Measurement of specific IgA in faecal extracts and intestinal lavage fluid for monitoring of mucosal immune responses.

Currently available methods for the evaluation of antigen-specific immune responses in the intestine, i.e. measurement of IgA in intestinal lavage and antibody secreting cells (ASC) in peripheral blood, are not applicable to large-scale immunogenicity studies or to kinetic studies where repeated sampling is required. Simple and reliable methods need to be developed. Intestinal lavage and faecal samples were collected from 12 mice on days 0, 14, 21, 28 and 35 following initial immunization with four doses of cholera toxin (CT) by the gastric or rectal routes. The concentrations of anti-CT IgA in the faecal extracts showed a high level of correlation with those in the lavage samples (Spearman's correlation coefficient=0.85, P<0. 0001) regardless of the route of CT administration. Moreover, the kinetics of the immune response as reflected in the faecal extracts mirrored those in the lavage samples regardless of immunization route. As compared to gastric immunization, rectal administration of CT yielded higher levels of anti-CT IgA in both intestinal lavage fluids and in faecal extracts. The use of rectal immunization and the measurement of IgA in faecal extracts for monitoring mucosal immune responses may be relevant for the development of effective enteric vaccines.