Marek's disease vaccines cause temporary U‐lymphocyte dysfunction and reduced resistance to infection in chicks

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Abstract
One‐day‐old chicks were vaccinated with one of the commercially used vaccines [herpes virus of turkeys (HVT), bivalent HVT+SB1 or Rispens] and the immune response and resistance to infection evaluated. A temporary depletion of B‐lymphocyte activity of varying intensity was found, as demonstrated by a diminished response to a B‐lymphocyte‐specific mitogen in vitro, and by decreased antibody production to BSA in vivo. Of the three vaccines tested, the bivalent vaccine (HVT+SB1) and Rispens were the most damaging. A temporary decreased resistance to pathogenic E coli infection in vaccinated chicks was observed.