Monoclonal antibody-based capture enzyme immunoassays for specific serum immunoglobulin G (IgG), IgA, and IgM antibodies to respiratory syncytial virus

Monoclonal antibodies (MAbs) to the fusion protein (F), attachment protein (G), and nucleoprotein (N) of respiratory syncytial (RS) virus were evaluated for use as detector antibodies in immunoglobulin G (IgG), IgA, and IgM capture enzyme immunoassays. MAb assays were tested against assays using polyclonal antibodies (PAbs) with serum specimens from patients with and without evidence of recent RS virus infection. Assays developed with N MAbs were comparable to or better than PAb assays for detecting specific IgG and IgM antibodies but were somewhat less sensitive for IgA. F MAb assays were less sensitive for IgG and IgM antibodies but identified specific IgA in some specimens negative by N MAb assay. G MAb assays were insensitive for IgG and IgM antibodies but did detect about 50% of the IgA antibodies identified by the PAb assay. The basis for the low sensitivity of the G MAb assays is unclear, since many of these specimens were positive for IgG antibodies to G by Western immunoblot. The sensitivity of MAb assays varied with patient age: N MAb assays detected specific antibody responses to RS virus in all immunoglobulin classes in both adults and infants less than 1 year of age, F MAb assays detected specific IgG responses in adults and IgA responses in both adults and infants, and G MAb assays only detected IgA responses in adults. A mixture of N and F MAbs was complementary overall, identifying 54 of 55 (IgG), 51 of 52 (IgA), and 16 of 17 (IgM) serum specimens positive by PAb assay. These MAb assays were also specific with specimens tested from persons without a history of recent RS virus infection. The availability of these MAb-based assays offers other laboratories the opportunity to have long-term, standardized reagents and tests for serological diagnosis of RS virus infection.     

Reverse ELISA for IgG and IgM antibodies to detect Lassa virus infections in Africa.

BACKGROUND: Anti-Lassa antibodies are detected by indirect immunofluorescence assay (IFA) or by enzyme-immunoassay (ELISA). Both methods have problems to detect low amounts of specific antibodies. OBJECTIVES: We report here highly sensitive and specific reverse ELISAs to detect Lassa virus IgG and IgM antibodies. Due to the reverse techniques, serum samples could be applied at dilutions of 1:10 without increasing non-specific background reactions. STUDY DESIGN: For IgM antibody detection microtiter plates were coated with anti-IgM antibodies and for IgG antibody detection with rheumatoid factor (RF) (Sachers M, Emmerich P, Mohr H, Schmitz H. Simple detection of antibodies to different viruses using rheumatoid factor and enzyme-labelled antigen (ELA). J Virol Methods 1985;10:99-110). In both assays a tissue culture antigen was used in combination with a labeled anti-Lassa monoclonal antibody (Hufert FT, Ludke W, Schmitz H. Epitope mapping of the Lassa virus nucleoprotein using monoclonal anti-nucleocapsid antibodies. Arch Virol 1989;106(3-4):201-12). RESULTS: The reverse ELISA turned out to detect virus-specific IgG and IgM antibody in all 20 samples of West African patients collected 2-8 weeks after onset of Lassa fever. Moreover, both IFA and reverse ELISA found IgG antibodies in 53 out of 643 samples of healthy West Africans (sensitivity of 100%). Six of the 643 samples were positive by reverse IgG ELISA only. Thus, the specificity compared to IIF was 99.0%, but it may be even higher, because compared to IFA the IgG ELISA was clearly more sensitive in detecting low antibody titers. CONCLUSIONS: In Ghana 3% seropositives were found by IFA, but 4% by the reverse ELISA. The reverse ELISAs can be performed with high sensitivity and specificity under field conditions in Africa.     

