Viral antibody screening system that uses a standardized single dilution immunoglobulin G enzyme immunoassay with multiple antigens

Compensating for cross-reactions using avidity and computation in a suspension multiplex immunoassay for serotyping of Zika versus other flavivirus infections

The recent spread of Zika virus (ZIKV) in the Americas and Asia necessitates an increased preparedness for improved maternal and perinatal health and blood safety. However, serological cross-reactions, especially to Dengue virus (DENV), complicate ZIKV antibody serodiagnosis. A novel “pan-Flavi” suspension multiplex immunoassay (PFSMIA) using 25 antigens, whole virus (WV), non-structural protein 1 (NS1), and envelope (E) proteins, from 7 zoonotic flaviviruses for specific detection of ZIKV and DENV IgM and IgG was developed. Patterns of antibody cross-reactivity, avidity, and kinetics were established in 104 sera from returning travelers with known ZIKV and DENV infections. PFSMIA gave IgM- and IgG-sensitivities for both viruses of 96–100%, compared to an immunofluorescence assay. Main IgM cross-reactions were to NS1, for IgG to the E and WV antigens. Infecting virus yielded reactivity to several antigens of the homologous virus, while cross-reactions tended to occur only to a single antigen from heterologous virus(es). A specificity-enhancing computer procedure took into account antibody isotype, number of antibody-reactive antigens per virus, avidity, average degree of cross-reactivity to heterologous flavivirus antigens, and reactivity changes in serial sera. It classified all 50 cases correctly. Applied to sera from 200 pregnant women and 173 blood donors from Sweden, one blood donor was found ZIKV NS1 IgM positive, and another as ZIKV NS1 IgG positive. These samples did not react with other ZIKV antigens and were thereby judged as false-positives. PFSMIA provided sensitive and specific ZIKV and DENV serology, warranting high-throughput serological surveillance and a minimized need for laborious and expensive virus neutralization assays.

Epitopes of microbial and human heat shock protein 60 and their recognition in myalgic encephalomyelitis

Myalgic encephalomyelitis (ME, also called Chronic Fatigue Syndrome), a common disease with chronic fatigability, cognitive dysfunction and myalgia of unknown etiology, often starts with an infection. The chaperonin human heat shock protein 60 (HSP60) occurs in mitochondria and in bacteria, is highly conserved, antigenic and a major autoantigen. The anti-HSP60 humoral (IgG and IgM) immune response was studied in 69 ME patients and 76 blood donors (BD) (the Training set) with recombinant human and E coli HSP60, and 136 30-mer overlapping and targeted peptides from HSP60 of humans, Chlamydia, Mycoplasma and 26 other species in a multiplex suspension array. Peptides from HSP60 helix I had a chaperonin-like activity, but these and other HSP60 peptides also bound IgG and IgM with an ME preference, theoretically indicating a competition between HSP60 function and antibody binding. A HSP60-based panel of 25 antigens was selected. When evaluated with 61 other ME and 399 non-ME samples (331 BD, 20 Multiple Sclerosis and 48 Systemic Lupus Erythematosus patients), a peptide from Chlamydia pneumoniae HSP60 detected IgM in 15 of 61 (24%) of ME, and in 1 of 399 non-ME at a high cutoff (p<0.0001). IgM to specific cross-reactive epitopes of human and microbial HSP60 occurs in a subset of ME, compatible with infection-induced autoimmunity.

No evidence for xenotropic murine leukemia-related virus infection in Sweden using internally controlled multiepitope suspension array serology

Many syndromes have a large number of differential diagnoses, a situation which calls for multiplex diagnostic systems. Myalgic encephalomyelitis (ME), also named chronic fatigue syndrome (CFS), is a common disease of unknown etiology. A mouse retrovirus, xenotropic murine leukemia-related virus (XMRV), was found in ME/CFS patients and blood donors, but this was not corroborated. However, the paucity of serological investigations on XMRV in humans prompted us to develop a serological assay which cover many aspects of XMRV antigenicity. It is a novel suspension array method, using a multiplex IgG assay with nine recombinant proteins from the env and gag genes of XMRV and 38 peptides based on known epitopes of vertebrate gammaretroviruses. IgG antibodies were sought in 520 blood donors and 85 ME/CFS patients and in positive- and negative-control sera from animals. We found no differences in seroreactivity between blood donors and ME/CFS patients for any of the antigens. This did not support an association between ME/CFS and XMRV infection. The multiplex serological system had several advantages: (i) biotinylated protein G allowed us to run both human and animal sera, which is essential because of a lack of XMRV-positive humans; (ii) a novel quality control was a pan-peptide positive-control rabbit serum; and (iii) synthetic XMRV Gag peptides with degenerate positions covering most of the variation of murine leukemia-like viruses did not give higher background than nondegenerate analogs. The principle may be used for creation of variant tolerant peptide serologies. Thus, our system allows rational large-scale serological assays with built-in quality control.

Impact ofHelicobacter pyloriInfection on the Humoral Immune Response to MUC1 Peptide in Patients with Chronic Gastric Diseases and Gastric Cancer

