N-glycosylation contributes to the limited cross-reactivity between hemagglutinin neuraminidase proteins of human parainfluenza virus type 4A and 4B

cDNAs encoding human parainfluenza virus type 4B (hPIV4B) hemagglutinin neu raminidase (HN) protein were cloned and the nucleotide sequences were deter mined. A high degree of identity (81.4%) was observed between the nucleotid e sequences of hPIV-4A and -4B HN proteins, and an 87.3% identity was found between the deduced amino acid sequences. This degree of identity is consi dered to be greater than immunological similarity between hPIV-4A and -4B H N proteins determined using monoclonal antibodies. To elucidate the causes of the antigenic difference between HN proteins of hPIV-4A and -4B, we cons tructed three cDNAs of hPIV-4B HN whose potential N-glycosylation sites wer e partially or completely the same as in hPIV-4A HN cDNA. We compared the a ntigenicity of the expressed wild-type and mutant proteins, and found that the antigenicities of the mutant hPIV-4B HN proteins were more similar to t he hPIV-4A HN protein than to the non-mutant hPIV-4B HN protein. This study indicated that the antigenic diversity between hPIV-4A and -4B was partly caused by deletion or creation of glycosylation sites, showing that the poi nt mutations resulting in deletion or creation of glycosylation sites is on e of the initial steps leading to the division of virus into subtypes.