The gastrointestinal immune system is presented with a contrasting arr
ay of antigens, ranging from harmless dietary components to highly pat
hogenic microorganisms. The mucosal immune system has the ability to r
ecognise different groups of antigens and has evolved a battery of res
ponses from which an appropriate response may be orchestrated. The que
stion as to how the mucosal immune system categorises antigens and sel
ects a particular response is central to this process but it remains l
argely unanswered. The solution to this question is likely to hold the
key to the development of safe and effective mucosal vaccines as well
as suggesting methods for the prevention and control of allergic resp
onses. Enteric diseases resulting from antigens (microbial and dietary
) presented via the gastrointestinal tract are a major cause of morbid
ity and mortality. In addition to being of substantial economic import
ance, growing public awareness on animal welfare and food quality conf
irms the urgent need for new methods of disease control.