Innate immune responses following emergency vaccination against foot-and-mouth disease virus in pigs

Inactivated "emergency" foot-and-mouth disease virus (FMDV) vaccine of high potency will induce early protection against the disease, implying a critical role for innate immune defences. At 3 and 6 days post-vaccination (dpv), there was no evidence of vaccine-induced specific anti-FMDV antibodies (Abs), nor enhanced uptake and destruction of opsonised virus by macrophages. Sera from vaccinates and control animals showed similar capacity to neutralise the virus, and were not different from the pre-vaccination sera. There were also no distinguishable changes in the distribution of the different peripheral blood leucocyte (PBL) subpopulations. Nor was any vaccine-induced increase in production of acute phase proteins noted. In contrast, chemotaxis assays identified an increase in PBL migratory activity which was vaccine-related. Furthermore, sera from 3 days post-vaccination contained elevated chemotactic potential. These results demonstrate that enhanced chemotaxis of cells of the innate immune defences, could play an important role during the early protection induced by emergency FMDV vaccines.