Table 1. Description of IBV strains used in this study.

Strain	Genotype	Designation	Strain information	Refs
H120	Massachusetts	Vaccine	Nobilis IB H120 vaccine strain produced by serial egg passage - not pathogenic in infected birds	49
Beau-R	Massachusetts	Apathogenic lab	Molecular clone of IBV-Beaudette-CK, which was attenuated by serial egg and CK cell passage - not pathogenic in infected birds	20,50
M41	Massachusetts	Pathogenic lab	Adapted for growth in CK cells by serial passage - severe respiratory symptoms in infected birds	19,47
D1466	D212	Pathogenic field	First isolated in Holland in 1960s - early isolates minimally pathogenic, but recent isolates like this one cause cystic ovaries and nephritis	51,52
4/91	4/91	Pathogenic field	First isolated in UK in 1991 - respiratory symptoms and nephritis	53, 54, 55
Italy02	Italy02	Pathogenic field	First isolated in Italy in 2002 - respiratory symptoms and nephritis in young birds, egg drop in adult birds	56,57