Quantification of antigen-specific antibody-secreting cells in the small intestine and other lymphoid organs of mice after oral booster immunization.

The intestinal immune response of mice against ovalbumin (OVA) was quantified by isolating lymphoid cells from the small intestine (SI) and testing them for antigen-specific immunoglobulin (Ig) secretion. The isolation procedure for functionally active lymphoid cells from the SI, originally developed to quantify the number of 'background' Ig-secreting cells in the SI, proved to be a useful method for evaluating antigen-specific intestinal immune responses quantitatively. The method was able to detect antigen-specific antibody-secreting cells (ASC) in the SI even when these cells occurred at a minimum frequency of only 0.006%. When mice were primed intraperitoneally (i.p.) with polymerized OVA and given an oral OVA booster immunization, OVA-specific ASC appeared in the SI from Day 3 after booster. After i.p. priming and an i.p. booster these cells could not be detected in the SI. The OVA-specific IgA-ASC responses in various organs after oral booster immunization were compared. From Day 5 after booster, when the response peaked, most OVA-specific IgA-ASC occurred in the SI. This suggested that these cells are mainly responsible for the OVA-specific antibodies demonstrated by ELISA in intestinal secretions from Day 6 after oral booster immunization. It is concluded that the quantitative method used in this study detects antigen-specific ASC in the SI with great sensitivity and could be used to evaluate immunization regimes aimed at inducing intestinal mucosal immune responses.