Changes in the harderian gland of the chicken following conjunctival and intranasal infection with infectious bronchitis virus in one‐ and 20‐day‐old chickens

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Abstract
Three days after conjunctival and intranasal infection with IB vaccine virus a great increase in the number of plasma cells together with an increase in vascularization was observed in the stroma of the Harderian gland of chickens vaccinated either at one day of age or 20 days old. From 7 days to 21 days after vaccination a pronounced formation of follicles occurred which were composed of lymphocytes. Birds exposed to diluted allantoic fluid showed a limited increase of plasma cells only; follicle formation was not observed. The changes in the gland were the same in chickens vaccinated at one day of age which had high levels of circulating antibody as in chickens vaccinated at 20 days of age which had low levels of antibody to IB virus. Conjunctival and intranasal challenge with a virulent field IB virus 28 days after vaccination resulted in severe hyperaemia of the follicles and slight degeneration of lymphocytes and plasma cells. This was in contrast to the severe hyperaemia and massive degeneration of plasma cells 3 and 7 days after challenge of unvaccinated birds of the same age with virulent field IB virus. In these birds no follicle formation was seen 14 days after challenge which was in contrast with the follicle formation 14 days after infection with the vaccine virus. Re‐exposure to the non‐infective allantoic fluid resulted in a slight increase in the number of plasma cells only.