Serological and cellular immune responses to non-structural proteins in animals infected with FMDV

In order to provide a rational base for the evaluation of FMDV non structural proteins as diagnostic probes, we have performed systematic longitudinal studies of the humoral and cellular immune responses to these proteins in animals infected with different FMDV serotypes. Although primary antibody responses to all the non structural proteins were observed, antibody titres were highly variable, ranging from insignificant in some cases, to clearly positive in others. In general, even the obvious positive responses were of short duration. For this reasons, discrimination between infected and vaccinated cattle is only possible at a herd level, and in our experiments the most useful target was the non structural protein 3A, although addition of 2C and 3C would provide a more sensitive test. As an alternative, with the major advantage of use directly on living cattle in the field, recombinant non structural proteins were evaluated in Delayed Type Hypersensitivity (DTH) skin tests. With this test, which measures Th1 type cellular immune responses, the most T cell immunogenic non structural proteins were 2B, 2C and 3D. Thus, DTH skin test could be a very useful tool to differentiate infected from vaccinated cattle.