Many investigators have demonstrated alteration of gastric mucins in H. pylori infected individuals. The inflammatory environment induced by H. pylori leading to aberrant glycosylation of MUC1 and demasking of core peptide MUC1 epitope could enhance immune responses to MUC1. IgG and IgM immune response to MUC1 in patients with gastric cancer (n = 214) chronic gastroduodenal diseases (n = 160) and healthy blood donors (n = 91) was studied with ELISA using bovine serum albumin-MUC1 60-mer peptide as antigen. H. pylori serologic status was evaluated with ELISA and CagA status by immunoblotting. Gastric mucosa histology was scored according to the Sydney system. Compared to H. pylori seronegative individuals, higher levels of IgG antibody to MUC1 were found in H. pylori seropositive patients with benign gastric diseases (p < 0.01) and blood donors (p < 0.03). Higher MUC1 IgG antibody levels were associated with a higher degree of gastric corpus mucosa inflammation in patients with chronic gastroduodenal diseases (p < 0.0025). There was a positive correlation between the levels of anti-H. pylori IgG and MUC1 IgG antibody levels in blood donors (p = 0.03), and in patients with benign diseases (p < 0.0001). In patients with gastric cancer (n = 214) a significantly higher level of anti-MUC1 IgG than in blood donors was observed (p < 0.001) irrespective of H. pylori status or stage of cancer. MUC1 IgM antibody levels were not related to the H. pylori serology. IgG immune response to tumor-associated MUC1 is up regulated in H. pylori infected individuals. This increase is associated with a higher IgG immune response to H. pylori and with a higher degree of gastric mucosa inflammation. High levels of MUC1 IgG antibody irrespective of H. pylori serologic status characterized patients with gastric cancer. The findings suggest that, in some individuals, the H. pylori infection may stimulate immune response to tumor-associated MUC1 peptide antigen thus modulating tumor immunity.

Quantitative PCR-enhanced immunoassay for measurement of enteroviral immunoglobulin M antibody and diagnosis of aseptic meningitis

A PCR-enhanced immunoassay (PIA) to detect enterovirus (EV) immunoglobulin M (IgM) for diagnosis of recent EV infection was recently developed. This test was compared with another EV IgM capture technique, the solid-phase reverse immunosorbent test (SPRIST). Fourteen of 43 serum samples from aseptic meningitis patients were positive by PIA, whereas 10 were positive by SPRIST. One of 39 control serum samples was weakly positive by PIA. A single-serum-dilution real-time PCR-based PIA for EV IgM (quantitative PIA [QPIA]) was also developed and evaluated against PIA, SPRIST, an EV IgM radioimmunoassay (RIA), and clinical data. A mixture of 12 EVs was used as the antigen. Results from investigating four groups of serum samples were as follows. (i) The nine PIA-positive serum samples in group 1 were all positive by QPIA. (ii) Group 2 consisted of 59 serum samples from aseptic meningitis patients. Nineteen of 30 serum samples (63%) taken at hospital admission were positive by QPIA. Of these, 17 were positive in EV PCR. (iii) None of the 30 control serum samples in group 3 were positive by QPIA. (iv) For the 24 serum samples in group 4, of which 11 were positive and 13 were negative by RIA, the QPIA results were completely concordant. The sensitivity and specificity of QPIA for diagnosis of EV infection were 70 and 80%, respectively. QPIA provides a rational strategy for the detection of EV IgM, allows the use of viral antigens with minimal purification, and needs no virus-specific reagents apart from those in the PCR. QPIA is a generally applicable method for the detection of viral IgM in IgM capture assays.

Expression of tumor-associated Thomsen-Friedenreich antigen (T Ag) in Helicobacter pylori and modulation of T Ag specific immune response in infected individuals

We tested the hypothesis that the gastric cancer associated bacteria, Helicobacter pylori (H. pylori) express the cancer-related Thomsen-Friedenreich (T) antigen. We also analysed whether infection with H. pylori alters the amount of natural anti-T antibodies in the patients' sera. Cell surface membrane extracts of H. pylori NCTC 11637 strain and clinical isolates of H. pylori (n = 13) were analysed by immunoblotting and cell-ELISA with five different T antigen-specific monoclonal antibodies (MAbs). Two major protein bands of approximately 68 kDa and 58 kDa were immunostained on blots of H. pylori extracts with T specific MAbs but not immunostained with unrelated MAb. The specificity was shown in that immunostaining was blocked with peanut agglutinin (PNA) and rabbit antiserum to T antigen. The binding of T specific MAb to the 58 kDa protein band was also blocked by rabbit antiserum against heat shock proteins of H. pylori. The relative expression of T antigen-related proteins differed among H. pylori strains, with 68 kD associated T antigen expression higher in patients with more severe pathology. The level of IgG antibody to T epitope in patients with gastric cancer (n = 66) and normal blood donors (n = 62) were compared and the level of anti-T Ab in gastric cancer patients was significantly lower than that in normal blood donors. A significant positive correlation between T specific antibody in serum and H. pylori IgG antibody level was found in H. pylori-infected normal blood donors (P < 0.001), but this correlation was not found in H. pylori-infected cancer patients. In summary, the cancer related T epitope is expressed in H. pylori and modulation of T antigen-specific immune response in H. pylori-infected individuals suggests that H. pylori infection may alter natural immune mechanisms against cancer.

Prospective study of etiologic agents of community-acquired pneumonia in patients with HIV infection

OBJECTIVES

To study prospectively HIV-positive patients admitted to the hospital because of pneumonia by extensive laboratory tests to determine specific microbiologic diagnoses and to establish the best clinical diagnosis after review of all available data by expert clinicians.

METHODS

Patients admitted to one of two hospitals had extensive questionnaires completed and defined diagnostic tests performed on blood, sputum, urine and bronchoalveolar lavage specimens, when available.

RESULTS

A total of 230 patients had a diagnosis of pneumonia verified. A definite or probable etiologic diagnosis was made in 155 (67%) of these patients. Pneumocystis carinii caused 35% of all cases of pneumonia. Twenty-seven percent of cases of pneumonia with a single etiology had a definite or probable bacterial etiology. 'Atypical agents' were distinctly uncommon. Few clinical or laboratory parameters could differentiate specific etiologies.

CONCLUSIONS

P. carinii continues to be a common cause of pneumonia in these patients. The rarity of 'atypical agents' could simplify the empiric approach to therapy. Despite the use of extensive testing we did not find a definite etiology in a large number of cases.

