Parvovirus B19 uptake is a highly selective process controlled by VP1u, a novel determinant of viral tropism

The VP1 unique region (VP1u) of human parvovirus B19 (B19V) is the immunodominant part of the viral capsid. Originally inaccessible, the VP1u becomes exposed upon primary attachment to the globoside receptor. To study the function of the exposed VP1u in B19V uptake, we expressed this region as a recombinant protein. Here, we report that purified recombinant VP1u binds and is internalized in UT7/Epo cells. By means of truncations and specific antibodies, we identified the most N-terminal amino acid residues of VP1u as the essential region for binding and internalization. Furthermore, the recombinant VP1u was able to block B19V uptake, suggesting that the protein and the virus undertake the same internalization pathway. Assays with different erythroid and nonerythroid cell lines showed that the N-terminal VP1u binding was restricted to a few cell lines of the erythroid lineage, which were also the only cells that allowed B19V internalization and infection. These results together indicate that the N-terminal region of VP1u is responsible for the internalization of the virus and that the interacting receptor is restricted to B19V-susceptible cells. The highly selective uptake mechanism represents a novel determinant of the tropism and pathogenesis of B19V.

Impaired genome encapsidation restricts the in vitro propagation of human parvovirus B19.

The lack of a permissive cell culture system hampers the study of human parvovirus B19 (B19V). UT7/Epo is one of the few established cell lines that can be infected with B19V but generates none or few infectious progeny. Recently, hypoxic conditions or the use of primary CD36+ erythroid progenitor cells (CD36+ EPCs) have been shown to improve the infection. These novel approaches were evaluated in infection and transfection experiments. Hypoxic conditions or the use of CD36+ EPCs resulted in a significant acceleration of the infection/transfection and a modest increase in the yield of capsid progeny. However, under all tested conditions, genome encapsidation was impaired seriously. Further analysis of the cell culture virus progeny revealed that differently to the wild-type virus, the VP1 unique region (VP1u) was exposed partially and was unable to become further externalized upon heat treatment. The fivefold axes pore, which is used for VP1u externalization and genome encapsidation, might be constricted by the atypical VP1u conformation explaining the packaging failure. Although CD36+ EPCs and hypoxia facilitate B19V infection, large quantities of infectious progeny cannot be generated due to a failure in genome encapsidation, which arises as a major limiting factor for the in vitro propagation of B19V.

Cryo-electron microscopy studies of empty capsids of human parvovirus B19 complexed with its cellular receptor.

The three-dimensional structures of human parvovirus B19 VP2 capsids, alone and complexed with its cellular receptor, globoside, have been determined to 26 resolution. The B19 capsid structure, reconstructed from cryo-electron micrographs of vitrified specimens, has depressions on the icosahedral 2-fold and 3-fold axes, as well as a canyon-like region around the 5-fold axes. Similar results had previously been found in an 8 angstrom resolution map derived from x-ray diffraction data. Other parvoviral structures have a cylindrical channel along the 5-fold icosahedral axes, whereas density covers the 5-fold axes in B19. The glycolipid receptor molecules bind into the depressions on the 3-fold axes of the B19:globoside complex. A model of the tetrasaccharide component of globoside, organized as a trimeric fiber, fits well into the difference density representing the globoside receptor. Escape mutations to neutralizing antibodies map onto th capsid surface at regions immediately surrounding the globoside attachment sites. The proximity of the antigenic epitopes to the receptor site suggests that neutralization of virus infectivity is caused by preventing attachment of viruses to cells.

Parvovirus B19 promoter at map unit 6 confers autonomous replication competence and erythroid specificity to adeno-associated virus 2 in primary human hematopoietic progenitor cells.

The pathogenic human parvovirus B19 is an autonomously replicating virus with a remarkable tropism for human erythroid progenitor cells. Although the target cell specificity for B19 infection has been suggested to be mediated by the erythrocyte P-antigen receptor (globoside), a number of nonerythroid cells that express this receptor are nonpermissive for B19 replication. To directly test the role of expression from the B19 promoter at map unit 6 (B19p6) in the erythroid cell specificity of B19, we constructed a recombinant adeno-associated virus 2 (AAV), in which the authentic AAV promoter at map unit 5 (AAVp5) was replaced by the B19p6 promoter. Although the wild-type (wt) AAV requires a helper virus for its optimal replication, we hypothesized that inserting the B19p6 promoter in a recombinant AAV would permit autonomous viral replication, but only in erythroid progenitor cells. In this report, we provide evidence that the B19p6 promoter is necessary and sufficient to impart autonomous replication competence and erythroid specificity to AAV in primary human hematopoietic progenitor cells. Thus, expression from the B19p6 promoter plays an important role in post-P-antigen receptor erythroid-cell specificity of parvovirus B19. The AAV-B19 hybrid vector system may also prove to be useful in potential gene therapy of human hemoglobinopathies.

Parvovirus B19 infection presenting as 'bathing trunk' erythema with pustules

A 7-year-old girl presented with acute vulval erythema and pustules, associated with a petechial eruption in her flexures and over her feet. There was a mild prodromal illness and the patient was afebrile. There were minimal symptoms associated with the rash. Skin and throat swabs were negative and blood examination showed mild neutrophilia and lymphopaenia. Parvovirus B19 IgM was detected on serology and cutaneous features resolved within 4 days. This is a further case of parvovirus B19 infection presenting as a 'bathing trunk' exanthem that has unique dermatologic features, including the presence of pustules and distant petechiae. © 2006 The Australasian College of Dermatologists.

