Detection of enterovirus specific IgG and IgM antibodies in humans by an indirect solid phase radioimmunoassay

Diagnosis of enteroviral meningitis with IgG-EIA using heat-treated virions and synthetic peptides as antigens

Two recently developed enzyme immunosorbent assays (EIA) for the detection of significant titre increases in enteroviral IgG-antibodies were evaluated as diagnostic tools in 127 etiologically well-characterized patients with aseptic meningitis. One assay was based on heat-treated virions (H-EIA) and one on synthetic peptides (P-EIA) as antigens. The sensitivities, with virus isolation as reference method, were 0.67 by H-EIA and 0.62 by P-EIA, which were higher than by a routinely used complement fixation test (CFT, 0.51) but somewhat lower than the sensitivities found by two previously presented IgM-assays, mu-capture EIA, and solid-phase reverse immunosorbent test (SPRIST). The specificities of the two IgG-EIA techniques and CFT were apparently high, whereas the two IgM-assays showed positive reactions in some non-enteroviral cases. A relatively rapid increase in enteroviral IgG-antibodies was apparent using H-EIA and P-EIA. The two IgG-EIA tests contributed with considerable additional etiological information since significant IgG-rises were obtained in 13 patients by H-EIA and in 19 by P-EIA, respectively, out of the 56 individuals in whom enterovirus isolation was negative and a non-enteroviral diagnosis was not found. Thus, detection of enteroviral IgG-antibodies by H-EIA and P-EIA seems to be a valuable alternative to CFT for the routine diagnosis of enteroviral meningitis. The IgM-assays, mu-capture EIA, and SPRIST, may allow a relatively rapid report of an enteroviral infection. However, since both the IgM-tests are hampered by incomplete specificities, a confirmation of positive results by an IgG-assay should be carried out.

Animal serum factor(s) causing adverse effects on RIAs of human enterovirus IgM

The effects of animal sera used at various concentrations in dilution buffers for radioimmunoassays (RIAs) of human enterovirus-IgM were studied. The origin of the sera had no impact on the titres, but adverse effects on virus-specificity tests were noted when sera from some species were used. In attempts to block the binding of 35S-labelled virus by adding unlabelled virus, sera from cow, horse and lamb and from swine and man could usually not be used; instead of a blocking effect, an increase in bound labelled virus was noted in most cases. When fetal or newborn calf serum or sera from chicken were used, this phenomenon did not occur. The factor(s) causing the enhancement of virus binding could not be identified, but it was evident that it was not present in all sera from the same species and it was very probable that immunoglobulins were not involved.

Enterovirus-specific IgM in the diagnosis of meningitis

Samples of serum from 557 patients with a clinical diagnosis of meningitis or encephalitis and referred to the Epsom Public Health Laboratory during a period of 3 years were tested for enterovirus-specific IgM in a mu capture enzyme-linked immunosorbent assay (ELISA). Enterovirus-specific IgM was detected in 45% samples from all age groups. In the 3-5-year age group, 67% specimens were positive. A notable male predominance (73%) was seen in the age group 0-15 years. As predicted, a seasonal increase in incidence was found in the summer and autumn months. Data from a questionnaire sent to the referring laboratories showed only a 5% enterovirus isolation rate from cerebrospinal fluids when isolation of a virus was attempted. The enterovirus IgM ELISA is a sensitive economical and rapid method for use in the diagnosis of viral meningitis.

Intrathecal synthesis of virus-specific oligoclonal antibodies in patients with enterovirus infection of the central nervous system

Cerebrospinal fluid (CSF) and serum samples from six patients with enterovirus infections were investigated by isoelectric focusing (IEF) and affinity-mediated immunoblot AMI) for the clonal distribution of entervirus-specific antibodies. In two patients with either acute meningitis or encephalitis and in one patient with a relapse of multiple sclerosis, oligoclonal IgG bands specific for enteroviruses were found predominantly in the CSF, revealing intrathecal synthesis of these antibodies. In three other patients with neurological symptoms probably unrelated to a current enterovirus infection, IEF and AMI disclosed nearly identical patterns of coxsackievirus-B-specific oligoclonal bands in the CSF and serum, indicating diffusion of these antibodies from the serum into the CSF. Although the number of patients in this study is small, the results suggest that intrathecally synthesized enterovirus-specific antibodies may be used as a means of identifying an enterovirus infection of the CNS.