A novel serological technique: polymerase chain reaction enhanced immunoassay. Application to enterovirus IgM diagnosis

The polymerase chain reaction (PCR) method is a sensitive, specific and rapid technique for virus detection. The principles of a PCR enhanced immunoassay (PIA) are described. The method combines solid phase serological techniques with the PCR, providing a versatile and sensitive method for antibody detection. By linking the antigenicity of virus particles with their content of nucleic acid, the method provides new possibilities for virus serology: for example, antibody specificity can be coupled to viral sequence in patients with chronic infections caused by highly variable viruses such as HIV and HCV. An application of the PIA technique is described for the detection of anti-enterovirus IgM. IgM is captured to anti-human IgM-coated microwell plates. The anti-enterovirus IgM is allowed to bind crude enterovirus antigen. Bound virus is heat denatured and the released RNA is used as a template for reverse transcription PCR (RT-PCR) amplification. Amplicons are detected by hybridisation to an affinity labelled probe in a microwell colorimetric assay. In a pilot study, 18 serum specimens from patients with enterovirus infections were examined. Using a mixture of ten crude enterovirus antigens, the frequency of IgM positivity was 6/18 (33%). Titres between 1/500 and 1/100,000 were recorded. Predominantly type-specific antibodies were detected. The results were compared with a procapsid enterovirus radioimmunoassay (RIA). After further optimisation, the PIA has the potential to be a clinically useful assay for the detection of antiviral antibodies.

Standardization of enzyme-linked immunosorbent assays (ELISAs) for quantitative estimation of antibodies specific for infectious bovine rhinotracheitis virus, respiratory syncytial virus, parainfluenza-3 virus, and bovine viral diarrhea virus

Commercial enzyme-linked immunosorbent assays (ELISAs) for detection of serum antibodies to bovine viral diarrhea virus (BVDV), parainfluenza-3 virus (PI3V), respiratory syncytial virus (RSV), and infectious bovine rhinotracheitis virus (IBRV) were standardized to give a quantitative result when testing was performed at a single optimum dilution. For each test, serum samples were titrated and their end point titers calculated by an algebraic method directly from a plot of each titration series and also from a regression line fitted to this plot. The corrected optical density (COD) of each sample when tested at dilutions of 1/25, 1/50, and 1/100 was expressed as a percentage of the COD of a positive reference serum included on each plate, this value was the sample/positive (S/P) ratio. For each test, the linear relationship between the S/P ratio obtained at a dilution of 1/25, 1/50, and 1/100 and the end point titer calculated by each method was determined. In each case, the best linear relationship existed when samples were tested at a dilution of 1/100 (r = 0.973 for BVDV, 0.962 for PI3V, 0.961 for RSV, 0.947 for IBRV). From the equation of these lines, an increase in the S/P ratio between acute and convalescent serum samples of 31%, 23%, 21%, and 35% would correspond to a 4-fold rise in ELISA titer to BVDV, PI3V, RSV, and IBRV, respectively. ELISA titers calculated from S/P ratios at 1/100 were significantly related to virus neutralization titers to BVDV, RSV, and IBRV and to hemagglutination inhibition titers to PI3V (P < < 0.001 in all cases). Samples with low S/P ratios had the greatest intraassay and interassay variation. Intraassay reproducibility ranged from 3.5% to 22.3% (coefficient of variation), with a median value of 9.5%. Interassay reproducibility was lower, ranging from 6.0% to 50.6%, with a median of 17.4%.

Selective antibody reactivity with peptides from human endogenous retroviruses and nonviral poly(amino acids) in patients with systemic lupus erythematosus

OBJECTIVE

To investigate antibody responses to a broad panel of peptides derived from human endogenous retroviruses (HERVs) among unselected patients with systemic lupus erythematosus (SLE).

METHODS

In sera obtained from 69 patients with SLE and healthy blood donors, immunoassay was used to measure levels of antibody against synthetic peptides derived from HERVs, exogenous retroviruses, and nonviral poly(amino acids).

RESULTS

Measurement by immunoassay revealed increased frequencies of antiretroviral antibodies against 2 peptides derived from the env gene of the type C-like class, which includes ERV-9 and HERV-H, and against 2 peptides from the gag region of human T lymphotropic virus type I-related endogenous sequence 1, in patients with SLE. Antibodies to 2 nonviral peptides, polyhistidine and polyproline, were also overrepresented in patient sera. In 1 patient, longitudinal data obtained over a period of 12 years indicated that the concentrations of certain antiretroviral antibodies varied according to disease activity.

CONCLUSION

Reactivity to certain type C HERV-derived antigens was found among patients with SLE. This reactivity could be explained by increased exposure to cross-reactive epitopes from essentially complete type C HERVs.

Increased antiretroviral antibody reactivity in sera from a defined population of patients with systemic lupus erythematosus. Correlation with autoantibodies and clinical manifestations

OBJECTIVE

The implied role of retroviruses in the pathogenesis of murine systemic lupus erythematosus (SLE) led us to study antiretroviral antibodies in a population-based SLE cohort.

METHODS

Immunoassays using whole virus and synthetic peptides were performed on sera from 72 patients with SLE and 88 control subjects.

RESULTS

Reactions with whole baboon endogenous virus occurred more frequently in patients with SLE, and correlated with the presence of anti-RNP and anti-Sm. Some retroviral env and gag peptides, several of which were similar to U1 small nuclear RNP, reacted more strongly in patients with SLE, and their presence was correlated with discoid rash, hematologic disorder, and other symptoms.

CONCLUSION

These results provide circumstantial evidence for involvement of retroviruses in the pathogenesis of human SLE; further studies should be carried out using other techniques for measurement of retroviral expression.

