COMPARISON OF THE IN-SITU CHANGES IN LYMPHOID-CELLS DURING INFECTION WITH INFECTIOUS BURSAL DISEASE VIRUS IN CHICKENS OF DIFFERENT AGES

In situ immunocytochemical staining was used to characterise leukocyte changes and determine tropism of infectious bursal disease virus foll owing infection of neonate and 3-week-old chickens. In the bursae of b oth groups, massive replication of the virus, a rapid depletion of B c ells and an influx of CD4(+)TCR-alpha beta(1)(+) and CD8(+) TCR-alpha beta(1)(+) cells was detected within 4 days post-inoculation. Leukocyt e changes in the spleen, thymus and Harderian gland were similar in bo th groups. From 8 days post-inoculation onwards all the lymphoid organ s became repopulated with leukocytes and tissue architecture began to be slowly restored. Virus neutralizing antibodies developed more slowl y in neonate birds and at 21 days post-inoculation the titres were muc h lower compared to older birds. Lack of clinical signs in neonate chi ckens was neither due to a failure to respond to the virus, to recruit leukocytes to the infected tissues nor to a lack of viral replication .