Cross-reactions of immunoglobulin M and G antibodies with enterovirus-specific viral structural proteins

Detection of enterovirus-specific total and polymeric IgA antibodies in serum using a synthetic peptide or heated virion antigen in ELISA

The presence of enterovirus-specific total and polymeric IgA antibodies was assessed in serum from different groups of patients and healthy controls by indirect ELISA using heated virions and synthetic peptide, both enteroviral broad reactive antigens. Total IgA antibody response against a synthetic peptide, representing an enterovirus group-common epitope, was detected in 52% of the patients with an acute enterovirus infection and in 12% of the patients with other infections (P = 0.02). We also found a significant difference (P = 0.005) in the prevalence of peptide IgA antibodies between serum samples collected from blood donors during summer (20%), the prevalent season of enterovirus infections, and winter (6%). A polymeric IgA activity against the peptide was detected in only three patients with an enterovirus infection. In contrast, when a heated coxsackie B5 (coxB5) virus antigen was used, the prevalence of total serum IgA antibodies was not significantly different between patients with an acute enterovirus infection and patients with other infections (71% vs. 53% respectively; P = 0.3). Also no difference was found between the two groups of blood donors (47% in summer vs. 51% in winter; P = 0.7). However, the prevalence of serum polymeric IgA antibodies against coxsackie B5 antigen was significantly greater (P = 0.02) in patients with an acute enterovirus infection (57%) than in patients with other infections (18%). These findings suggest that the presence (18%). These findings suggest that the presence of total peptide-IgA or of polymeric coxsackie B5-IgA in serum is a specific marker of acute enterovirus infection. Finally, we show that the total peptide-IgA- and polymeric coxsackie B5-ELISAs may have a diagnostic value for the serodiagnosis of enterovirus infections when they are used in combination with enteroviral IgG-ELISA.

Identification of group-common linear epitopes in structural and nonstructural proteins of enteroviruses by using synthetic peptides

Synthetic peptides were employed in enzyme-linked immunosorbent assays to identify group-common linear epitopes in the structural and nonstructural proteins of enteroviruses. Nine linear epitopes were recognized by using sera from patients with heterotypic immunoglobulin G antibody responses to enterovirus infections. The most-reactive peptides were derived from conserved regions of the amino-terminal part of VP1, whereas peptides representing sequences from other conserved regions of VP1, as well as VP2, VP3, and VP4, and from a nonstructural region showed no or poor reactivity. These findings may be useful in the development of serological tests for the diagnosis of infections caused by a broad range of enteroviruses.

A method for detecting specific anti-C100 protein antibodies of IgM isotype in hepatitis C virus infection

A method for the determination of specific IgM antibodies to C100 protein, a hepatitis C virus-associated antigen, was developed which employed fractionation of serum proteins by gel chromatography and an enzyme-linked immunosorbent assay. Detection of IgM anti-C100 proved to be specific and reproducible in purified IgM fractions. Separation of IgM from IgG was necessary before IgM could be measured, because of the detrimental effect of the simultaneous presence of IgG antibodies with anti-C100 rectivity on IgM determination. IgM anti-C100 was not found in sera containing rheumatoid factors or IgM antibodies to other hepatotropic viruses. IgM anti-C100 was detected in 19 (44%) of 43 patients with hepatitis C virus-related chronic liver disease. When compared with the histological picture of liver disease, IgM anti-C100 was absent in patients with minimal changes and was most common (66.7%) in patients with progressive disease. It is suggested that IgM anti-C100 could reflect an active state of hepatitis C virus infection.

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.

Detection of immunoglobulin G, M, and A antibodies to enterovirus structural proteins by immunoblot technique in echovirus type 4-infected patients

Paired serum specimens from 24 patients with echovirus (EV) type 4 infection by virus isolation were tested by the immunoblot technique for the presence of IgG, IgM, and IgA antibodies to EV4 structural proteins. Single sera from 20 patients without neutralizing enterovirus IgM were used as controls. All the sera from EV4-infected patients had IgG antibodies to VP1 of EV4 but also 13 out of the 20 controls. 23 out of 24 EV4-infected patients elicited IgM and IgA specific antibodies to VP1, a pattern highly significant as compared with controls (3/20 for IgM and 8/20 for IgA). In 16 out of the 24 EV4-infected patients, the IgM antibodies were also directed against VP2 (versus 2 out of 20 in the control group). Anti-VP2 IgA were detected in 4 out of the 24 EV4 patients (versus 0 in controls). The 24 paired sera from EV4-infected subjects were also tested by immunoblot technique against three other enteroviruses: EV21, coxsackievirus A9 and poliovirus 1. Cross-reactivities were observed to a large extent against VP1 and VP2 proteins with the three classes of antibodies. These results confirm the data of previous studies on the reactivity of IgM antibodies to various structural proteins that IgG antibodies react exclusively to VP1. Furthermore, this study demonstrates the occurrence of circulating IgA antibodies directed to VP1 and sometimes VP2 in the course of enterovirus infection. The potential interest of this latter finding for diagnosis requires further investigation.