Longitudinal profile of immunoglobulin G (IgG), IgM, and IgA antibodies against the severe acute respiratory syndrome (SARS) coronavirus nucleocapsid protein in patients with pneumonia due to the SARS coronavirus

By using a recombinant severe acute respiratory syndrome coronavirus (SARS-CoV) nucleocapsid protein-based enzyme-linked immunosorbent assay (ELISA) and serum specimens serially collected (from day 0 to day 240 after symptom onset) from patients with pneumonia due to SARS-CoV, we analyzed the longitudinal profiles of immunoglobulin G (IgG), IgM, and IgA antibodies against the SARS-CoV nucleocapsid protein in patients with pneumonia due to SARS-CoV. For IgG, the median optical density at 450 nm (OD450) turned positive at day 17 and a biphasic response was observed. At day 240, all patients were still positive for anti-nucleocapsid protein IgG antibody. For IgM, the median OD450 turned positive at day 20.5, peaked at about day 80, and fell to below the baseline level at about day 180. At day 240, 36% of the patients were still positive for anti-nucleocapsid protein IgM antibody. For IgA, the median OD450 turned positive at day 17, peaked at about day 50, and fell to below the baseline level at about day 180. At day 240, 36% of the patients were still positive for anti-nucleocapsid protein IgA antibody. The time of seroconversion detected by the recombinant SARS-CoV nucleocapsid protein-based ELISA and that detected by indirect immunofluorescence assay were similar. The median times of seroconversion for IgG, IgM, and IgA detected by the indirect immunofluorescence assay were 17 days (17 days by ELISA), 16.5 days (20.5 days by ELISA), and 17.5 days (17 days by ELISA), respectively, after disease onset. One, four, and one of the six patients who died did not produce any IgG, IgM, and IgA antibodies against the nucleocapsid protein of SARS-CoV, respectively, although these antibodies were detected in all six patients by the indirect immunofluorescence assay. Further studies should be performed to see whether SARS-CoV nucleocapsid protein antibody positivity has any prognostic significance.     

用重组汉坦病毒NP、GP检测急性期HFRS患者血清中特异性IgG、IgM、IgA抗体

目的 探讨肾综合征出血热(HFRS)患者急性期IgA、IgG、IgM抗体的变化规律。方法 使用套式RT-PCR检测此次病毒感染情况。用杆状病毒表达的汉坦病毒重组核蛋白(rNP)和糖蛋白(rGP)为抗原，使用ELISA方法检测了14例急性期肾综合征出血热患者的6l份系列血清中的IgA、IgG、IgM抗体。结果 14例肾综合征出血热患者中，ll例患者的血清用RT-PCR检出家鼠型汉坦病毒核酸。几乎所有肾综合征出血热患者早期即有IgA、IgM、IgG抗体的迅速升高，抗rNP抗体滴度明显高于rGP。3种抗rNP抗体中早期IgG上升趋势最为显著，IgM与IgA次之，IgM与IgA上升趋势相近，但IgA的滴度明显高于IgM。抗rGP抗体中XgA变化最显著，IgG次之。IgM发病2周内总的变化趋势不明显，但是发病l周内滴度上升趋势明显，而发病第2周内则呈下降趋势。其中l例RT-PCR阳性的患者，早期IgM未测出，IgA的滴度却较高。l例重度患者，抗糖蛋白IgG、IgM和IgA抗体滴度均低于其他患者，且整个急性期一直维持较低水平。结论 肾综合征出血热急性期IgA、IgG、lgM变化具有明显的规律，抗糖蛋白和核蛋白抗体病患规律不同，检测IgM的同时检测IgA，可以提高诊断的准确性。     

Neutralizing serum IgM antibodies in infections withHerpes simplex virus hominis

Forty-two patients with herpes simplex virus infections were tested for neutralizing serum IgM antibodies. A technique in which serum antibody fluorescein staining was combined with sucrose gradient centrifugation facilitated the isolation of the serum IgM fraction for the use in neutralization tests. In nearly all cases with primary infection, especially those presenting heavy clinical signs (encephalitis/meningitis) the IgM tests were positive. In one case we could detect the IgM antibodies for 11 weeks after the onset of the illness, in another case in cerebrospinal fluid samples for 6 weeks. In localized herpes infections, which were mostly due to reactivations, serum IgM antibodies could only rarely be demonstrated. Among the serologic tests used in this study (NT, CFT, IFT, ACIFT), only the CFT beside the NT (with certain reservations) can be applied for subtyping HSV serum antibodies.The work was supported by the Deutsche Forschungsgemeinschaft, SFB 31.     

