Gangliosides are not essential for influenza virus infection

Sialic acid is known to be an essential part of influenza virus receptors, but the specific identity of the receptor molecules on target cells is still not defined. In particular, the relative roles played by cellular sialylglycoproteins and gangliosides in virus entry into target cells remain unclear. To test whether gangliosides are essential for virus infection, we used the GM-95 mutant cell line of mouse B16 melanoma which lacks synthesis of major glycosphingolipids including gangliosides. We found that GM-95 cells grown in serum-containing medium harboured substantial amounts of ganglioside receptors for influenza virus due to incorporation of serum gangliosides. To obtain ganglioside-free cells, we adapted GM-95 cells to growth in defined serum-free (sf) medium. Ganglioside-free GM-95-sf cells could be infected by avian and human influenza A viruses and produced infectious virus progeny demonstrating that gangliosides were neither absolutely necessary for the early nor for the late stages of the infection. However, sensitivity of the GM-95-sf cells to the viruses was 2-4 times lower than that of the ganglioside-containing parent cell line. Further studies are needed to specify whether this effect was due to the lack of gangliosides, neutral glycosphingolipids, or other effects.