EHV-1 preferentially infects equine monocytes in peripheral blood mononuclear cells. Monocytes were enriched from equine PBMC using an anti-equine CD14 antibody and immunomagnetic beads. Monocyte-enriched (A, left panel) and -depleted (A, right panel) fractions of PBMC (5 × 105 cells) were infected for 24 h with RacL11N752-GFP (MOI of 1), then labeled with an A647-conjugated anti-CD14 antibody, after which 15 000 cells were analyzed for EHV-1 infection (GFP-positivity) by flow cytometry. Mock-infected monocyte-enriched fractions labeled with an A647-isotype antibody (B, left panel) or A647-conjugated anti-CD14 antibody (B, right panel) served as negative controls, with the isotype control being used to define the quadrants. Numbers in each quadrant represent percentage of total events. The majority of GFP-positive cells (upper and lower right quadrants) in EHV-1-infected monocyte-enriched and -depleted fractions are CD14-positive monocytes (upper right quadrant).