Structural proteins of avian infectious bronchitis virus: role in immunity and protection

The antigenicity of the S1, M and N proteins of avian infectious bronchitis virus was compared following immunization of chickens with live and inactivated virus. The N protein was immunodominant antigen inducing cross-reactive antibodies in high titres whereas the S1 glycoprotein induced serotype-specific and cross-reactive antibodies. The M glycoprotein elicited antibodies in low titres and of limited cross-reactivity. Immunization of chickens with the purified N and M proteins did not induce protection against virulent challenge whereas immunization with the S1 glycoprotein prevented replication of nephropathogenic IBV in kidneys but not in tracheas of immunized chickens.