CD9 and infection: Earlier report has documented the intracellular expression of CD63 by fluorescence microscopy and suggested that upon infection with the pathogen, endogenous CD63, as well as, CD9 and CD81 were recruited to the bacterial entry site, though finally only CD81 was required for bacterial internalization, identifying for the first time the role of tetraspanins in L. monocytogenes entry into target cells [56].