Aspects moléculaires et spécificités fines des auto-anticorps antiphospholipides (contribution à la compréhension de leur origine et de leur pathogénicité)

STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

The globoside receptor triggers structural changes in the B19V capsid that facilitate virus internalization

Globoside (Gb4Cer), Ku80 autoantigen, and α5β1 integrin have been identified as cell receptors/coreceptors for human parvovirus B19 (B19V), but their role and mechanism of interaction with the virus are largely unknown. In UT7/Epo cells, expression of Gb4Cer and CD49e (integrin alpha-5) was high, but expression of Ku80 was insignificant. B19V colocalized with Gb4Cer and, to a lesser extent, with CD49e. However, only anti-Gb4Cer antibodies could disturb virus attachment. Only a small proportion of cell-bound viruses were internalized, while the majority became detached from the receptor. When added to uninfected cells, the receptor-detached virus showed superior cell binding capacity and infectivity. Attachment of B19V to cells triggered conformational changes in the capsid leading to the accessibility of the N terminus of VP1 (VP1u) to antibodies, which was maintained in the receptor-detached virus. VP1u became similarly accessible to antibodies following incubation of B19V particles with increasing concentrations of purified Gb4Cer. The receptor-mediated exposure of VP1u is critical for virus internalization, since capsids lacking VP1 could bind to cells but were not internalized. Moreover, an antibody against the N terminus of VP1u disturbed virus internalization, but only when present during and not after virus attachment, indicating the involvement of this region in binding events required for internalization. These results suggest that Gb4Cer is not only the primary receptor for B19V attachment but also the mediator of capsid rearrangements required for subsequent interactions leading to virus internalization. The capacity of the virus to detach and reattach again would enhance the probability of productive infections

Molecular mechanism underlying B19 virus inactivation and comparison to other parvoviruses

BACKGROUND: B19 virus (B19V) is a human patho-gen frequently present in blood specimens. Transmis-sion of the virus occurs mainly via the respiratory route,but it has also been shown to occur through the admin-istration of contaminated plasma-derived products.Parvoviridaeare highly resistant to physicochemicaltreatments; however, B19V is more vulnerable than therest of parvoviruses. The molecular mechanism govern-ing the inactivation of B19V and the reason for itshigher vulnerability remain unknown. STUDY DESIGN AND METHODS: After inactivation ofB19V by wet heat and low pH, the integrity of the viralcapsid was examined by immunoprecipitation with twomonoclonal antibodies directed to the N-terminal of VP1and to a conformational epitope in VP2. The accessibil-ity of the viral DNA was quantitatively analyzed bya hybridization-extension assay and by nucleasetreatment. RESULTS: The integrity of the viral particles was main-tained during the inactivation procedure; however, thecapsids became totally depleted of viral DNA. TheDNA-depleted capsids, although not infectious, wereable to attach to target cells. Comparison studies withother members of theParvoviridaefamily revealed aremarkable instability of B19V DNA in its encapsidatedstate. CONCLUSION: Inactivation of B19V by heat or low pHis not mediated by capsid disintegration but by the con-version of the infectious virions into DNA-depletedcapsids. The high instability of the viral DNA in itsencapsidated state is an exclusive feature of B19V,which explains its lower resistance to inactivationtreatments