Enzyme-linked immunosorbent assay for mumps IgM antibody: comparison of IgM capture and indirect IgM assay

We have established two enzyme-linked immunosorbent assays (ELISAs) for detection of mumps IgM antibody, i.e., indirect IgM ELISA and IgM capture ELISA, for serodiagnosis of recent mumps infection. In the latter method, peroxidase-conjugated monoclonal antibody to mumps virus was employed. Both methods detected mumps antibody of IgM class only in serum fractions separated by centrifugation through a sucrose density gradient. Optical density values given by both ELISAs were correlated for most sera examined. Indirect IgM ELISA, however, gave a false positive reaction for sera containing both rheumatoid factor and mumps IgG antibody, while giving a false negative reaction for sera containing high titers of mumps IgG antibody. This technique was, therefore, less reliable than IgM capture ELISA. IgM antibody detectable by IgM capture ELISA was present in all patients with mumps by the fifth day of illness and persisted for up to 3 mth in most and up to 5 mth in same cases.     

Evaluation of immunoglobulin M (IgM) and IgG enzyme immunoassays in serologic diagnosis of West Nile Virus infection

A unique urban encephalitis epidemic in Romania signaled the emergence of neurological infection due to West Nile (WN) virus as a novel public health threat in Eastern Europe and provided an opportunity to evaluate patterns of immunoglobulin G (IgG) and IgM reactivity in IgM capture and IgG enzyme-linked immunosorbent assays (ELISAs). WN virus infection was diagnosed serologically in 236 of 290 patients from whom acute serum or cerebrospinal fluid (CSF) samples were available. In 37% of serum samples and in 25% of CSF samples collected in the first week of illness, anti-WN virus IgM antibody was detected in the absence of virus-specific IgG. The switch to an IgG antibody response occurred after 4 to 5 days of illness and earlier in CSF than in serum. A specific humoral immune response was detected in the CSF before the serum in some patients for whom paired CSF and serum samples from the same day were available. IgM antibody in convalescent serum samples persisted beyond 2 months after the onset of illness in more than 50% of patients. ELISA optical density values and antibody concentrations were well correlated for both IgM and IgG immunoassays. Anti-WN virus IgM antibody in acute-phase samples did not cross-react significantly with flaviviruses in other antigenic groups.     

Chronological evolution of IgM, IgA, IgG and neutralisation antibodies after infection with SARS-associated coronavirus

Abstract Serum levels of IgG, IgM and IgA against severe acute respiratory distress syndrome (SARS)-associated coronavirus (SARS-CoV) were detected serially with the use of immunofluorescent antibody assays in 30 patients with SARS. Seroconversion for IgG (mean 10 days) occurred simultaneously, or 1 day earlier, than that for IgM and IgA (mean 11 days for both). IgG could be detected as early as 4 days after the onset of illness. The earliest time at which these three antibodies reached peak levels was similar (mean 15 days). A high IgG level (1:800) could persist for > 3 months. The kinetics of neutralisation antibodies obtained with 100x the tissue culture infective dose (TCID50) of the SARS-CoV TW1 strain in five patients with SARS nearly paralleled those for IgG. There were no significant differences in the kinetics of the IgG, IgM and IgA responses between patients with or without underlying medical disease, steroid or intravenous immunoglobulin therapy, or mechanical ventilation.     

