MARCO+ lymphatic endothelial cells sequester arthritogenic alphaviruses in the draining lymph node and limit viral dissemination

While viremia in the vertebrate host is a critical determinant of arboviral reservoir competency, transmission efficiency, and disease severity, immune mechanisms that control arboviral viremia are poorly defined. Here, we identify critical roles for the scavenger receptor MARCO in controlling viremia during arthritogenic alphavirus infections in mice. Following subcutaneous inoculation, alphavirus particles drain via the lymph and are rapidly captured by MARCO+ lymphatic endothelial cells (LECs) in the draining lymph node (dLN), limiting viral spread to the bloodstream. Upon reaching the bloodstream, MARCO-expressing Kupffer cells in the liver remove circulating alphavirus particles, limiting viremia and further viral dissemination. MARCO-mediated accumulation of alphavirus particles in the lymph node and liver has important implications as viremia and viral tissue burdens are elevated in MARCO-/- mice and disease outcomes are more severe. These findings uncover a previously unrecognized pathogen scavenging role for LECs and improve our mechanistic understanding of viremia control during arboviral infections. Overall design: Identification of cells harboring CHIKV RNA using single-cell RNA sequencing.