The parvoviruses use the TfR to bind to, enter, and infect cells, and analysis of the TfRs from different hosts showed that the variation in the apical domain of the receptor determined the specific interaction with the capsid. Looking at the specific interactions of the feline, canine, and raccoon TfRs with the capsids of viruses from different hosts shows that those differ between different viruses and mutant forms of the TfR, and are key determinants of host range.