Local cholera immunity in mice: intestinal antitoxin-containing cells and their correlation with protective immunity

Methods for light and electron microscopic identification and characterization of intestinal cholera antitoxin-containing cells (ACC) using peroxidase-labeled immunoreagent are described and used to study the ACC response in mice after immunizations with cholera toxin. Specific ACC appeared in significant numbers after two oral immunizations and increased six- to eightfold with two additional oral boosters, whereas further oral immunizations caused no additional stimulation. Intravenous immunizations had to be repeated seven times before ACC could be detected. After two oral immunizations, most of the ACC were found in the proximal part of the small intestine and no ACC were seen in the colon. This uneven distribution of ACC within the small intestine was eliminated after four oral immunizations, when ACC could also be detected in the colon. The ACC response after four oral immunizations demonstrated a peak at 4 days with far fewer cells present at 2 and 7 days. Electron microscopic studies showed that the ACC were mature plasma cells with the staining localized to the endoplasmic reticulum. Regression analysis of the relationship between the number of ACC and the magnitude of protective immunity against intestinal challenge with cholera toxin indicates a highly significant correlation (r = 0.91, P less than 0.001).