwich ELISA.

STUDY DESIGN

(1) Production and characterization of monoclonal antibodies against influenza-A virus; (2) application of these antibodies in an ELISA method for direct antigen detection; and (3) evaluation of the ELISA as routine procedure.

RESULTS

Four monoclonal antibodies (A1-A4) from mice immunized intranasally with influenza-A virus were selected according to their specific reactivity with either nucleoprotein or matrix protein antigens as demonstrated by Western blot analysis. These antibodies lacked haemagglutination inhibition and neutralization properties and recognized both H1N1 and H3N2 strains of influenza-A virus equally. A sandwich ELISA using unlabelled antibodies for antigen capture and biotin-labelled antibodies for antigen detection was used to analyse nasopharyngeal secretions or nasal swabs from culture-confirmed influenza-A-infected patients and comparable specimens from patients with other viral respiratory infections. Only influenza-A virus (strains H1N1 and H3N2) could be detected in samples from patients with known influenza-A and influenza-B infections, and also after re-isolation of such viruses in conventional cultures of MDCK cells or embryonated hens' eggs. The antigen-detection assay showed a diagnostic sensitivity of 100% and a specificity of 98.3% compared with conventional culture methods.

CONCLUSION

The reported ELISA appears to be a rapid and inexpensive method for diagnosis and epidemiological studies of influenza-A infections.

Relationship between viral antibodies and bronchial hyperresponsiveness in 495 unselected children and adolescents

The purpose of this study was to investigate whether recent and previous subclinical viral respiratory infection can explain the presence of increased bronchial responsiveness to histamine. We studied a randomly selected population of 495 children and adolescents, aged 7-16 years, from Copenhagen. If the subjects had had symptoms of respiratory infection recently, the examination was postponed for at least 6 weeks. Bronchial hyperresponsiveness (BHR) to inhaled histamine was found in 79 (16%) of the subjects, of whom 28 had asthma. Forty-eight subjects (10%) had increased levels of serum IgM antibodies against either parainfluenza, influenza, adenovirus, or respiratory syncytial virus (RSV), reflecting a recently acquired infection. No association between BHR and antibodies against respiratory viruses was found, as 7 (8.9%) of the 79 subjects with BHR and 41 (9.9%) of the 416 subjects without BHR had viral antibodies. Furthermore, no association between degree of bronchial responsiveness and viral antibodies was found. Moreover, 251 individuals (51%) had signs of earlier RSV infection, i.e. IgG antibodies against RSV. No relationship was found between age of the subjects and the presence of antibodies against either respiratory viruses in general or IgG-RSV. No relationship was found between the presence of antibodies against RSV and BHR; furthermore, evidence of earlier RSV infection was unrelated to the level of lung function and degree of bronchial responsiveness. We conclude that increased bronchial responsiveness in asymptomatic, unselected schoolchildren and adolescents is not likely to be caused by recent or previous viral respiratory infections.

Subclinical measles infection in vaccinated seropositive individuals in arctic Greenland

Measles vaccination was performed in the arctic district of Scoresbysund, Greenland in 1968, which had never been exposed to natural measles. More than 90% of the total population was vaccinated and a 94-100% seroconversion was obtained. During a serological survey to examine the immunity status of the vaccinees, it was discovered that a temporary increase in measles antibodies took place in the majority of the population 2-4 years after the vaccination. This was not accompanied by clinically observed measles. Most likely, it was due to an inapparent measles infection in a population considered highly immune after vaccination.

Prevalence of IgG-antibodies to mumps and measles virus in non-vaccinated children

The prevalence of mumps and measles IgG antibodies in a randomly selected population of children was determined by an enzyme-linked immunosorbent assay (ELISA) before routine measles-mumps-rubella (MMR) vaccination was introduced in Denmark. Testing of sera from about 2,520 Danish children between one and 17 years of age showed that mumps antibodies were acquired at an early age. The peak acquisition rate was between the ages of four and five; before the age of 15, 90% of children had antibodies to mumps. Immunity to measles occurred at an even earlier age; more than 50% of four-year-old and nearly all (98%) nine-year-old children had IgG antibodies to measles virus. The study showed that about 10% of the young adult Danish population was still susceptible to mumps infection whereas only about 1% of individuals at age 17 had not acquired immunity to measles virus.

Intratypic differentiation of poliovirus strains by enzyme-linked immunosorbent assay (ELISA): poliovirus type 2 and poliovirus type 3

