Newcastle disease virus vaccines: differences between Line C and Line 15I chickens with respect to virus replication and IgA responses in the gut and Harderian gland.

The Ulster 2C and Hitchner B1 strains of Newcastle disease virus were inoculated into inbred White Leghorn birds of the Reaseheath-C and 15I lines by the oculonasal route. Both viruses replicated in the Harderian gland (HG) and induced virus-specific IgA in the tears and bile. Ulster 2C but not Hitchner B1 replicated in the small intestine and induced virus-specific antibody forming cells (AFC) in the small intestine. Line 15I birds produced 120-fold more virus and 13-fold more IgA-AFC in the small intestine than Line C birds. Line C birds produced 20-fold more virus in the HG and at least three-fold higher titres of lacrimal IgA than Line 15I birds. The level of local virus replication in the HG or small intestine, which varied according to the line of bird, positively predicted the local antibody response in the same organ. When low doses of Ulster 2C were inoculated into Line C birds virus replication was low and irregular in birds older than 18 days whereas low doses of Hitchner B1 replicated in all ages of bird.