Induction of antiphospholipid antibodies and antiphospholipid syndrome-like autoimmunity in naive mice with antibody against human parvovirus B19 VP1 unique region protein

Background: Previous studies have postulated a connection between human parvovirus B19 (B19) infection and anti-phospholipid antibodies (APhL). B19 infection and anti-phospholipid syndrome (APS) exhibit congruent symptoms. Recently, phospholipase A2 (PLA2)-like activity has been linked to the VP1 unique region (VP1u) of B19. However, the precise role of B19-VP1u in pathogenesis of autoimmunity is still obscure. Methods: To elucidate the roles of VP1u in B19 infection and autoimmunity, the reactivity of B19-VP1u proteins with various autoantibodies were evaluated by ELISA and immunoblotting. Rabbits were immunized with purified recombinant B19-VP1u protein to generate anti-sera. Absorption experiments were conducted to determine the binding specificity of rabbit anti-sera against B19-VP1u, cardiolipin (CL) and β-2-glycoprotein I (β2GPI). Moreover, the effects of passive transfer of polyclonal rabbit anti-B19-VP1u IgG antibodies on platelets, activated partial thromboplastin time (aPTT), and autoantibodies were assessed. Results: Autoantibodies against CL, β2GPI, and phospholipid (PhL) in sera from patients with B19 infection, were cross-reactive with B19-VP1u. Consistently, sera from rabbits immunized with recombinant B19-VP1u protein displayed raised detectable immunoglobulins against B19-VP1u, CL, β2GPI and PhL. Additionally, the mice immunized with anti-B19-VP1u IgG developed thrombocytopenia, prolongation of aPTT, and autoantibody against β2GPI and PhL. Conclusions: These experimental results suggested the association between B19-VP1u and production of anti-β2GPI antibodies, APhL, and APS-like autoimmunity. Altogether, it may provide a clue in understanding the role of B19-VP1u in inducing autoantibodies and B19-associated APS manifestations.