Levels of immunoglobulin G antibodies against defined epitopes of the L1 and L2 capsid proteins of human papillomavirus type 6 are elevated in men with a history of condylomata acuminata

Sera from 159 men attending the sexually transmitted disease clinic at Karolinska Hospital, Stockholm, Sweden, were analyzed for the presence of immunoglobulin A (IgA) and IgG antibodies to a panel of synthetic peptides derived from the E2, L1, and L2 regions of the human papillomavirus types 1 (HPV 1), 6, 8, 11, 16, 18, 31, and 33. The study subjects were divided into three groups: (i) asymptomatic men with no history of genital warts who served as controls, (ii) men with visible condylomata, and (iii) men who had previously been afflicted with condylomata. There were no significant differences in antibody titers for any of the HPV 6- or 11-derived peptides among patients with current condylomata and the controls. For the peptide from L1 of HPV 6, there was an increase in the IgG titers among men with previous condylomata compared with the titers for the controls (52% versus 27% seropositivity; P less than 0.05). Also, for the peptide from L2 of HPV 6, there was an increase in the IgG titers among men who had been afflicted with condylomata previously (P less than 0.05). Increased IgA antibody titers against an HPV 16-derived peptide and an HPV 18-derived peptide were also detected. For the peptides from L1 and L2 of HPV 6, the study was extended to an additional group of 127 males attending the sexually transmitted disease clinic at Huddinge Hospital in southern Stockholm. Again, significantly increased antibody levels were detected only for IgG and only among asymptomatic men with a history of condylomata (P < 0.01 for the L1 peptide and P < 0.05 for the L2 peptide). The results suggest that the IgG response against the late proteins of HPV 6 reflects mainly previous exposure to the virus rather than ongoing viral disease.

Characterization of pseudorabies virus antibody responses in young swine after infection and vaccination by using an immunoglobulin M antibody capture enzyme-linked immunosorbent assay

An immunoglobulin M (IgM) antibody capture enzyme-linked immunosorbent assay (MACELISA) was developed for the detection of pseudorabies virus (PRV)-specific IgM antibody in swine sera because false-positive reactions frequently occurred when sera from older swine were tested with an indirect IgM enzyme-linked immunosorbent assay. Monoclonal mouse anti-swine IgM was used as the capturing antibody, and rabbit anti-PRV hyperimmune gamma globulin was used as the indicating antibody. Sera from non-PRV-infected, experimentally infected, vaccinated and challenged, passively immune and challenged, and naturally infected swine were evaluated. The PRV MACELISA had a specificity of 95% and was as sensitive and reproducible as previously reported in direct assays. An antibody response was still detectable with the MACELISA 21 days after inoculation. The PRV MACELISA did not detect a consistent antibody response in sera from swine vaccinated with either killed-PRV or modified live-virus vaccines but did detect an antibody response in sera from passively immune pigs after challenge with virulent PRV. These results indicated that the PRV MACELISA may be useful for the rapid serodiagnosis of recent PRV infection in swine.

Antigenic and immunogenic epitopes shared by human papillomavirus type 16 and bovine, canine, and avian papillomaviruses

All types of papillomaviruses (PV) share common, so-called group-specific epitopes. To identify the major group-specific epitopes, we immunized 26 guinea pigs or rabbits with purified bovine PV type 1 (BPV), canine PV, or avian PV from the common chaffinch. The resulting hyperimmune sera, as well as a commercially available rabbit antiserum to BPV and seven monoclonal antibodies to BPV, were tested in an enzyme-linked immunosorbent assay with a set of 66 overlapping 20-amino-acid peptides representing the complete sequence of the major capsid proteins (L1 and L2) of human PV type 16 (HPV 16). Sera from the same animals before immunization were used as controls. The minimal reactive epitopes within each peptide were further characterized by testing of truncated peptides. The cross-reactive epitopes were clustered in two regions of L1, an internal region (at positions 171 to 235), which contained three epitopes, and the more reactive region at the carboxy terminus (at positions 411 to 475), which contained six epitopes. The most reactive of the HPV 16 broadly cross-reactive epitopes was a carboxy-terminal epitope which had the sequence DTYRF and which reacted with nine of the antisera to BPV, canine PV, or avian PV, with the commercially available rabbit antiserum to BPV, and also with a mouse monoclonal antibody to BPV. Antipeptide antisera to all of the HPV 16 L1 peptides and to the most antigenically reactive of their truncated analogs were made in guinea pigs. Antipeptide antisera reactive with BPV were obtained for three of the cross-reactive epitopes, and one of these antisera allowed highly sensitive detection of group-specific PV antigen by immunoperoxidase staining.

Serum antibodies against respiratory tract viruses in episodes of acute otitis media

Although the findings of epidemiological studies have suggested viral respiratory tract infection (RTI) to be crucially involved in the development of acute otitis media (AOM), the relationship between AOM and viral RTI remains unclear. Serum samples, obtained in the acute and convalescent phases of 57 AOM episodes (in 35 children during the first three years of life) were analysed for IgG antibodies against influenza A viruses, influenza B viruses, parainfluenza virus type 1, respiratory syncytial virus and adenoviruses. One third of the AOM episodes (18/57) could be related to viral RTI, as evidenced by significant increases in viral serum antibody activity. Treatment failure occurred in four AOM episodes where increases in serum viral antibody activity were noted. In three of these failures, antibiotic treatment was unsuccessful despite the bacterial strains not being resistant to the drug used. This suggests that concomitant viral infection may be a determinant of treatment outcome in some AOM episodes.