Enterovirus IgM detection: specificity of mu-antibody-capture radioimmunoassays using virions and procapsids of Coxsackie B virus

A predominantly type-specific mu-capture radioimmunoassay (RIA) of IgM antibodies to Coxsackie B1-B5 (CB1-CB5) viruses was previously described (Frisk et al., 1984). The present study is concerned with the specificity of this assay, using as antigen different strains of one serotype (CB5) and procapsids of two serotypes (CB3 and CB5). Eight strains of CB5 virions were tested against acute and/or convalescent sera from 10 patients from whom CB5 had been isolated. Seven patients' sera were tested against their own strain. The frequency of IgM-positive patients varied from 9 of 10 (90%) to 5 of 10 (50%). In three cases the highest titres were obtained with the patients' own strain. When sera from patients with other enterovirus infections were tested against the CB5 strains, heterotypic titres were obtained to a certain extent (0-15.6%). The strains giving a high frequency of homotypic titres varied concerning heterotypic reactions. It is concluded that the choice of strain is important if a high frequency of homotypic titres with no or only a few heterotypic reactions is to be obtained. When procapsids were used as antigen, both homotypic and heterotypic titres were seen to a large extent. All patients with homotypic IgM against CB3 or CB5 virions showed IgM against the CB3 or the CB5 procapsids, respectively. When sera from patients with other enterovirus infections were tested, IgM was found in 54 of 93 patients (58%) with use of the CB3 procapsid and in 52 of 87 patients (60%) with the CB5 procapsid. It was often not the same patients who showed IgM against the two different procapsids. When both procapsids were used, IgM positivity was found in 62 of 81 patients (77%) with other enterovirus infections. It is concluded that the use of two or more procapsids in combination is of value for the diagnosis of a recent or current enterovirus infection.

Lansing poliovirus infection in mice: antibody demonstrable by enzyme-linked immunosorbent assay (ELISA) and immunoprecipitation but not by neutralization

Adult mice infected intracerebrally (i.c) with the Lansing strain of type 2 human poliovirus (HPV2) failed to develop a systemic neutralizing antibody response until 2 months post-infection (p.i). In contrast, an enzyme-linked immunosorbent assay (ELISA) demonstrated an antibody response of IgM and IgG classes beginning at day 1 p.i. with peak levels reached by 5 weeks p.i. This response was slightly greater in paralyzed than in nonparalyzed animals. Immunoprecipitation of poliovirus proteins from cytoplasmic extracts and disrupted purified virion preparations revealed antibodies to three capsid proteins, two capsid precursor proteins, and one nonstructural protein. Finally, neither neutralizing antibody nor definite virus replication was detected after oral, intraperitoneal, or intravenous routes of inoculation. We conclude that the lack of a systemic neutralizing antibody response in mice is probably due to an insufficient amount of infectious virus and consequently viral neutralizing epitopes reaching extraneural lymphoid tissues.

Rapid diagnosis of echovirus type 33 meningitis by specific IgM detection using an enzyme linked immunosorbent assay (ELISA)

During an outbreak of meningitis in France (in the Lyon area), from June to October 1982, serum and stool samples were collected from 227 patients. An enzyme-linked immunosorbent assay (ELISA) for titrating IgG and IgM antibodies anti-echovirus type 33 was developed and compared with the virus isolation technique, and with the titration of neutralizing antibodies. In 39 patients excreting echovirus 33 in faeces, the ELISA test allowed a positive serodiagnosis in 85% of the cases by detection of specific IgM (64% of the cases) and by seroconversion (21%). Compared with the neutralization (Nt) test, ELISA was found to be more sensitive. The antibody titres in ELISA were over 50 times higher and detected earlier than the neutralizing antibodies. This early immune response allowed a rapid diagnosis by specific IgM detection in the acute sera collected within 8 days after the appearance of the clinical symptoms in more than 50% of the 97 patients examined, whereas the Nt test allowed a positive serodiagnosis in only 32% of the patients. The use of a caesium chloride purified antigen insured the specificity of the reactions.

Reverse radioimmunoassays of IgM and IgG antibodies to Coxsackie B viruses in patients with acute myopericarditis

A reverse radioimmunoassay (RIA) of antibodies to enteroviruses, previously developed for the detection of IgM antibodies to Coxsackie B1 (CB1) and B3 (CB3) and to Echo 11 (E11) and 30 (E30) viruses, was extended in the present study for the detection of IgM antibodies to Coxsackie B2 (CB2), B4 (CB4), and B5 (CB5) viruses and of IgG antibodies to CB1-CB5, E11, and E30 viruses. After standardisation of the assays and application to a collection of serum specimens from patients with proven enterovirus infections, specimens from patients with diagnosed or suspected acute myo- and/or pericarditis (myopericarditis group), and control specimens from patients with nonenterovirus infections, were studied, as well as from apparently healthy subjects. Of the patients with enterovirus infections, 29 of 30 (97%) were positive in the IgM RIA and 19 of 25 (76%) in the IgG RIA. In the myopericarditis group, 18 of 37 (49%) patients showed Coxsackie B (CB) virus-specific IgM titres and 9 of 37 (24%) CB virus-specific IgG titres. In the control specimens very few positive responses were detected. The RIAs appeared to be type specific or at least predominantly type specific, provided that the amount of labeled virus was carefully standardised. The sensitivity of the RIAs seemed to be rather high for IgM but low for IgG. In the neutralisation (NT) test no significant rise or fall in titre against CB viruses was demonstrated in the myopericarditis group. It is concluded that the reverse IgM RIA may be valuable for studies of the role of CB viruses in acute myo- and/or pericarditis.

