Infected and apoptotic cells in the IBDV-infected bursa of Fabricius, studied by double-labelling techniques

Infections of young chickens with infectious bursal disease virus (IBDV) re sult in depletion of lymphoid cells of the bursa of Fabricius (BF) due to n ecrosis and apoptotic processes. Interactions between IBDV and lymphoid cel ls were investigated by labelling paraffin-embedded tissue sections of infe cted BF with combinations of either immunohistochemistry (IHC), in situ hyb ridization (ISH) or in situ TUNEL reaction (IST), With regard to specificit y and sensitivity, results of ISH were comparable to those of IHC, By doubl e-labelling it was shown, for the first time, that viral antigen was presen t in most of the apoptotic cells, This suggests that IBDV may be directly i nvolved in the induction of the apoptotic process. However, some cells also showed either viral antigen or DNA fragmentation, especially at the early stages of infection. It should be taken into account, therefore, that the a poptotic processes might also be induced by IBDV through indirect interacti on between cells. Remarkably, in some of the infected lymphoid cells ISH si gnals were observed in the nucleolus.