Given the presence of bovine ApoE in the tissue culture medium that precluded accurate measurement of secreted mouse ApoE, expression of endogenous mouse ApoE was compared in mock- or MHV68-infected primary macrophages and MEFs that were treated with brefeldin A 18–24 hours post-infection to prevent protein secretion, followed by western analyses of cell lysates. The gene discussed is APOE; the disease is infection.