Indirect and reverse radioimmunoassays and their apparent specificities in the detection of antibodies to enteroviruses in human sera

Indirect radioimmunoassays (RIAs) of IgM and IgG antibodies to enteroviruses have been developed, using coxsackieviruses B1 and B3, and echoviruses 11 and 30. The titres of IgM and IgG were assayed in paired sera from patients infected with one of these viruses or coxsackieviruses A7, A9, A16, B2, B4, B5 or echoviruses 4, 17, or 25. Both IgM and IgG were found in almost all serum pairs with each of the four viruses used as an antigen, and there were no certain differences between titres obtained with homologous and heterologous antigens. The convalescent phase specimens contained significantly higher titres compared with the acute phase specimens, the difference being most pronounced for IgG. Of the specimens from patients with nonenterovirus infections, a relatively high percentage contained IgM and IgG against enterovirus antigen. However, no increases in titres were seen between acute and convalescent specimens. When specimens from younger patients, aged 2 days to 22 months, without evidence of enterovirus infections, were assayed with enterovirus antigen, the frequency of IgM titres was seen to increase with age. Almost all specimens from newborns were negative, whereas the specimens from 12- to 22-month-old children showed a high frequency of IgM titres. In specimens from patients aged 2 days to 8 months, the ratio between IgM and IgG titres increased with age, probably due to a loss of maternal IgG. The IgG titres in specimens from 8.5- to 22-month-old children were similar to the titres of specimens from the patients with nonenterovirus infections. A reverse IgM assay was also developed, using the same viruses and serum specimens as for the indirect assays. In contrast to the indirect IgM assay, the reverse IgM assay was apparently type specific, provided that the amount of labeled virus was carefully standardized. The reverse IgM RIA detected and identified antibody responses better than the neutralization test. Attempts to develop a reverse IgG assay were promising concerning the specificity, but the sensitivity was low.

Cross antigenicity among enteroviruses as revealed by immunoblot technique

Antigenic relationships of various human and two animal picornaviruses were investigated by the immunoblotting ("Western blot") technique. The viruses included all coxsackievirus B types (1-6), poliovirus types 1-3, several strains of echovirus 11, EMC virus, and FMDV. Antisera included human sera and sera from rabbits hyperimmunized with either purified picornaviruses, viral structural polypeptides (VP8), boiled or "sample-boiled" virions. Group-specific reactions of various extent were observed among the human picornaviruses, but not with EMC virus. These reactions were obtained with human sera (whole serum, IgG- and IgM-fraction) as well as with "monospecific" (neutralization test) rabbit antisera. Among cross reacting polypeptides VP1 was predominant with the notable exception of coxsackie B4, where VP1 (defined according to cleavage pattern) migrates in our gel system as second largest polypeptide. Antisera prepared vs VP1 had neutralizing activity as demonstrated with five different echovirus 11 strains (titers up to 2000). Antisera vs VP1 (and other VP8) exhibited cross-reactivity in the immunoblots. Antisera to the three poliovirus types (and to certain echovirus 11 strains) showed a surprisingly narrow cross-reacting spectrum which--in the case of poliovirus--could not be broadened by additional hyperimmunization of the rabbits with heated poliovirus 2. The significance of these results for a diagnostic ELISA in patients with picornavirus infections is dealt with.

Hemagglutinin-specific antibody responses in immunoglobulin G, A, and M isotypes as measured by enzyme-linked immunosorbent assay after primary or secondary infection of humans with influenza A virus

The isotype-specific antibody responses to purified hemagglutinin of adults undergoing either primary or secondary infection with an influenza A virus were characterized by using an enzyme-linked immunosorbent assay. Twenty-eight military recruits undergoing primary infection with A/USSR/92/77 (H1N1)-like virus had serum antibody rises in the immunoglobulin M (IgM) (86%), IgG (100%), and IgA (96%) isotypes. In contrast, 19 adult volunteers undergoing secondary infection with A/Peking/2/79 (H3N2) wild-type virus had serum antibody titer rises largely restricted to the IgG (68%) and IgA (74%) classes, with only 1 volunteer having a serum IgM antibody titer rise. Nasal wash hemagglutinin-specific antibody responses in the adults undergoing secondary infection were predominantly in the IgA class (74%). There was a correlation between the presence of and the magnitude of nasal wash and serum hemagglutinin-specific IgA antibody responses in these adults. This suggested that there was a common source for the hemagglutinin-specific local IgA antibody and serum IgA antibody produced after infection. The recruits undergoing primary H1N1 influenza virus infection had H1 hemagglutinin-specific enzyme-linked immunosorbent assay antibody in each of the IgA, IgG, and IgM isotypes in their acute-phase serum. However, no role for this cross-reactive antibody in modifying the severity of illness experienced by the recruits could be demonstrated.

