SAMHD1 and infection: It is known that macrophages exhibit low permissiveness to infection, in part due to the constitutive expression of the antiviral restriction factor sterile alpha motif (SAM) domain- and histidine/aspartic acid (HD) domain-containing protein 1 (SAMHD1), a deoxynucleoside triphosphate (dNTP) triphosphohydrolase that restricts HIV-1 by maintaining dNTP concentrations below the threshold required for efficient reverse transcription (6, –, 9).