TFRC and infection: Other evidence for one or more receptor(s) other than TfR1 mediating the infection of non-heterologous cells includes the finding that although the Crandell feline kidney cell line (CrFK) is well known to be susceptible to MMTV [11,12], the transfer of the feline TfR1 to other cells does not make cells susceptible to MMTV infection [13].