Although the various components of the two arms may differ, there
is accumulating evidence that both these host responses are in a
close and constant interaction and there is also evidence to suggest
that there is no distinct border between them, as originally thought.
Due to the lymphotrophic and highly cell-associated nature of MDV,
T cell-mediated immune responses are thought to play a more
important role compared to antibody-mediated responses. Since
the nature of MDV is cell-associated, antibodies play an important
role only when the virus is present in a cell-free form or when MDV
antigens are expressed on cell surfaces (Omar and Schat, 1996;
Sharma and Witter, 1975). Host responses to MDV infection within
various tissues, among MD resistant or susceptible birds, as well as
in response to vaccination have recently been reviewed by Parvizi