Protection from IBDV-induced bursal damage by a recombinant fowlpox vaccine, fpIBD1, is dependent on the titre of challenge virus and chicken genotype

Expression of the VP2 capsid protein of infectious bursal disease virus (IB DV) in an vaccine strain of fowlpox has produced an experimental recombinan t vaccine, fpIBD1. Successful vaccination with fpIBD1 was dependent on the titre of challenge virus for high titres of challenge virus were able to ov ercome protection induced by fpIBD1 whereas challenge with a low titre of v irus did not. The genotype of chicken also has an important effect on the o utcome of challenge possibly as a result of the major histocompatability co mplex and its ability to present VP2-derived peptides to the immune system. It was not possible to protect the inbred white leghorn chicken strain, li ne 15I, from IBDV-induced bursal damage by vaccination with fpIBD1 even at the lowest titre of challenge virus used. All other inbred white leghorn ch ickens examined (line 6(I), C.B4 and C.B12) and outbred Rhode Island Red ch ickens were protected by fpIBD1. Protection by the fpIBD1 vaccine is induce d in the absence of detectable serum antibodies, suggesting the possibility of a significant role for cell-mediated immunity in protection from IBDV c hallenge. (C) 2000 Elsevier Science Ltd. All rights reserved.