SUMMARYThe spike (S), membrane (M) and nucleocapsid (N) proteins of avian infectious bronchitis virus strain M41 (IBV-M41) were separated by sucrose gradient sedimentation after dissociation of the virus by nonionic detergent. Groups of four chickens were inoculated intramuscularly with 20 ßg of S, M or N in Freund's complete adjuvant and at 4 and 7 weeks later with 20 ßg, of S, M or N protein in Freund's incomplete adjuvant. Chickens were bled at 4, 7, 10 and 13 weeks after the first vaccination and the sera analysed for serum virus neutralising (SN) and haemagglutination-inhibiting (HAI) antibody. Sera from all four chickens inoculated with S contained SN and HAI antibody. Maximum titres, in the range 5 to 9 logj, were attained after one, two or three injections in one, two and one chickens respectively. The SN and HAI titres rose in parallel. Neither M nor N induced detectable SN or HAI antibody. None of the chickens resisted challenge to the respiratory tract at 6 weeks after the final vaccination. Sera from chickens which had been infected twice with live IBV-M41 immunoprecipitated more radiolabelled S than N protein and little or no M. Similar results were obtained with sera from guinea pigs which had been inoculated intramuscularly with inactivated virus.
INTRODUCTION Avian infectious bronchitis virus (IBV), which causes infectious bronchitis in chickens, is a coronavirus comprising a lipid membrane, a single-stranded RNA genome and three protein structural elements: the nucleocapsid (N) protein, closely associated with the viral RNA, a heterogeneously glycosylated membrane (M) protein, which protrudes a little at the outer membrane surface, and tear-drop shaped surface projections or spikes (S) which protrude about 20 nm beyond the outer membrane surface (Davis and Macnaughton, 1979; for review see Siddell etal., 1983). The molecular weight of N is approximately 50 00C Daltons (50K), while that of the
