Identification of paramyxovirus-specific haemolysis-inhibiting antibodies separate from haemagglutinating-inhibiting and neuraminidase-inhibiting antibodies. 1. Sendai virus haemolysis-inhibiting antibodies.

Egg-grown Sendai virus was used for preparation of rabbit hyperimmune sera directed against purified whole virus and pronasetreated projectionless virus particles. These sera and convalescent sera after natural Sendai infection in guinea pigs were studied in haemolysis-inhibition (HLI), haemagglutination-inhibition (HI) and neuraminidase-inhibition (NI) tests both before and after absorption with Tween 80-ether (TE) treated virus preparations. In addition, neutralization tests using the different sera were carried out. HI and NI antibodies and the major population of neutralizing antibodies in convalescent sera were removed by absorption with TE treated virus material without changing the titre of non-HI HLI antibodies. Rabbit hyperimmune sera directed against projectionless virus particles exhibited HLI antibody titres in marked excess of HI and NI antibody titres, whereas this was not found in sera against purified whole virus. In contrast, absorption of sera against projectionless particles eliminated HI antibodies without changing the titre of non-HI HLI antibodies. The protein composition of antigenic preparations used in absorption experiments and for preparation of sera was investigated by SDS-polyacryladmie-gel electrophoresis. TH treatment had no significant effect on the polypeptide pattern of Sendai virus. Pronase-treatment predominantly affected the two glycosylated proteins of Sendai virus. The larger glycoprotein was not detectable in pronasetreated projectionless virus particles, whereas the smaller glycoprotein was present in reduced quantities.