Simultaneous detection of immunoglobulin A (IgA) and IgM antibodies against hepatitis E virus (HEV) Is highly specific for diagnosis of acute HEV infection

Serum samples collected from 68 patients (age, mean +/- the standard deviation [SD], 56.3 +/- 12.8 years) at admission who were subsequently molecularly diagnosed as having hepatitis E and from 2,781 individuals who were assumed not to have been recently infected with hepatitis E virus (HEV; negative controls; 52.9 +/- 18.9 years), were tested for immunoglobulin M (IgM) and IgA classes of antibodies to HEV (anti-HEV) by in-house solid-phase enzyme immunoassay with recombinant open reading frame 2 protein expressed in the pupae of silkworm as the antigen probe. The 68 patients with hepatitis E had both anti-HEV IgM and anti-HEV IgA. Among the 2,781 controls, 16 (0.6%) had anti-HEV IgM alone and 4 (0.1%) had anti-HEV IgA alone: these IgA/IgM anti-HEV-positive individuals were not only negative for HEV RNA but lack IgG anti-HEV antibody as well (at least in most of the cases). Periodic serum samples obtained from 15 patients with hepatitis E were tested for HEV RNA, anti-HEV IgM, and anti-HEV IgA. Although HEV RNA was detectable in the serum until 7 to 40 (21.4 +/- 9.7) days after disease onset, both IgM and IgA anti-HEV antibodies were detectable until 37, 55, or 62 days after disease onset in three patients and up through the end of the observation period (50 to 144 days) in 12 patients. These results indicate that detection of anti-HEV IgA alone or along with anti-HEV IgM is useful for serological diagnosis of hepatitis E with increased specificity and longer duration of positivity than that by RNA detection.     

Diagnosis of enterovirus 70 infection by demonstration of IgM antibodies

Since outbreaks of severe acute hemorrhagic conjunctivitis occur worldwide [Hierholzer and Hatch, 1985] and the majority of the epidemics are caused by enterovirus 70 (EV-70), we developed an EV-70 IgM ELISA to simplify the diagnosis of these outbreaks. The test is based on the capture antibody technique and the use of monoclonal antibodies to EV-70. We detected EV-70 IgM antibodies in 55% of 76 convalescent-phase sera from an outbreak of acute hemorrhagic conjunctivitis in a Brazilian community. Among the 71 acute- and convalescent-phase serum pairs from this outbreak, 49 (69%) demonstrated a 4-fold or greater rise in neutralizing antibody-titer. The titer of IgM antibody began to drop by the fifth week after onset of illness. EV-70 IgM antibodies were not detected in 53 serum pairs with a 4-fold or greater rise in antibodies to other picornaviruses. The EV-70 ELISA proved to simple and relatively rapid to perform, appeared to be specific, and should be sensitive enough to diagnose outbreaks of EV-70 when multiple serum specimens can be tested.     

Monoclonal antibodies used to isolate IgM from chicken bile and avian sera and to detect specific IgM in chicken sera

Four hybridoma cell lines (designated M1, M10, M11, M31) were established which secrete antibody specific for chicken IgM. The specificity for the IgM heavy chain was shown by using ELISAs to screen for antibodies to IgM, IgA and IgG. Radioimmunoprecipitation tests confirmed that the four monoclonal antibodies reacted with IgM and also showed that they combined with Protein A. An immunoadsorbent was made using one (M1) of the monoclonal antibodies. IgM was purified in a single step by affinity chromatography from chicken bile and chicken, turkey and duck serum. This is the first unequivocal demonstration of chicken IgM in bile. The Ml monoclonal antibody was used in an ELISA to detect the specific chicken IgM response to the inoculation of bovine serum albumin. This anti-IgM reagent may also be used to detect the IgM response to other antigens.     