A double-antibody sandwich ELISA was developed for the detection of antigenic differences between wild and vaccine-derived strains of poliovirus type 2 and poliovirus type 3. Antibodies were prepared in rabbits by immunization with purified antigens of vaccine strains (type 2: Sabin P712, and type 3: Sabin Leon) and wild type strains (type 2: MEF, and type 3: Pool 30). Immunoblotting analysis of all antisera demonstrated that the IgG antibodies raised in rabbits have specificity towards the main structural proteins (Vp1, Vp2 and Vp3) of poliovirus. IgG fractions were purified from antisera by affinity chromatography, on a protein A-activated Sepharose 4B column. Purified IgG antibodies were used for coating of microtest plates (catching antibodies). The same reagents labelled with horseradish peroxidase were used as conjugates, after cross-adsorption with antigens of the same type heterologous virus strains (strain-specific conjugates). 29 poliovirus type 2 strains and 73 poliovirus type 3 strains isolated from clinical samples, were differentiated intratypically, as vaccine-derived or wild types, no intermediate strains were found and all samples tested fell in two distinct (vaccine/wild) categories. As little as 40 ng of poliovirus antigens was detected in stool samples from healthy children or from polio patients cultivated in monkey kidney tissue cultures. Preparation of strain specific conjugates did not require large amounts of poliovirus antigens. The developed ELISA, which is economic and capable of (1) detection of low amounts of poliovirus antigens in cultivated clinical samples, and (2) intratypic differentiation of poliovirus antigens as either vaccine-derived or wild type, is therefore well suited for large scale screening of poliovirus isolates.

Detection of specific immunoglobulin M to mumps virus in serum and cerebrospinal fluid samples from patients with acute mumps infection, using an antibody-capture enzyme immunoassay

An immunoglobulin M (IgM) antibody-capture immunoassay using peroxidase-labelled mumps antibodies is described and its suitability for the practical diagnosis of acute mumps infection is evaluated. All 45 patients with confirmed mumps infection showed specific mumps IgM antibodies in their sera. Similarly, mumps IgM antibodies were detected in cerebrospinal fluid samples and sera from 12 patients with meningitis. Among these patients 8 had positive mumps virus isolates from the cerebrospinal fluid and 4 had not. Conversely, mumps IgM antibodies were detected neither in 418 serum samples from adult patients expected to be negative for mumps IgM, nor in 184 cerebrospinal fluid specimens from patients with various central nervous system symptoms, nor in sera from 10 patients with high levels of IgM-rheumatoid factor. Among 20 patients with respiratory illness caused by parainfluenza type-1 virus none showed an IgM mumps antibody response. In 99% of cases with acute mumps infection the IgM-ELISA gave a positive result in the first available serum samples most of which were negative for CF and mumps IgG antibodies. The virus proteins which take part in the IgM-ELISA test immune reaction are mainly the nucleoprotein and to a lesser extent the membrane protein. The IgM-ELISA method, which can be performed in 6 hours, offers a reliable, sensitive and rapid alternative to routine methods for the diagnosis of acute mumps infection.

Serological diagnosis of mumps and parainfluenza type-1 virus infections by enzyme immunoassay, with a comparison of two different approaches for detection of mumps IgG antibodies

Two solid-phase enzyme-linked immunosorbent assays (ELISA) for detection of mumps IgG antibodies, viz., indirect ELISA and catching-antibodies (C.A.)-ELISA, are described and the results obtained with both assays are compared with each other and with the conventional complement-fixation (CF) test. In the indirect method, mumps antigens are used for coating the wells of the microtest plates, whereas in the C.A.-ELISA method mumps antigens are selectively bound to rabbit anti-mumps antibodies coated surfaces. A positive correlation was found between the optical density (O.D.) values given by both ELISA assays and CF-antibody titers. The ELISA assays showed improved sensitivity compared to the CF test, since 54% (C.A.-ELISA) and 33% (Indirect-ELISA) of additional positive reactions were detected by these assays. In terms of specificity, however, only the C.A.-ELISA was superior to CF, since significant rises of IgG-antibodies were detected only in paired sera of mumps patients. Conversely, when the indirect method was used significant IgG antibody rises were demonstrated in paired sera from mumps patients and in serum pairs of six patients with parainfluenza type-1 virus infection. With the CF test, heterologous antibodies responses were demonstrated in 2 of these patients. Absorption experiments of mumps sera with mumps and parainfluenza virus strains demonstrated that the IgG antibodies detected by the C.A.-ELISA are specific for mumps virus and therefore interference due to heterologous antibody responses were not observed. Results with purified mumps virus proteins demonstrated that the antigen-antibody reactions that partake in the C.A.-ELISA are mainly associated with the nucleoprotein antigen. Detection of IgG-antibodies to parainfluenza virus type-1 was assessed by ELISA (paraflu-T1-ELISA) using only the indirect approach. The results obtained with this assay showed improved sensitivity compared to a paraflu T1-CF test, since 47% of additional positive reactions were demonstrated by ELISA. In terms of specificity, however, heterologous antibody responses were detected by both the ELISA and the CF test in 4 out of 20 patients with mumps infections.

High incidence of beta-2-microglobulin containing macromolecular complexes in sarcoidosis sera

In thirteen out of fourteen sarcoidosis patients with elevated serum levels of immune complexes beta-2-microglobulin (beta 2m) was detected in immune complex-enriched fractions prepared by precipitation with 3% polyethylene glycol. Beta-2-microglobulin was also contained in complexes isolated by means of solid-phase Clq. The levels of free beta 2m in sarcoidosis sera did not differ from the concentrations in sera from healthy donors.

