Mucosal and systemic immune systems are quite separate in their proper
ties and in the factors which regulate them. In man, assessment of imm
une status at gut level, including the capacity to respond to oral vac
cines, should follow the general lines which are used in research and
clinical investigation of systemic immunity. All of the currently avai
lable methods for direct studies of gut immunity have limitations, but
a new technique, per-oral whole gut lavage with non-absorbable cleans
ing fluid, provides a system of gut perfusion. The value of this techn
ique is illustrated by data on intestinal antibodies to bacterial LPS
core antigens, of gut immunity in healthy African children, on the iso
type of antibodies elicited by oral killed whole cell/cholera toxin B
vaccine in coeliac disease patients, and on the effects of smoking on
intestinal antibodies elicited by the oral typhoid vacine Ty21a in hea
lthy UK adults. Finally, results of a recent comprehensive study show
that immunological tests using faeces are likely to be highly misleadi
ng.