An enzyme-linked immunosorbent assay (ELISA) for IgG and IgA antibodies to respiratory syncytial virus in low dilutions of secretions of human serum and secretions

An enzyme-linked immunosorbent assay (ELISA) has been developed for titration of IgG and IgA antibodies to respiratory syncytial (RS) virus in low dilutions of human serum, colostrum, and nasopharyngeal secretions. Previously the sensitivity of RS virus ELISA on such specimens has been limited by nonspecific absorption of antibody, particularly IgA, to crude antigen preparations. For IgG antibody estimation in infant sera, this unwanted binding was reduced to workable levels by increasing the serum, salt, and detergent concentration of the diluent. Residual nonspecific binding of IgA in colostra appeared mainly due to antigen lipids or to lipoproteins. This was markedly reduced by partitioning Triton X-100-treated infected cell lysate antigens in Arklone. Using the modified ELISA technique for anti-RS virus IgA, good correlations were found with unfixed cell membrane immunofluorescence (MIF) for colostra (r = 0.81, P less than 0.001) and nasal secretions from adult volunteers. In several samples nonspecific absorption of antibody precluded MIF assay, but did not affect the ELISA. Although there was an overall correlation between ELISA for anti-RS IgG antibody in sera, the complement fixation test (r = 0.75, P less than 0.001), and MIF test (r = 0.82, P less than 0.001), the sensitivity of ELISA for antibody responses in convalescent sera of infants from 3 months to 2 years was poor. Conversely, the sensitivity of ELISA for antibody in the sera of older children and for transplacentally acquired antibody in very young infants was higher than that for the other two tests. ELISA was thus less reliable than either CF or MIF for detecting antibody rises in paired infant sera, particularly where maternally acquired antibody remained in the acute serum. The reasons for this apparent disparity are discussed.     

Detection by ELISA of IgG-subclass-specific antibodies in primary respiratory syncytial (RS) virus infections

The IgG-subclass specific antibody response was investigated in primary RS-virus infections in infants and small children by using an ELISA with monoclonal antibodies against the four human IgG subclasses. When 78 serum samples obtained from 21 patients during the first 3-4 mo following the onset of illness were studied, only IgG-1 and IgG-3 antibodies could be detected. Both of these subclass specific antibodies appeared during the second week following the beginning of illness. Approximately 4 wk after the onset of illness, IgG-1 antibodies reached maximum levels, which persisted during the following months. Approximately 3 wk after the onset of illness, IgG-3 antibodies reached maximum levels, which decreased during the following months. Both IgG-1 and IgG-3 antibodies showed neutralizing capacity.     

Local production of mumps IgG and IgM antibodies in the cerebrospinal fluid of meningitis patients

Immunoglobulin G (IgG) and M (IgM) antibodies against mumps virus were measured by an enzyme-linked immunosorbent assay (ELISA) in the serum and cerebrospinal fluid (CSF) specimens of patients with mumps meningitis. The CSF IgG antibodies correlated well with the respective antibody titers in serum. On the contrary, in only about half of the patients a moderate correlation was found between the CSF and serum IgM antibody titers, while the other patients did not have detectable mumps IgM antibodies in CSF irrespective of intermediate to high titers in serum. Two different immunologic mechanisms may be involved in these two groups which, however, did not show any clinical differences. The lack of IgM antibodies in the CSF of many patients diminished the value of CSF in the laboratory diagnosis of mumps meningitis compared to use of serum specimens. Intrathecal synthesis of mumps IgG antibodies was demonstrated in 83% of the patients, and of IgM antibodies in at least 67% of those patients with detectable IgM antibodies in CSF. The ratio between mumps IgG and IgM antibodies was higher in CSF than in serum, suggesting that the synthesis of IgG antibodies in central nervous system was more efficient than that of IgM antibodies.     

Enzyme-linked immunosorbent assay for IgG and IgM antibodies against human parvovirus B19: use of monoclonal antibodies and viral antigen propagated in vitro

Enzyme-linked immunosorbent assay (ELISA) systems for serum IgG and IgM antibodies to human parvovirus B19 were established by utilizing anti-B19 monoclonal antibodies (mAbs) and human plasma B19 antigen. The specificities of IgG and IgM ELISA were confirmed by indirect immunofluorescence staining and Western blot immunoassay with panel sera. The series of serum specimens obtained from two B19-infected patients were examined with ELISA. The IgM antibody titers increased quickly after the onset of the symptoms and returned to a negative range after five months. The IgG antibody titers also increased just after the increasing of IgM titers and the elevated levels continued for more than a year. We also established the same ELISA systems by utilizing in vitro propagated B19 antigen and similar results were obtained.     

