Identification of Past and Recent Parvovirus B19 Infection in Immunocompetent Individuals by Quantitative PCR and Enzyme Immunoassays: a Dual-Laboratory Study

Abstract

P arvoviruses (family Parvoviridae) are small (18-to 26-nm), nonenveloped, icosahedral viruses encapsidating a linear single-stranded DNA genome of approximately 5,000 nucleotides (1). Parvovirus B19, currently designated B19V, is a member of the family Parvoviridae, genus Erythrovirus (2). The B19V viral capsid has an icosahedral structure and is comprised of two proteins, VP1 (84 kDa) and VP2 (58 kDa). VP2 is the major protein (95% of the capsid composition) and contains receptor-and coreceptor-binding domains which together with self-assembly domains lead to the formation of highly stable particles (3). The minor capsid protein, VP1, differs from VP2 only in an N-terminal unique region (VP1u) composed of an additional 227 amino acids and has phospholipase A 2 (PLA 2 ) activity (4). VP1u elicits a dominant immune response (5).B19V infection in many instances is subclinical or presents as the mild and self-limiting fifth disease, or erythema infectiosum, typically manifesting as a "slapped cheeks" rash (6). Infection by B19V during pregnancy can result in several serious complications in the foetus, such as anemia, nonimmune hydrops, and ultimately intrauterine death (7). B19V is a potent inhibitor of hematopoiesis because it lytically infects erythroid progenitor cells (8), and in immunodeficient individuals, chronic B19V infection can result in chronic anemia (9). In individuals with underlying chronic hemolytic disorders, transient aplastic crisis following B19V infection can be a life-threatening complication (10). Finally, there is some evidence to suggest that B19V may infect other cell types, suggesting a possible involvement in the pathogenesis of a broad range of medical conditions, including idiopathic arthritis, vasculitis, meningoencephalitis, hepatitis, and myocarditis (11).Initially, the laboratory diagnosis of B19V infection was hampered by the lack of a cell culture system to grow the virus, necessitating the use of diagnostic tests lacking in sensitivity (12). Recently, recombinant DNA technology using prokaryotic (e.g., Escherichia coli) or eukaryotic (e.g., insect cells) expression systems has been applied to produce selected B19V antigens, in particular, VP1 and VP2. Prokaryotically expressed VP1/VP2 antigens undergo denaturation, and the antigen epitopes expressed are linear, whereas eukaryotic expression using baculovirus vectors generates empty capsids that are antigenically analogous to the native virus and include conformational epitopes. Assays using linear and those using conformational B19V VP1/VP2 can produce different results, leading to the general conclusion that conformational epitopes should be used for diagnostic purposes (13). Such assays need to be designed so that the presentation of conformational epitopes is optimized (14). Antibodies to linear VP2 epitopes are found mostly during acute infections and early convalescence, whereas those to conformational epitopes persist

Microsphere-Based IgM and IgG Avidity Assays for Human Parvovirus B19, Human Cytomegalovirus, and Toxoplasma gondii

“…Excellent agreement was seen between SIAs and reference assays for IgM (kappa coefficient 95% confidence interval [CI], 0.96 to 1) and for IgG avidity (kappa coefficient 95% CI, 0.91 to 1). In clarifying the B19 infection time, the new VP1u IgG avidity SIA also agreed well with the established EIA for the "conformation dependence" or "epitope type specificity" (ETS) of VP2 IgG, divergent qualitative determinants of antimicrobial IgG maturing progressively during the months since the first antigenic challenge (21,24,25). Of note, the three HCMV IgG avidity tests used in the current study (SIA, Architect, and Vidas) are technologically distinct: (i) while the SIA and Vidas are based on protein denaturation, Architect utilizes antigen competition (17), and (ii) while Vidas and Architect are based on single dilutions of serum (urea treated/reference), the SIA is based on the endpoint titration of serum (dilution series).…”

“…Combinations of serological tests are practicable for the detection of infections during pregnancy (20)(21)(22)(23). While IgM in general is a sensitive indicator of recent primary infection, in many contexts, it lacks clinical specificity, hence calling for additional markers for infection dating.…”

Extinct type of human parvovirus B19 persists in tonsillar B cells

“…The serostatus of the study subjects was determined with in-house B19V-IgG and -IgM EIAs as described4142. In brief, for the B19V-IgG EIA, 45 ng per well of biotinylated B19-VP2-VLPs were coated onto streptavidin coated plates using sample Diluent (#6111040, Anilabsystems, Finland).…”

“…B19V-IgM antibodies were measured using an in-house IgM capture EIA as described by Maple et al 42. Microtiter plate wells (Costar, Corning) were coated with goat anti-human IgM (#55097, Cappel/MP Biomedicals) and blocked with 3% bovine serum albumin.…”

The interaction between viral infections and immunosuppressed hosts is a challenging battle

“…in 1971 . Since then, it has been associated with nephropathy among renal transplant recipients and hemorrhagic cystitis among those receiving hematopoietic stem cell transplantation (HSCT) . BKV infects up to 90% of humans worldwide before the age of 10 years without specific signs or symptoms and remains latent thereafter.…”