Immunologic Storm Simulating Systemic Lupus Erythematosus Following Parvovirus B19 Infection

Background: The appearance of symptoms compatible with systemic autoimmune diseases has been described in relation to several viral infections like HIV, cytomegalovirus and especially PVB19, depending on the evolution of the immunological condition of the host and their age. We present a young immunocompetent male patient, with clinical manifestations simulating systemic lupus erythematosus (SLE) with important activation of cytokines. Methods: For quantification of the different cytokines in plasma, a commercially available multiplex bead immunoassay, based on the Luminex platform (Cat # HSCYTO-60SK-08, Milliplex® MAP High Sensitivity, Millipore), was used according to the manufacturer’s instructions. All samples were run in duplicate and the data (mean fluorescence intensity) were analyzed using a Luminex reader. The mean concentration was calculated using a standard curve. Results: The clinical evolution was favourable without the need for any specific treatment, showing complete recovery after two months. Whilst the symptoms and viral charge were disappearing, the anti-DNA continued to increase and we demonstrate important activation of IL-10, IL-6 and TNFα cytokines as a result of a hyperstimulating response by an immunocompetent hyperfunctional system, which persists after clinical improvement. We should emphasize the behaviour of two cytokines: IL-12p70 and IL-2, which showed opposite tendencies. Conclusions: Viral infections, especially PVB19, can produce or simulate several autoimmune diseases as a hyperstimulation response from an immunocompetent hyperfunctional system. Consequently, a persistent increase of autoantobodies and important activation of cytokines, even after clinical improvement and seroconversion, can be demonstrated.

Human parvovirus infections during pregnancy : Special reference to the child-care employees

Human parvovirus B19 (B19V) is known to cause anemia, hydrops fetalis, and fetal death especially during the first half of pregnancy. Women who are in occupational contact with young children are at increased risk of B19V infection. The role of the recently discovered human parvovirus, human bocavirus (HBoV), in reproduction is unknown. The aim of this research project was to establish a scientific basis for assessing the work safety of pregnant women and for issuing special maternity leave regulations during B19V epidemics in Finland. The impact of HBoV infection on the pregnant woman and her fetus was also defined. B19V DNA was found in 0.8% of the miscarriages and in 2.4% of the intrauterine fetal death (IUFD; fetal death after completed 22 gestational weeks). All control fetuses (from induced abortions) were B19V-DNA negative. The findings on hydropic B19V DNA-positive IUFDs with evidence of acute or recent maternal B19V infection are in line with those of previous Swedish studies. However, the high prevalence of B19V-related nonhydropic IUFDs noted in the Swedish studies was mostly without evidence of maternal B19V infection and was not found during the third trimester. HBoV was not associated with miscarriages or IUFDs. Almost all of the studied pregnant women were HboV-IgG positive, and thus most probably immune to HBoV. All preterm births, perinatal deaths, smallness for gestational age (SGA) and congenital anomaly were recorded among the infants of child-care employees in a nationwide register-based cohort study over a period of 14 years. Little or no differences in the results were found between the infants of the child-care employees and those of the comparison group. The annual B19V seroconversion rate was over two-fold among the child-care employees, compared to the women in the comparison group. The seropositivity of the child-care employees increased with age, and years from qualification/joining the trade union. In general, the child-care employees are not at increased risk for adverse pregnancy outcome. However, at the population level, the risk of rare events, such as adverse pregnancy outcomes attributed to infections, could not be determined. According to previous studies, seronegative women had a 5 10% excess risk of losing the fetus during the first half of their pregnancy, but thereafter the risk was very low. Therefore, an over two-fold increased risk of B19V infection among child-care employees is considerable, and should be taken into account in the assessment of the occupational safety of pregnant women, especially during the first half of their pregnancy.

Evolution of microstructure and texture in Ni49.4Ti38.6Hf12 shape memory alloy during hot rolling

This paper deals with the evolution of microstructure and texture during hot rolling of hafnium containing NiTi based shape memory alloy Ni49.4Ti38.6Hf12. The formation of the R-phase has been associated with the precipitation of (Ti,Hf)(2)Ni phase. The crystallographic texture of the parent phase B2 as well as the product phases R and B19' have been determined. It has been found that the variant selection during the B2 -> R phase transformation is quite strong compared to the case of the B2 -> B19' transformation. During deformation, the texture of the austenite phase evolves with strong Goss and Bs components. After transformation to martensitic structure, it gives rise to a 011]parallel to RD fiber. Microstructure and texture studies reveal the occurrence of partial dynamic recrystallization during hot rolling. Large strain heterogeneities that occur surrounding (Ti,Hf)(2)Ni precipitates are relieved through extended dynamic recovery instead of particle stimulated nucleation.

Evolution and stability of phases in a high temperature shape memory alloy Ni49.4Ti38.6Hf12

Ni49.4Ti38.6Hf12 shape memory alloy has been characterized for structure, microstructure and transformation temperatures. The microstructure of the as-cast sample consists of B19' and R-phases, and (Ti,Hf)(2)Ni precipitate phase along the grain boundaries in the form of dendrites. The microstructure of the solution treated sample contains only B19' martensite phase, whereas a second heat treatment after solutionizing results in reappearance of the R-phase and the (Ti,Hf)(2)Ni grain boundary precipitate phase in the microstructure. A detailed microstructural examination shows the presence of precipitates having both coherent and incoherent interface with the matrix, the type of interface being dictated by the crystallographic orientation of the matrix phase. The present study shows that the (Ti,Hf)(2)Ni precipitates having coherent interface with the matrix, drive the formation of the R-phase in the microstructure. (C) 2013 Elsevier Ltd. All rights reserved.