Functional restoration of the bursa of Fabricius following in ovo infectious bursal disease vaccination

The primary role of the avian bursa of Fabricius is to provide an essential microenvironment for B-lymphocytes to diversify their immunoglobulin genes by gene hyperconversion. Infectious bursal disease (IBD) vaccination using intermediate plus vaccine strains can temporarily deplete the bursal folli cles and interrupt the normal B-cell development, which is generally follow ed by B-cell repopulation and histological regeneration. To find evidence t hat functional restoration of the bursa of Fabricius occurs in addition to the histological regeneration, we have analysed the chB1 gene expression, w hich indicates active bursal B-lymphocytes, and also the surface expression of a carbohydrate structure Lewis(x), a marker which identifies those burs al B-lymphocytes that are undergoing gene hyperconversion. In ovo vaccinati on with an immune complex vaccine (IBDV-BDA) caused transient bursal destru ction in both the SPF and the maternally protected broiler groups with diff erences evident in the starting time, the severity and the duration of the effect. After the depletion phase, signs of histological regeneration appea red together with chB1- and Lewis(x) expression indicating that B-lymphocyt es were functionally active and the bursa of Fabricius was serving again as an efficient primary lymphoid organ providing an appropriate microenvironm ent for B-cell development. (C) 2001 Elsevier Science B.V. All rights reser ved.