Bacterial infection-associated improvement of platelet counts in two patients with chronic and unresponsive idiopathic thrombocytopenic purpura with normal platelet survival studies

Gammaherpesvirus latency induces antibody-associated thrombocytopenia in mice

Human herpesviruses establish lifelong latency. Viral recrudescence can lead to the development of cancers, immunoproliferative disorders, transplantation complications, and thrombocytopenia. Although platelet-specific autoantibodies have been reported in patients infected with the Epstein-Barr virus (EBV), the mechanisms by which thrombocytopenia is induced remain unclear, as do the relative contributions of lytic viral replication and latent viral gene expression. The human gammaherpesviruses are tightly restricted in their ability to infect other mammals, so they are difficult to study in live animal models. Here we show that infection of mice with murine gammaherpesvirus-68 (γHV68), a rodent-specific pathogen closely related to EBV, induces the production of platelet-binding antibodies and causes thrombocytopenia. Infection of antibody-deficient mice does not lead to thrombocytopenia, indicating the platelet decrease is mediated by antibody. Additionally, infection with a latency-null recombinant γHV68 does not induce thrombocytopenia, suggesting factors associated with viral latency drive the infection-induced antibody-mediated thrombocytopenia. These studies describe an important animal model of gammaherpesvirus-induced autoimmune thrombocytopenia and demonstrate that this pathology is mediated by antibody and dependent on viral latency. This model will allow studies of the underlying mechanisms of disease progression and the testing of therapeutic strategies for the alleviation of virus-induced thrombocytopenia.

Effects of interferon-alpha therapy on immune parameters in immune thrombocytopenic purpura

Interferon-alpha (IFN alpha) has been shown to increase platelet numbers in patients with immune thrombocytopenic purpura (ITP), but the basis for this effect is not known. In this study changes in immune function were monitored following administration of IFN alpha to seven patients whose ITP had proved refractory to conventional therapy. Patients' peripheral blood mononuclear cells were cultured with phytohaemagglutinin and culture supernatants assayed for cytokine production. Production of the Th1 cytokines IL-2 and IFN-gamma was low in patients compared to healthy controls, and amounts of these tended to increase after IFN alpha therapy. In two patients high levels of IL-10 were detectable in culture, and these were reduced after IFN alpha. In patients who had high serum concentrations of IL-4 or IL-10, these were also decreased following therapy. Natural killer cell activity, which was low in the patients prior to therapy, was increased following administration of IFN alpha. In those patients with detectable platelet-associated autoantibody to gpIIb/IIIa, the amounts were reduced after treatment. Two patients had an unusually high percentage of T cells expressing the gamma delta T cell receptor, which decreased after therapy. The findings are consistent with an increase in Th 1 activity and a decrease in autoantibody production following IFN alpha therapy, which may be related to the beneficial effects of this cytokine.