1, human U-87MG cells, human Calu-3 cells and human haematopoietic cancer cells was shown by the following findings to be required for mediating entry of pseudotyped viruses harboring H17 HAs [63] or H18 HAs [62] into a mammalian cell: (i) knockdown of HLA-DRA or HLA-DR α-chain or cell preincubation with an HLA-DRA-targeting antibody significantly reduced both H17- and H18-pseudotyped virus infections, (ii) ectopic expression of HLA-DR in non-susceptible cell lines rendered them susceptible to both H17- and H18-pseudotyped virus infections, (iii) expression of HLA-DR from other mammals, including different bat species, pigs and mice, or from chickens makes cells susceptible to H18-pseudotyped virus infection and (iv) intranasal infection of mice with H18N11 virus led to viral replication in the upper respiratory tracts of the mice.