Erythromycin and phenoxymethylpenicillin (penicillin V) in the treatment of respiratory tract infections as related to microbiological findings and serum C-reactive protein

Respiratory tract pathogens (beta-haemolytic streptococci groups A, C and G, Haemophilus influenzae, Branhamella catarrhalis or pneumococci), were isolated from nasopharyngeal and/or throat swabs in 73/138 (53%) patients greater than 10 years of age with a clinical diagnosis of acute sinusitis, acute tonsillitis, purulent nasopharyngitis or acute bronchitis. Serological evidence of a viral infection (influenza A and B, parainfluenza 1, 2 and 3, respiratory syncytial virus, adenovirus) or Mycoplasma pneumoniae infection was found in 10% of the patients. The serum content of C-reactive protein (S-CRP) was increased (greater than 12 mg/l) in 26/33 (79%) patients with streptococci and in 22/59 (37%) patients without respiratory tract bacteria. In patients with a serological evidence of a virus tonsillitis, the S-CRP was also high (32-64 mg/l). At follow-up 10-12 days after the first visit, the clinical effect of erythromycin and penicillin V was judged to be similar (90% clinical effect). Relapse or re-infection with group A streptococci were seen in 7 patients (4 on erythromycin, 3 on penicillin). In another 6 patients (3 on erythromycin, 3 on penicillin), antibiotic treatment was switched owing to persisting symptoms, probably due to H. Influenzae infection in 3 cases. The patients' own estimates of their symptoms suggested treatment with erythromycin to have a more rapid effect than treatment with penicillin.

Identification of regions of HIV-1 p24 reactive with sera which give "indeterminate" results in electrophoretic immunoblots with the help of long synthetic peptides

We analyzed nine sera from persons unlikely to be HIV infected which had an IgG reactivity directed against HIV-1 p24, and in two cases also to its precursor p55, but to no other HIV proteins, nor to proteins of the H9 host cell, in electrophoretic immunoblots (EIB). These sera are also referred to as having an indeterminate HIV EIB pattern or as HIV antibody false positive sera. Seven of nine sera reacted with longer (61-77 amino acids) and none with shorter (17-25 amino acids) p24-derived peptides in enzyme immunoassays (EIAs). This is compatible with a conformational (discontinuous) nature of the epitopes involved in many false positive HIV-1 p24 antibody reactions. Four sera reacted with an N-terminal, one with an internal, and two with a C-terminal fragment. Each of the seven sera thus only reacted with one of the long p24 peptides. The specificity and singularity of the reaction was further demonstrated by competition and/or absorption experiments with synthetic peptides. In contrast, 18 of 20 confirmed HIV-1+ sera with p24 reactivity in EIB reacted with at least one and often several of the longer peptides, most frequently the C-terminal one. Thus, the distribution of peptide reactivity of true HIV-1 antibody-positive sera was different from that of the falsely reactive sera. According to two of several explanations, these antibodies may have arisen because of (1) molecular mimicry by chance or by functional selection, (2) immunization by activation, noninfectious exposure, or infection involving non-HIV endogenous or exogenous retroviral antigens. The latter gains some support from our finding of antibody reactions with capsid proteins of the simian viruses, simian sarcoma-associated virus (SSAV), and Mason-Pfizer monkey retrovirus in some of the p24 +/- p55 reactive sera.

A quantitative enzyme-linked immunosorbent assay for bovine herpesvirus type 1 (BHV-1) antibody

A quantitative enzyme-linked immunosorbent assay (ELISA) was developed to detect and measure antibody to bovine herpesvirus type 1 (BHV-1) in cattle sera. The optical density produced from a single dilution of test serum was compared with a standard curve and the results were read and printed out from a computer interfaced to a multichannel ELISA reader. The printed results were expressed in ELISA units. The ELISA results obtained on 370 cattle sera were compared with those of the serum neutralisation test (SNT). An agreement of 90.5% was obtained when reciprocal SNT titres equal to or greater than 4 and IgG ELISA units equal to or greater than 50 were taken as indicative of a specific reaction. Of the 370 sera, 35 gave discrepant results of which 21 were SNT positive/IgG ELISA negative and 14 were SNT negative/IgG ELISA positive. When the SNT positive sera negative in the IgG ELISA were tested in an IgM ELISA, 19 were found to be positive. Thus, when the IgG and IgM ELISA results were combined the overall agreement between the ELISA and SNT increased to 95.7%. The IgG ELISA had a sensitivity of 82.4% and specificity of 94.4% relative to the SNT, whereas the combined IgG and IgM ELISA results gave a sensitivity and specificity of 98.3% and 94.4% respectively. There was a good positive correlation between the two tests (r = 0.86).

Serological responses to papillomavirus group-specific antigens in women with neoplasia of the cervix uteri

Certain types of human papillomaviruses have been linked to the development of carcinoma of the cervix uteri. We have analyzed 114 serum specimens from women with cervical intraepithelial neoplasia (CIN) or carcinoma of the cervix uteri for the presence of serum antibodies against purified, disrupted bovine papillomavirus (BPV). The titers of immunoglobulin A (IgA) antibodies against BPV were slightly elevated (P less than 0.025) in the sera from CIN or cervical carcinoma patients compared with the titers of 139 serum specimens from sex- and age-matched healthy controls. In contrast, both the IgG and IgM serum antibody titers against BPV were significantly decreased for CIN and cervical carcinoma patients compared with those of healthy controls (P less than 0.001 and P less than 0.005, respectively). These results suggest that the difference between IgA and IgG or IgM antibodies to papillomavirus group-specific antigens may represent interesting serological parameters that could possibly be used in the epidemiologic study of women at risk for CIN.

Detection of antibodies to Helicobacter pylori cell surface antigens

Serum IgG antibodies of Helicobacter pylori were detected in single-dilution ELISA using glycine extracted material. Among 148 endoscopy patients 59% displayed antibodies; as expected, a higher occurrence (90%) was found in patients with positive gastric culture for H. pylori than in culture negative patients (37%). Among 68 blood donors the frequency of H. pylori antibodies was 28%. In 73 children less than 15 years of age examined for unrelated disorders the occurrence was 4%. By immunoblotting using the same extract, 3 prominent bands, 29K, 54K and 60K and several weak bands were identified. These were formed by 57%, 92%, and 65%, respectively, of the ELISA positive patient sera. Comparing culture positive and negative patients, the 3 bands occurred more often among the culture positive subjects though between 18 and 61% of the sera from culture negative patients gave either of the bands. When comparing the glycine extracts of 4 different H. pylori strains with separate haemagglutinating patterns no differences in the position of the major bands emerged. By absorption experiments no immunological cross-reactivity with components of Escherichia coli, Klebsiella pneumoniae, Campylobacter jejuni or C. fetus was found. Thus, the glycine extract seemed specific for the detection of antibodies to H. pylori.

