Embryo vaccination of chickens with infectious bronchitis virus: histologic and ultrastructural lesion response and immunologic response to vaccination.

Chicken embryos 18 days of age and newly hatched chicks were vaccinated with an infectious bronchitis virus (IBV) vaccine (V-IBV) or with an IBV vaccine that had been serially passaged 40 times in chick kidney tissue culture (P-IBV). Immunologic and pathologic changes in the chicks were compared at selected intervals until the 35th day. Pathologic changes were evaluated by light, transmission, and scanning electron microscopy. Immunologic changes were assayed by a constant virus-diluting serum plaque-reduction test in chicken cell cultures, by 51Cr-release cytotoxicity assays, and by phytohemagglutination (PHA) responses. Embryos vaccinated with P-IBV and 1-day-old chicks vaccinated with V-IBV had similar transient lesions that were confined primarily to the trachea. Embryo vaccination and posthatch vaccination induced similar primary and secondary antibody responses in chicks. It was concluded that neither vaccination technique consistently influenced PHA response of whole blood cells or natural killer cell reactivity of spleen effector cells. Additionally, effector cells cytotoxic to IBV-infected target cells were not detected in chicks vaccinated as embryos or at hatch. The pathologic and immunologic effects of vaccination with P-IBV were comparable to those induced by conventional vaccination of chicks.