Acid ceramidase of macrophages traps herpes simplex virus in multivesicular bodies and protects from severe disease

Macrophages have important protective functions during infection with herpes simplex virus type 1 (HSV-1). However, molecular mechanisms that restrict viral propagation and protect from severe disease are unclear. Here we found that macrophages take up HSV-1 via endocytosis and transport the virions into multivesicular bodies (MVBs). In MVBs, acid ceramidase (aCDase) converts ceramide into sphingosine and increases the formation of sphingosine-rich intraluminal vesicles (ILVs). Once HSV-1 particles pass MVBs, sphingosine-rich ILVs bind to HSV-1 particles, which restricts fusion with the limiting endosomal membrane and prevents cellular infection. Lack of aCDase in macrophage cultures or in Asah1–/– mice results in replication of HSV-1 and Asah1–/– mice died soon after systemic or intravaginal inoculation. The treatment of macrophages with sphingosine enhancing compounds blocks HSV-1 propagation, suggesting a therapeutic potential of this pathway. In conclusion, we demonstrate that aCDase loads ILVs with sphingosine, which prevents HSV-1 capsids from penetrating into the cytosol. 3 to 4 independent experiments were performed using different mice for isolation of macrophages and fibroblasts respectively.