Technical improvements of a commercial ELISA to detect antibodies against bovine herpesvirus 1

Prevention and control of the spread of IBR/IPV virus in cattle presumes exact diagnosis even with large sample collections. The requirements are fulfilled firstly by the application of the most sensitive testing methods for virus specific antibodies, such as the enzyme-linked immunosorbent assay (ELISA), and secondly by the introduction of bovine milk as a specimen for sampling. Data are presented demonstrating the application of a commercial ELISA system for evaluation of large sample collections and its optimization for this purpose.

Serum antibodies against respiratory tract viruses: a prospective three-year follow-up from birth

Acute otitis media (AOM) has been epidemiologically related to viral respiratory tract infections, and viral antigens have also been detected in middle ear secretion in some AOM episodes. Successive serum samples from children followed prospectively for three years from birth were analysed for IgG antibodies against respiratory syncytial virus (RSV), adenoviruses and influenza A virus. Values from serum antibody activity gradually decreased during the first six months of life, followed by a gradual increase. Various relationships were found to obtain between age and the increases of antibody activity against the different viruses. Thus, three quarters of those tested had manifested increased antibody activity against RSV by 18 months of age, and against adenoviruses by 30 months of age. No increase of antibody activity against influenza A was noted before 12 months of age, and then only seen in two thirds of those tested during the entire three-year observation period. With regard to age, however, the proportion of children with increased antibody activity to RSV, adenoviruses or influenza A virus did not differ between otitis-prone and non-otitis-prone children. Thus, as compared to non-otitis-prone children, development of the ability to produce antibodies against these viruses was not found to be delayed in otitis-prone children.

Detection of IgA antibodies against human papillomavirus in cervical secretions from patients with cervical intraepithelial neoplasia

Although human papillomavirus (HPV) is involved in the etiology of cervical carcinoma, there are no cervical carcinoma-specific HPV serologic tests available. We investigated the presence of broadly cross-reactive IgA antibodies to papillomavirus (PV) in cervico-vaginal secretions from patients with condylomata and cervical intraepithelial neoplasia (CIN). Purified bovine PV (BPV) virions were used as antigen in an enzyme-linked immunosorbent assay (ELISA). Forty-two women whose ages ranged from 20 to 50 participated in the study. Eight of 9 patients with CIN had IgA antibodies against PV in their cervical secretions. Three of 9 patients with koilocytosis and condylomas but no CIN had IgA antibodies to PV. Six of 24 women with normal Pap-smear and colposcopy also had IgA antibodies against PV in their cervical secretions. The proportion of IgA-positive cervical secretions was significantly higher in the CIN group than in the normal group (p less than 0.005). Our data suggest that IgA antibodies to PV may be a useful marker for CIN.

Presence of antibodies to a putatively immunosuppressive part of human immunodeficiency virus (HIV) envelope glycoprotein gp41 is strongly associated with health among HIV-positive subjects

The IgG response to gp41 (envelope glycoprotein of Mr 41,000) of the human immunodeficiency virus (HIV) was studied with eight synthetic peptides derived from three different regions of the protein. We tested sera from 17 HIV-seronegative and 68 HIV-seropositive subjects in an enzyme immunoassay. No HIV antibody-negative serum reacted with any of the peptides. The peptide HIV-env 583-599 has a sequence similarity with immunosuppressive peptides derived from the transmembrane proteins of other retroviruses. Antibodies to this 17-mer (HIV-env 583-599; hereafter also referred to as pHIVIS, putative HIV immunosuppressive sequence) were detected in 27 of the 35 sera from healthy HIV-positive persons but only in 1 of the 33 sera from patients with HIV-related disease. Another 17-mer, displaced four amino acids N-terminally from pHIVIS, reacted with fewer of the sera from healthy seropositive subjects than pHIVIS but with no serum from ill seropositive patients. HIV-env 586-603, which shares two-thirds of its sequence with pHIVIS, reacted with the sera from nearly all subjects, regardless of clinical status. The remaining five peptides did not discriminate between healthy and ill seropositive subjects either but gave lower reactivity rates. HIV-positive sera thus exhibited distinct patterns of reactivity with subsequences of gp41. We have mapped two overlapping epitopes within a narrow part of gp41; antibodies to the most N-terminally located of the two--i.e., the pHIVIS-reactive antibodies--might counteract a possible immunosuppressive effect of gp41.

The efficiency of various laboratory methods for the diagnosis of adenovirus conjunctivitis

Virological and serological data from 242 patients with conjunctivitis or keratoconjunctivitis, infected with adenovirus type 8, and of 109 patients infected with other adenovirus types were compared by means of an electronic data processing system. About 55% of the patients in both groups showed a diagnostic antibody rise in genus-specific (antihexon) complement-fixation. This rate is significantly lower than that obtained with genus-specific ELISA IgG or IgA, or with neutralization tests against the homologous virus, or with hemagglutination-inhibition in case of adenovirus 8 infection. All these tests showed titer rises in 72 to 85% of the patients; differences were not significant. Virus isolation from conjunctival swabs, taken up to 9 days after onset of disease, was successful in 80 to 90%, thereafter in 30%. The time-course of the various antibody titers showed that genus-specific (antihexon) antibodies mostly rise 9 to 12 days after onset, whereas type-specific neutralizing or hemagglutination-inhibiting antibodies rise 10 to 14 days after onset.

