CLEC5A/MDL-1, a member of the myeloid C-type lectin family expressed on macrophages and neutrophils, is critical for dengue virus (DV)-induced hemorrhagic fever and shock syndrome in Stat1 −/− mice and ConA-treated wild type mice. However, whether CLEC5A is involved in the pathogenesis of viral encephalitis has not yet been investigated. To investigate the role of CLEC5A to regulate JEV-induced neuroinflammation, antagonistic anti-CLEC5A mAb and CLEC5A-deficient mice were generated. We find that Japanese encephalitis virus (JEV) directly interacts with CLEC5A and induces DAP12 phosphorylation in macrophages. In addition, JEV activates macrophages to secrete proinflammatory cytokines and chemokines, which are dramatically reduced in JEV-infected Clec5a−/− macrophages. Although blockade of CLEC5A cannot inhibit JEV infection of neurons and astrocytes, anti-CLEC5A mAb inhibits JEV-induced proinflammatory cytokine release from microglia and prevents bystander damage to neuronal cells. Moreover, JEV causes blood-brain barrier (BBB) disintegrity and lethality in STAT1-deficient (Stat1 −/−) mice, whereas peripheral administration of anti-CLEC5A mAb reduces infiltration of virus-harboring leukocytes into the central nervous system (CNS), restores BBB integrity, attenuates neuroinflammation, and protects mice from JEV-induced lethality. Moreover, all surviving mice develop protective humoral and cellular immunity against JEV infection. These observations demonstrate the critical role of CLEC5A in the pathogenesis of Japanese encephalitis, and identify CLEC5A as a target for the development of new treatments to reduce virus-induced brain damage.

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Background: CLEC18 is a novel C-type lectin not being characterized. Results: The amino acid residue in the C-type lectin-like domain of CLEC18 contribute to the differential glycan-binding ability. Conclusion: CLEC18 members are expressed in immune and non-immune cells, and preferentially bind to fucoidan, ␤-glucan, and galactan. Significance: The biochemical features, tissue distribution, and the glycan-binding specificity suggest that CLEC18 may contribute to host immunity against pathogens.