Antibody capture radioimmunoassay (MACRIA) for coxsackievirus B4 and B5-specific IgM

An antibody capture radioimmunoassay was established for the detection of coxsackievirus B4 and B5-specific IgM. A significant feature of the assay was the use of an unrefined coxsackievirus B (CBV) antigen. The antigen was prepared by freeze thawing, ultrasonication and low speed centrifugation of infected Vero cells with no purification or concentration of the antigen being performed. Results of sera tested were expressed as a serum ratio (SR) by comparison with a low positive control serum. To establish an SR indicating positivity in the assays, 100 antenatal sera collected in late February were tested. The mean SR was calculated and the mean plus three standard deviations was taken as the minimum SR indicating positivity. Although resulting in a relatively insensitive assay, such a value was required to exclude sera giving a low level of reactivity which may be due to residual enterovirus-specific IgM resulting from a remote infection.The homologous CBV-IgM assay was positive in four cases of CBV4 infection and six cases of CBV5 infection. For the CBV4 IgM assay, ten of 20 (50%) sera from infections with CBV other than CBV4 were positive and nine of the 13 (69%) sera from infections with echoviruses or coxsackieviruses A were positive. Five of 18 (27%) sera with an elevated CBV neutralization titre were positive in the CBV4-IgM assay. For the CB5-IgM assay seven of 18 (39%) sera from infections with CBV other than CBV5 were positive and nine of 13 (69%) sera from infections with echoviruses or coxsackieviruses A were positive. The nine sera that were positive from this group in the CBV5-IgM assay were the same nine as were positive in the CBV4-IgM assay. Two of the 18 (11%) sera with an elevated CBV neutralization titre were positive in the CBV5-IgM assay. These two sera were also positive in the CBV4-IgM assay and had an elevated monotypic CBV4 neutralization titre. None of the sera giving positive results gave significant reactivity when tested with control antigen. Twelve rheumatoid factor containing sera and 46 sera from other infections were negative in both assays. Of 24 sera from confirmed CBV infection, seven gave a positive monotypic CBV4 or 5-IgM response, ten were positive in both assays and seven were negative in both assays. The positive results seen with sera from cases of heterologous enterovirus infection may result from an anamnestic IgM response or, more likely, IgM directed against enterovirus cross-reacting antigens. The absence of homologous neutralizing antibody at a dilution of 1:20 in nine of 20 sera that gave a positive CBV-IgM result and the presence of positive results for CBV4 and 5-IgM in a 14 month old infant who had echovirus 7 infection indicates that the IgM need not be directed against neutralizing antigens.Thus the CBV4 and 5-IgM assays developed appeared to be specific for an enterovirus infection but because of the cross-reactivity were not type-specific or group-specific.

Immunoglobulin M responses to the Norwalk virus of gastroenteritis

Eighty-seven serum specimens from 20 human subjects experimentally inoculated one or more times with Norwalk virus were quantitatively examined for virus-specific immunoglobulin M (IgM). A sensitive and specific radioimmunoassay for anti-Norwalk virus blocking activity was applied to whole serum and to separate IgM and IgG fractions obtained by sucrose density gradient ultracentrifugation. The peak IgM response occurred at about 2 weeks after illness, but IgM was detectable at lower titers for up to 21 weeks after infection. The IgM response was seen in volunteers who became ill, whether or not prechallenge total serum antibody was present. On long-term (27 to 42 months) rechallenge, volunteers who were previously ill and had produced IgM antibody again developed illness, and a secondary IgM response greater than the first was detected. Inoculated volunteers who did not develop illness, as well as previously ill volunteers on short-term rechallenge (4 to 14 weeks), usually failed to generate an IgM response, whether or not an IgG response had occurred. In ill subjects, the rise in IgM and IgG occurred concomitantly. Virus-specific IgM is not necessarily indicative of primary infection with Norwalk agent inasmuch as reinfection produces an enhancement of the IgM response. Furthermore, Norwalk-specific IgM responses do not appear to be associated with subclinical illness.

A modified absorption-reduction method to detect virus-specific hemagglutination inhibiting and neutralizing IgM antibodies

IgG antibodies are preferentially absorbed by protein A-coupled sepharose beads while most of the IgM and IgA antibodies remain in solution. Even relatively low amounts of virus-specific IgM antibodies can then be detected unequivocally by a decrease of the antibody titer following the treatment with reducing agents. Ethandithiol proved superior to 2-mercaptoethanol in combination with neutralization assays.