Anti-herpes simplex type 1 activity in IgG subclasses produced systemically and intrathecally in patients with herpes encephalitis

The role of the humoral immune response in herpes simplex encephalitis (HSE) is largely unknown. The finding that herpes simplex virus type 1 (HSV 1) induced IgG Fc receptor binds to all IgG subclasses except IgG 3 prompted an investigation of anti-HSV activity in IgG subclasses from serum and cerebrospinal fluid (CSF) in ten patients with proven or highly probable HSE by means of a monoclonal antibody IgG subclass-specific solid-phase radioimmunoassay (SPRIA). In contrast to serum, CSF contained no or low anti-HSV IgG titres during the first 2 weeks of disease in five of seven patients tested. The IgG titres rose thereafter for at least 4 weeks after the start of illness and remained high in both serum and CSF up to 393 days. The anti-HSV IgG subclass distribution in serum was IgG 1 (ten of ten), IgG 2 (two of ten), IgG 3 (six of ten), and IgG 4 (six of ten). Two patients had a simultaneous anti-HSV IgG 3 and IgG 4 response. With the exception of one patient lacking anti-HSV IgG 4 and two patients lacking anti-HSV IgG 2, the subclass distribution in CSF was the same as in serum. The anti-HSV subclass distribution in sera from ten seropositive patients without evidence of recent herpes infection did not differ from that of the HSE patients, except that five of ten patients had simultaneous anti-HSV IgG 3 and IgG 4 responses. Thus we could not correlate the anti-HSV subclass response in patients with HSE with the subclass preference of the HSV-induced Fc receptor.

Antibodies to human adult T cell leukaemia virus type I associated antigens in Swedish leukaemia patients and blood donors

Antibodies to antigens associated with human T cell leukaemia virus type I (HTLV I) in Swedish adult leukaemia patients and blood donors were sought with a sensitive screening test using membrane antigen prepared from virus producing cells (MA-ELISA). Four persons (one ALL, one AML and two healthy blood donors) out of 483 persons tested reacted in the test. However, they were negative in the more specific anti-p19 and anti-whole virion ELISA tests. The prevalence of sera with definite anti-HTLV I activity seems to be very low in Sweden. The finding of four MA-ELISA positive persons needs further investigation.

HTLV in Sweden: antibodies to HTLV I antigens in experimental monkeys and their caretakers

252 monkeys kept at 4 different Swedish universities and laboratories for experimentation were screened for antibodies to HTLV I associated antigens by means of a sensitive membrane antigen enzyme immunoassay (MA-ELISA). 17/185 Macaca fascicularis, 1/56 M. mulatta, 0/1 Cercopithecus aetiops and 0/10 Saimirii squiureus had antibodies. All of 11 MA-ELISA positive animals which were subjected to further testing were also positive in a competition assay for anti-HTLV p19 antibodies and in an anti-whole virion enzyme immunoassay. One colony of 32 M. fascicularis monkeys from the Philippines contained 7 antibody-positive animals. Except for one M. fascicularis which suffered from a chronic dermal lesion, major disease was not observed in any of the antibody-positive animals. None of 28 animal caretakers or experimenters, of which several had been repeatedly exposed to blood from antibody-positive animals, had antibodies measurable by the MA-ELISA. The contagiosity for humans of the majority of the antibody-positive monkeys thus appears to be relatively low. We conclude that the presence in Sweden of HTLV I antibody-positive animals probably does not constitute a great health risk. However, we consider it appropriate that antibody-positive animals should be handled with special care.

Enzyme immunoassay, complement fixation and hemagglutination inhibition tests in the diagnosis of influenza A and B virus infections. Purified hemagglutinin in subtype-specific diagnosis

The efficacy of enzyme immunoassay (EIA) in detecting diagnostic antibody rises to influenza A and B viruses was compared with complement fixation (CF) and hemagglutination inhibition (HI) tests in 455 patients with an acute respiratory infection. EIA and HI detected significantly more diagnostic antibody rises against influenza A than the CF method (96 and 87 vs. 47, respectively). In the case of influenza B significantly more diagnostic influenza B antibody rises were observed by EIA than by CF or HI (59 vs. 37 and 40, respectively). In most of the cases antibody rises in EIA were found in both IgG and IgA isotypes whereas increases in IgM antibodies were seen less frequently. Purified hemagglutinins (HA) were prepared from influenza A HI- and H3-subtypes and from influenza B viruses and used as antigens in EIA and the results were compared with those of HI. Infections caused by influenza A HI-subtype showed good homologous antibody responses in EIA but heterologous antibody responses to H3-subtype and influenza B HAs were frequently observed. Heterologous responses were clearly less frequent in patients with infections caused by the H3-subtype. Influenza B infections occasionally raised HA antibodies against influenza A H1-subtype but not to the H3-subtype. Interestingly, HI detected these heterologous responses at least as frequently as EIA. When whole viruses were used as antigens in EIA, subtype specificity was not observed and cross-reactions between influenza A and B virus antibodies were found. These observations suggest that, although EIA can show greater diagnostic efficacy over HI and CF methods, HI is still the serological method of choice in determining the causative subtype of influenza A virus infection.

A single dilution enzyme-linked immunosorbent assay for the quantitative detection of antibodies to bovine herpesvirus type 1

Three serological assays were compared for detection of antibodies to bovine herpes-virus type 1. These were virus neutralization (VN), enhanced complement fixation (CF) and enzyme-linked immunosorbent assay (ELISA). The ELISA was developed using an infected cell lysate antigen and purified virus and was optimized in relation to antigen and antisera dilutions. The CF assay was enhanced by the addition of bovine complement. These 3 assays were compared for detection of: specific virus antibody titers; sero-conversions; early antibody response in experimentally-infected cattle. Both ELISA end-point titers and single dilution values were found to be more sensitive than the CF or VN assays for specific antibody level quantitation. With a single dilution ELISA test procedure a correlation was obtained between ELISA values and VN titers. Using the single dilution ELISA test the assay also detected antibodies in experimentally-infected cattle before either the VN or CF assays, and agreed with the VN test in 35/38 seroconversions found by 4-fold or more VN changes between acute and convalescent paired sera from naturally-infected animals. The single dilution ELISA was a rapid and sensitive test for routine antibody detection in bovine sera.

