SPTLC2 and infection: To verify that VACV infection in wild type and Sptlc2-/- DC2.4 cells indeed relied on macropinocytosis, infection experiments were also performed in the presence of 3-indolepropionic acid (IPA-3), an inhibitor of p21-activated kinase 1 (PAK1) known to be required for macropinocytosis [48].