Differential IgM response to conformational and linear epitopes of parvovirus B19 VP1 and VP2 structural proteins

Abstract

The IgM immune response against conformational and linear epitopes of B19 structural proteins VP1 and VP2 was examined in serum samples with a suspect B19 infection to determine the most suitable antigen for use in IgM detection and also to evaluate a possible relationship between the course of B19 infection and the presence of epitope type-specific IgM. The detection of IgM against conformational epitopes was performed by ELISA using undenatured VP1 and VP2 antigens whereas the detection of IgM against linear epitopes was performed by Western blot assays using denatured VP1 and VP2. IgM immune response against VP1 conformational epitopes appeared dominant, being detected in all serum samples positive for specific IgM, whereas IgM against VP2 linear antigen were found less frequently, being identified in less than half of the B19 IgM positive sera. In the examination of the course of infection, IgM against VP1 conformational epitopes appeared in the active phase of B19 infection at the same time and with the same frequency as IgM anti VP2 conformational epitopes and anti linear VP1 epitopes. IgM against VP1 conformational epitopes were seen to be long-lasting because in the recent phase of infection they were still present when other specific IgM were absent. During the active phase of B19 infection, IgM against VP2 linear epitopes were less frequently found than other specific IgM and in the recent phase they underwent a rapid temporal diminution. The data demonstrate that a sensitive B19 IgM test needs to be performed in diagnostic laboratories by ELISA using conformational B19 antigens; Western blot assays can be used only as confirmatory tests using VP1 linear antigens.

Reactivity of Genotype-Specific Recombinant Proteins of Human Erythrovirus B19 with Plasmas from Areas Where Genotype 1 or 3 Is Endemic

“…It was previously reported that the antigenicity of the capsids containing VP1-2 proteins is different from that of the VP2-only capsids (28). Similarly, there were reports indicating that some samples might react with VP2-only capsids but not with VP2 capsids containing VP1 and vice versa (19)(20)(21). Although there might be differences in the antigenicity of VP1-2 and VP2-only capsids, they might be minor and not lead to significant changes in the overall reactivity of the antibody pool comprised of antibodies to multiple epitopes present in the capsid proteins.…”

Identification and Characterization of Persistent Human Erythrovirus Infection in Blood Donor Samples

“…Several VP2 and VP1u regions containing neutralizing epitopes have been identified (10, 32, 43). However, neutralizing linear epitopes seem to cluster in the N terminus of VP1u and the VP1-VP2 junction regions and to elicit a more efficient response than the epitopes in the VP2 region, which are mainly conformational epitopes (21,26,28,31,36). The inability to develop an efficient neutralizing immune response, as observed mainly in immunosuppressed individuals but also in otherwise healthy individuals, may result in the failure to eliminate the virus, thus leading to persistent infection and the possible occurrence of chronic diseases, such as chronic anemia or arthropathies (14).…”

Comparison of Three Commercially Available Serologic Assays Used To Detect Human Parvovirus B19-Specific Immunoglobulin M (IgM) and IgG Antibodies in Sera of Pregnant Women

“…Circulating antibodies recognize both linear and conformational epitopes of the capsid proteins. Numerous investigators have demonstrated that B19V-specific IgG antibodies recognizing linear epitopes disappear around 6 months after infection, leaving only circulating antibodies that recognize conformational epitopes (4,7,15,17,20). Therefore, the nature of the viral antigen(s) used in the B19V-specific serologic assay is an important variable to consider in evaluating analytical test performance.…”