NGC 4921 could have had its hydrogen stripped from it through interaction with the intergalactic medium (IGM). IGM is rarefied ionised plasma which surrounds and stretches between galaxies. The stripping of hydrogen gas occurs mostly within clusters of galaxies and there were 73 objects found near (within 750 kpc and 500 km/s) NGC 4921, part of the Coma cluster, which justifies the likeliness of NGC 4921 losing its hydrogen through IGM interaction. Another example is the Virgo Supercluster, where H1 deficiency is widely present.