Class-specific antibody determination against Aspergillus fumigatus by means of the enzyme-linked immunosorbent assay. III. Comparative study: IgG, IgA, IgM ELISA titers, precipitating antibodies and IgE binding after fractionation of the antigen

IgG, IgA and IgM ELISA antibody titers against Aspergillus fumigatus were elevated in sera of patients with aspergilloma and allergic bronchopulmonary aspergillosis (ABPA), showing higher titers for the IgG antibodies compared with the IgA and IgM antibodies. No differences were found between titers of identical antibody classes in the two groups of sera. IgG and IgA ELISA titers were highly specific whereas IgM ELISA showed more unspecific binding of IgM antibodies. Antibodies, as measured by ELISA, studied after fractionation of the antigen into fractions of decreasing molecular weight, showed a preferential binding by the high molecular weight fractions. Precipitating antibodies studied in patient sera did not always correspond with the IgG ELISA titers. IgE antibody binding was observed in all fractions from Sephadex G-100 fractionated components; maximum binding was found with fractions of 28,000-60,000 daltons. The low molecular weight fractions (18,000-less than 5,000 daltons) showed less IgE binding but the quantity of this fraction was higher. The discrepancies noted between the IgG and IgA ELISA titers and the binding of IgM or IgE antibodies indicate that antigenic components may in part differ in the binding of antibody classes.     

Diagnosis of Colorado tick fever virus infection by enzyme immunoassays for immunoglobulin M and G antibodies.

An immunoglobulin M (IgM) capture enzyme immunoassay technique was adapted for the detection of antibody to Colorado tick fever virus in sera from 84 individuals for whom diagnosis had been confirmed by virus isolation or neutralization test. Titers were compared with those for IgG and neutralizing antibodies in these Colorado tick fever cases. IgM antibody titers were higher than neutralizing antibody titers, but neither appeared until 1 to 2 weeks after the onset of illness. Neutralizing antibodies were detected earlier than IgM antibodies, and both were detected with greater frequency than IgG antibodies. Late-convalescent-phase sera contained both neutralizing and IgG antibodies, but IgM was all but undetectable by 2 months after onset. Although the neutralization test may remain the serological test of choice, the enzyme immunoassay for IgM antibody offers a simple and more rapid method of serodiagnosis; the enzyme immunoassay is, however, less sensitive than the neutralization test. Furthermore, because there was a sharp decline in IgM antibody after 45 days, the presence of IgM antibody in a single serum sample provides a basis for the presumptive serodiagnosis of recent Colorado tick fever virus infection.     

Kinetics of specific IgA, IgD, IgE, IgG, and IgM antibody responses in rubella

Rubella-specific IgD and IgE antibodies were determined with a solid-phase enzyme immunoassay using enzyme-labeled heavy-chain specific anti-immuno-globulins, and the antibody responses in rubella infection were compared to IgM, IgA, and IgG antibodies. IgD and IgE antibodies increased rapidly after the onset of infection, remained at a high level for at least 2 months, and declined slightly by 6 months. In comparison, the IgM antibodies decreased more rapidly, whereas the IgG antibodies persisted longer at a steady level. By 6 months the mean levels of the different antibodies had declined from their maximal mean levels as follows: IgM, 52%; IgA, 42%; IgE, 35%; IgD, 29%; and IgG, 8%. Thus IgD and IgE antibodies, in spite of their known short half lives, persisted longer than IgM and IgA antibodies, which limits their diagnostic value. The IgA antibody responses were found too variable to substitute for IgM antibody determination in diagnosis of a recent rubella virus infection from a single serum specimen. Comparison of maternal and cord blood sera indicated that, in addition to IgG antibodies, rubella-specific IgD antibodies were found to cross the placenta.     