Immunoglobulin G antibodies binding to a synthetic peptide deduced from the nucleotide sequence of the env gene of HTLV I in patients with leukemia and rheumatoid arthritis, HLA sensitized persons and blood donors

A synthetic pentadecapeptide preparation, env 406-420, with an amino acid sequence deduced from the envelope glycoprotein gene of human T cell leukemia virus type I (HTLV I), was used as the antigen in an enzyme immunoassay for immunoglobulin G antibodies, exploring its usefulness for seroepidemiological purposes. The frequency of reactivity in the test groups, presented in decreasing order was: patients with rheumatoid arthritis; multitransfused nonleukemic patients; Japanese cases of adult T cell leukemia (ATL); HLA sensitized persons; Swedish cases of adult acute leukemia; and Swedish blood donors. Three American cases of ATL and 12 HTLV I seropositive monkeys did not react. In RF positive sera from patients with rheumatoid arthritis, no quantitative correlation between RF activity and anti-env 406-420 activity was seen. Anti-env 406-420 positive sera did not react or reacted only weakly with four control peptide preparations with different amino acid sequences. The experience with oligopeptide serology still is limited. Our results illustrate that unexpected cross-reactions which are hard to interpret can occur. Although absorption experiments indicated an HTLV I specific component of the reactivity, antibodies against epitopes of allo- and auto-immune specificity may also have participated.

Detection of immunoglobulin M and G antibodies against cytomegalovirus early and late antigens by enzyme-linked immunosorbent assay

A sensitive and reproducible enzyme-linked immunosorbent assay (ELISA) is described for the detection of immunoglobulin M and antibodies with specifity for human cytomegalovirus (CMV) early (CMV-EA) and late (CMV-LA) antigens. The emphasis is on the production of high-quality CMV antigens, CMV-EA and CMV-LA separately, and conditions for their application in the ELISA. The induction of CMV-EA and -LA in infected cell extracts was studied in detail by using human sera with defined antibody specificity for CMV-EA and CMV-LA. This resulted in the development of a simple whole cell extraction procedure that provided a high yield of CMV antigens with reproducible antigen quality. The antigens were specific for the detection of anti-CMV antibodies. The influence of autoantibodies on the determination of CMV-specific antibodies was investigated. Parallel analysis of 322 human sera by indirect immunofluorescence and ELISA showed a high correlation between both assays (r = 0.9674 for CMV-EA and 0.9362 for CMV-LA). Antibody titers determined by ELISA were equal to (for CMV-EA) or slightly higher (for CMV-LA) that those determined by immunofluorescence but significantly higher (20- to 5,120-fold) than those determined by complement fixation. From 191 sera positive by ELISA (titer greater than or equal to 40) 4 (2.1%) were negative by immunofluorescence (titer less than 40), and from 61 ELISA-positive sera 12 (19.6%) were negative (titer less than 8) when tested by complement fixation. Consequently, ELISA for CMV may prove to be more reliable for the selection of CMV-seronegative blood donors than these other methods. The use of high-quality antigens allows more economic handling of large-scale serum determinations. Possibilities for further automation are discussed.

Human immunoglobulin class and subclass specificity of Fc receptors induced by herpes simplex virus type 1

Herpes simplex virus is known to induce an immunoglobulin-binding cell surface receptor in infected cells that utilizes a nonimmune mechanism. In the present paper, we report the immunoglobulin class and subclass specificity of this receptor. Of the human immunoglobulins G(IgG), IgA, IgM, and IgD, as well as the structurally related beta2 microglobulin, only IgG and its Fc portion exhibited an increased binding to herpes simplex virus-infected cells versus uninfected control cells. The IgG subclass specificity of the Fc receptor was studied in 37 radioiodinated IgG myeloma proteins representing all four subclasses. We found that IgG3 myeloma proteins did not bind to herpes simplex virus-infected cells to a greater extent than to uninfected cells. On the contrary, proteins belonging to the other subclasses exhibited an increased binding to herpes simplex virus-infected cells of the following relative magnitude: IgG4 greater than IgG1 greater than or equal to IgG2. This increment of binding could be abolished by addition of a large excess of human IgG Fc fragment. Evidence for the existence of a variable herpes simplex virus-specific binding ability between myeloma proteins belonging to the same IgG subclass was also obtained. Furthermore, we tested two other herpes simplex virus type 1 strains with a limited number of myeloma proteins with very similar results as with the herpes simplex virus type 1 F strain. Several sources of experimental artefacts were controlled, including the state of aggregation of the test proteins, the functional integrity of the Fc portion before and after radioiodination, and the subclass assignments. The implications for the biological role of the Fc receptor of herpes simplex virus are discussed.

Enzyme-linked immunosorbent assay for evaluation of immunity to measles virus

An enzyme-linked immunosorbent assay for the determination of immunity to measles virus was developed and standardized; it was compared to the hemagglutination inhibition and plaque reduction neutralization methods for sensitivity and specificity. The conditions of the enzyme-linked immunosorbent assay were adjusted such that groups of susceptible and immune individuals were clearly separable on the basis of the reactivity of a single (1:100) dilution of their sera to viral and control antigens. The range of values corresponding to susceptibility and immunity was defined by using the distribution of values observed from testing sera obtained from susceptible and immune control groups. The enzyme-linked immunosorbent assay was then applied in a study of measles vaccinees and found to be more sensitive than the hemagglutination inhibition method and equal in sensitivity to the plaque reduction neutralization method. The three methods were equal in specificity. Thus, the measles virus enzyme-linked immunosorbent assay is a rapid, reproducible, sensitive, and specific method for screening for the presence of measles antibody.