The mechanisms underlying dengue hemorrhagic disease are incompletely understood. We previously showed that antidengue virus (DV) nonstructural protein 1 (NS1) Abs cross-react with human platelets and inhibit platelet aggregation. Based on sequence homology alignment, the cross-reactive epitopes reside in the C-terminal region of DV NS1. In this study, we compared the effects of Abs against full-length DV NS1 and NS1 lacking the C-terminal aa 271 to 352 (designated ΔC NS1). Anti-ΔC NS1 Abs exhibited lower platelet binding activity than that of anti-full-length NS1. Anti-full-length NS1 but not anti-ΔC NS1 Abs inhibited platelet aggregation, which was shown to involve integrin αIIbβ3 inactivation. We found that the bleeding time in full-length NS1-hyperimmunized mice was longer than that in the normal control mice. By contrast, ΔC NS1-hyperimmunized mice showed a bleeding time similar to that of normal control mice. Passively administered anti-DV NS1, but not anti-ΔC NS1, Ab level decreased markedly in serum and this decrease was correlated with Ab binding to platelets. A transient platelet loss in the circulation was observed after anti-DV NS1, but not anti-ΔC NS1, Ab administration. In summary, platelet dysfunction and bleeding tendency are induced by anti-full-length DV NS1 but not by anti-ΔC NS1 Abs. These findings may be important not only for understanding dengue hemorrhagic disease pathogenesis but also for dengue vaccine development.
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