Longitudinal Profile of Immunoglobulin G (IgG), IgM, and IgA Antibodies against the Severe Acute Respiratory Syndrome (SARS) Coronavirus Nucleocapsid Protein in Patients with Pneumonia Due to the SARS Coronavirus

By using a recombinant severe acute respiratory syndrome coronavirus (SARS-CoV) nucleocapsid protein-based enzyme-linked immunosorbent assay (ELISA) and serum specimens serially collected (from day 0 to day 240 after symptom onset) from patients with pneumonia due to SARS-CoV, we analyzed the longitudinal profiles of immunoglobulin G (IgG), IgM, and IgA antibodies against the SARS-CoV nucleocapsid protein in patients with pneumonia due to SARS-CoV. For IgG, the median optical density at 450 nm (OD₄₅₀) turned positive at day 17 and a biphasic response was observed. At day 240, all patients were still positive for anti-nucleocapsid protein IgG antibody. For IgM, the median OD₄₅₀ turned positive at day 20.5, peaked at about day 80, and fell to below the baseline level at about day 180. At day 240, 36% of the patients were still positive for anti-nucleocapsid protein IgM antibody. For IgA, the median OD₄₅₀ turned positive at day 17, peaked at about day 50, and fell to below the baseline level at about day 180. At day 240, 36% of the patients were still positive for anti-nucleocapsid protein IgA antibody. The time of seroconversion detected by the recombinant SARS-CoV nucleocapsid protein-based ELISA and that detected by indirect immunofluorescence assay were similar. The median times of seroconversion for IgG, IgM, and IgA detected by the indirect immunofluorescence assay were 17 days (17 days by ELISA), 16.5 days (20.5 days by ELISA), and 17.5 days (17 days by ELISA), respectively, after disease onset. One, four, and one of the six patients who died did not produce any IgG, IgM, and IgA antibodies against the nucleocapsid protein of SARS-CoV, respectively, although these antibodies were detected in all six patients by the indirect immunofluorescence assay. Further studies should be performed to see whether SARS-CoV nucleocapsid protein antibody positivity has any prognostic significance.     

Diagnosis of dengue virus infection by detection of specific immunoglobulin M (IgM) and IgA antibodies in serum and saliva

To evaluate alternative approaches to the serological diagnosis of dengue virus (DEN) infection, the detection of DEN-specific immunoglobulin M (IgM) and IgA antibodies in serum and saliva specimens was assessed in 147 patients with symptoms of DEN infection seen at the Ministry of Health in Nicaragua. Seventy-two serum samples were determined to be positive for anti-DEN antibodies by IgM capture enzyme-linked immunosorbent assay, the routine diagnostic procedure. Serum and saliva specimens were obtained from 50 healthy adults as additional controls. IgM was detected in the saliva of 65 of the 72 serum IgM-positive cases, 6 of the 75 serum IgM-negative cases, and none of the control group, resulting in a sensitivity of 90.3% and a specificity of 92.0% and demonstrating that salivary IgM is a useful diagnostic marker for DEN infection. Detection of IgA in serum may be another feasible alternative for the diagnosis of DEN infection, with serum IgA found in 68 (94.4%) of the IgM-positive cases. In contrast, detection of IgA in saliva was not found to be a useful tool for DEN diagnosis in the present study. Further studies of the kinetics of antibody detection in another set of 151 paired acute- and convalescent-phase serum samples showed that DEN-specific IgA antibodies were detected in more acute-phase samples than were IgM antibodies. Thus, we conclude that DEN-specific IgA in serum is a potential diagnostic target. Furthermore, given that saliva is a readily obtainable, noninvasive specimen, detection of DEN-specific salivary IgM should be considered a useful, cheaper diagnostic modality with similar sensitivity and specificity to IgM detection in serum.