MDL-1/CLEC5A

MDL-1 (CLEC5A), also known as TREM-like transcript 1, is an activating C-type lectin receptor expressed on macrophages, dendritic cells, neutrophils, and osteoclasts. Unusual in this family, it lacks intrinsic signaling motifs and instead associates with the adaptor DAP12, coupling ligand binding to Syk-dependent activation. MDL-1 came to prominence when dengue virus was shown to engage it on myeloid cells, triggering cytokine release that drives hemorrhagic fever in mouse models; blocking antibodies proved protective. It also participates in osteoclast differentiation and in responses to other flaviviruses. Recombinant MDL-1/CLEC5A is used to study viral immunopathology, DAP12-coupled receptor signaling, and bone-immune interactions.