Epitope Type-Specific IgG Responses to Capsid Proteins VP1 and VP2 of Human Parvovirus B19

Abstract

Temporal reactivities of IgG towards native and linear antigenic determinants in assembled capsids or isolated structural proteins of human parvovirus B19 were measured by an epitope type-specific IgG EIA and by immunoblots. Antigens used were baculovirus-expressed B19 capsids composed of the proteins VP1 and VP2 in their native proportion, VP2 alone, or a prokaryotic VP1 fusion protein. Follow-up sera after primary infection were compared with samples from previously infected persons. The IgG responses during acute and early convalescence phases were directed towards both conformational and linear epitopes of VP2. The antibodies against the linear VP2 epitopes disappeared abruptly within 6 months; however, the conformational VP2 antibodies persisted. The epitope type-specific IgG reactivity of VP1 was strikingly different from that of VP2. On the basis of these results, two novel tests were developed for patient diagnosis. Both tests are suitable for verifying the time of human parvovirus infection.

B Cell Memory Is Directed toward Conformational Epitopes of Parvovirus B19 Capsid Proteins and the Unique Region of VP1

“…It is also likely that the B19-specific B cell ELISpot assay could find application in the confirmation of past infection with B19. It is well established that the humoral immune response to B19 evolves gradually, from a population of antibodies with reactivity against both linear and conformational epitopes to one with predominantly conformational-epitope specificity [8,9,23,24]. In the present study, although only 5 individuals exhibited, by either microplate immunoassay or Western blot, IgG reactivity against VP1-D, 12 individuals displayed a positive B cell-memory response against the unique region of VP1.…”

“…The latter 2 proteins, which compose the viral capsid (5% VP1; 95% VP2), are colinear, except that VP1 contains a 227-residue aminoterminal extension (hereafter, "unique region"), compared with VP2 [5]. A transient, high viremia is observed in individuals after infection with B19, followed by the development, within a number of days, of B19-specific IgM [6]; within a number of weeks, the presence of B19-specific IgG directed against linear and conformational epitopes of viral capsid proteins VP1 and VP2, in addition to the presence of IgG directed against NS1, is evident [3,7,8]. B19 infection leads to an intriguing immunological phenomenon-a specific loss of IgG, initially reactive against linear epitopes of VP1 and VP2, occurs after infection [8,9].…”

“…B19 infection leads to an intriguing immunological phenomenon-a specific loss of IgG, initially reactive against linear epitopes of VP1 and VP2, occurs after infection [8,9]. In fact, specific IgG against linear epitopes of VP2 disappears within 6-12 months after infection [8]. More dramatically, there is a near-total diminution of NS1-specific IgG in previously infected individuals [10].…”

“…It is, therefore, firmly established that detection of B19-specific IgG against conformational epitopes is currently the most reliable method for the detection of previous infection with, and probable immunity to, B19. However, the reason for the postinfection loss of IgG reactivity against linear epitopes of B19 capsid proteins has not yet been elucidated, and few mechanisms that would explain this loss have been suggested [8].…”

Anti-VP1 and anti-VP2 antibodies detected by immunofluorescence assays in patients with acute human parvovirus B19 infection

“…The kinetics of epitope type (linear/conformational) specificity in human parvovirus B19 antibody responses were studied by Söderlund et al (1995b) using recombinant viral capsids as antigen. IgG antibodies of acutely infected patients recognized both conformational and linear antigenic determinants of VP2.…”