Table 3. Priming of tracheal protection by primary immunization of chickens with IBV N protein (modified from Boots et al., 1992).

	Number of protected chickens
	Ciliary activity assay		Immunofluorescence assay
Primary immunization	Challenge after primary immunizationa	Challenge after secondary immunizationb	Challenge after primary immunizationa	Challenge after secondary immunizationb
Inactivated IBV	1/8	8/8	NDc	7/8
β-galactosidase–IBV N protein	0/8	8/10	ND	7/10
fusion protein
β-galactosidase	0/8	8/12	ND	4/12

^aChickens were challenged by eye-drop 4 weeks after primary immunization.

^bThe secondary immunization was inactivated IBV. Chickens were challenged by eye-drop 4 weeks after secondary immunization.

^cND, not done.