Type I interferon dampen platelet production and function.

RIVADENEYRA, LEONARDO; POZNER, ROBERTO G.; NEGROTTO, SOLEDAD; FONDEVILA, CARLOS; GOMEZ, RICARDO M; SCHATTNER, MIRTA

Amsterdam

Congreso; XXIV Congress of the International Society of Thrombosis and Haemostasis,; 2013

International Society of Thrombosis and Haemostasis,

Background: We have previously shown that infection of human CD34+ cells with Junin virus (arenavirus causative of Argentine hemorrhagic fever) or Poly(I:C), a synthetic double-stranded RNA that mimics viral replication, results in an impaired platelet production with no quantitative changes in megakaryocyte generation that was associated with the production of type I interferon (IFN-I). These findings identified IFN-I as a new regulator that selectively affects the last steps of megakaryocyte lifespan, and suggested a potential mechanism for thrombocytopenia in Argentine hemorrhagic fever and other diseases associated with increased type I IFN levels. Aim: To further analyze the megakaryocyte/platelet function abnormalities mediated by IFN-I and explore whether the levels of IFN-I produced during a viral infection are associated with quanti/qualitative alterations of thrombopoiesis. Methods: In-vitro: Cord blood human CD34+ cells were stimulated with thrombopoietin (50 ng/ml) and treated with different concentrations of Poly(I:C), strong inducer of IFN-I, or with human recombinant IFN-beta at day 7 of culture. After 14 days, CD61 expression and fibrinogen binding in platelets were evaluated by FACS. In-vivo: 8-10 week old C57BL/6 female mice were daily intravenously inoculated with Poly(I:C) (100 µg/mouse) and blood samples were taken at 24, 48 and 72 hours. Platelet count was determined with a veterinary cell counter. P-selectin expression and fibrinogen binding in peripheral platelets were evaluated by FACS. Plasmatic IFN-beta levels were determined by ELISA. Results represent the mean±SEM of 5-6 experiments. Results: While the number of CD61 copies on the membrane of in-vitro-generated platelets after Poly(I:C) or IFN-I treatment was similar to control samples, fibrinogen binding of thrombin-stimulated platelets was significantly inhibited (85% and 69% of maximal inhibition respectively, IC50: 6.5 mg/ml and 7.6 U/ml for Poly(I:C) and IFN-I respectively). When mice were inoculated with Poly(I:C), a reduction of 28, 54 and 67% in the platelet count was observed at 24, 48 and 72 hours respectively. The mean platelet volume was 8 and 13% higher than control values at 48 and 72 hours respectively (p<0.01), indicating a slight but significant bone marrow response to the decreased platelet count. While thrombin-induced fibrinogen binding and P-selectin externalization of platelets from mice that were treated for 24 or 48 hours with Poly(I:C) were not different from control animals, both responses were significantly reduced after 72 hours (complete turnover of the platelet population) (51 and 33% lower than the control value respectively, p<0.05) suggesting an inhibitory effect at the bone marrow level rather than an effect on peripheral platelets. The IFN-beta levels in plasma from treated animals were significantly higher than those found in controls (89±19, 101±26, 126±21 pg/ml at 24, 48 and 72 hours respectively, vs. 41±9). Conclusions: Our data suggest that treatment of mice with Poly(I:C) inhibits platelet generation and function associated with an increase in the levels of plasmatic IFN-I.These findings were also supported by the in-vitro data in human cells and may explain the defects observed in platelet production/function as a consequence of viral infections.