Estimation of immune complexes by a microplate-adapted C1q-Protein A enzyme-linked-immunosorbent-assay (C1q-PA-ELISA)

A microplate-adapted enzyme linked immunosorbent assay (ELISA) for detection of C1q-binding immune complexes (IC) and aggregated IgG (delta IgG) is described. Purified human C1q was adsorbed to the wells of flat-bottomed microtiter plates and EDTA-treated serum samples were subsequently introduced. Bound IC was measured by use of alkaline phosphatase-labelled Protein A followed by the substrate para-nitro-phenyl-phosphate. A dose response was found for both delta IgG and BSA anti-BSA complexes, while variations in the concentration of monomer IgG did not affect the optical density. Elevated levels of IC were found in the majority of sera from patients with rheumatoid arthritis and SLE. The described C1q-PA-ELISA is a simple and inexpensive method for detection of C1q-binding immune complexes. The reproducibility is acceptable and the sensitivity is higher than for most IC-methods based on C1q-binding.

Beta2-microglobulin-containing IgG complexes in sera and synovial fluids of rheumatoid arthritis and systemic lupus erythematosus patients

The occurrence and composition of complexed beta2-microglobulin (beta2m) in sera and synovial fluids of rheumatoid arthritis and systemic lupus erythematosus patients and control persons was investigated. Beta2m-containing complexes were detected in immune complex (IC)-enriched fractions isolated by precipitation with 3% polyethylene glycol 6000, in the macromolecular peaks after Sephadex G-200 gel filtration, and in IC desorbed from solid-phase Clq. Beta2m complexes were demonstrated also after precipitation of redissolved PEG-insoluble material by anti-human beta2m serum or isolation of the complexes by use of Sephadex-anti-beta2m. IgG was co-isolated with beta2m on Sephadex-anti-beta2m and free beta2m inhibited the binding of IgG to Sephadex anti-beta2m, indicating that IgG was present in the complexed beta2m. Analysis by SDS-polyacrylamide gradient electrophoresis under reducing conditions indicated that the purified beta2m complexes contained IgG and beta2m.

Soluble immune complexes in cerebrospinal fluid of patients with multiple sclerosis and other neurological diseases

The occurrence of soluble immune complexes (IC) in the cerebrospinal fluid (CSF) of 14 multiple sclerosis (MS) patients, four acute polyradiculoneuritis patients, 30 patients with other neurological diseases (OND) and 30 patients with disc prolapse (DP) was examined by a solid phase C1q-protein A binding assay (C1q-PABA) and a complement consumption test. IC-positive reactions were observed only in the C1q-PABA. The binding indices determined by the C1q-PABA differed significantly (P < 0.01) when the MS or the OND patient groups were compared to the DP group. No significant (P < 0.1) difference was observed between the indices in the MS and OND groups. Binding indices in C1q-PABA showed no correlation either to IgG concentration, total protein concentration or cell counts in CSF of MS patients. Three of the four polyradiculoneuritis patients were strongly IC-positive while the fourth patient was negative. Filtration and PEG-precipitation data indicated that a major part of the IgG-containing IC in CSF detected by C1q-PABA was of macromolecular nature.

Circulating immune complexes, free antigen and alpha 1-antitrypsin in levels in sarcoidosis patients

Consecutive serum samples from 26 sarcoidosis patients were examined for circulating immune complex (IC) activity. Fifteen (58%) gave IC-positive reactions in a complement consumption (CC) test and a significant difference as regards anticomplementary was observed when comparing patients in clinical stages 2 and 1 respectively (P less than 0.01) The serum alpha 1-antitrypsin levels were not correlated (r=0.36) to the results of the CC-assay. The duration of IC-occurrence was studied, by two IC-assays, over 1 1/2 to 2 years. The majority of the positive reactions were registered in patients in clinical stage 2. Isolated IC was used for immunization of rabbits. Absorbed immune sera produced a single precipitate of postalbumin mobility with seven out of 36 sarcoidosis sera. In two cases a tailing of the recipitate suggested that the antigen was in complex formation. Immunoelectrophoresis indicated identity between the antigen detected in different sarcoidosis sera. No precipitates were observed using 130 sera from other patients, and screening of 100 blood donors revealed one positive reaction. The antigen, which eluted in the first protein peak on Sephadex G-200, has not been identified serologically.

Immune complexes in the sputum of patients with cystic fibrosis suffering from chronic Pseudomonas aeruginosa lung infection

12 cystic fibrosis (CF) patients chronically infected with mucoid P. aeruginosa and presenting multiple precipitins in serum against this bacterium and 12 patients without P. aeruginosa infection were examined for occurrence of soluble immune complexes in their sputum sol phase by a complement consumption assay and a solid phase rheumatoid factor binding assay. The correlation between the results obtained in the two assays was significant (r = 0.625, p less than 0.01). The patients chronically infected with P. aeruginosa showed a significantly (p less than 0.01) higher frequency of immune complex activity in their sputum sol phase, as compared to the patients without P. aeruginosa lung infection. These findings point to the possibility that chronic lung infection with mucoid P. aeruginosa in CF may be an immune complex disease.