Bacterial agglutination studies with secretory IgA prepared from human gastrointestinal secretions and colostrum

The function of human purified colostral and gastrointestinal IgA has been studied by its ability to agglutinate common gastrointestinal organisms. Agglutinating activity was unaffected by trypsin or acid but it was abolished rapidly by pepsin. Both colostral and gastrointestinal IgA agglutinated a wide range of enteric organisms. Variations in this activity occurred between different individuals, and between different gastrointestinal sites in the same individual. In preliminary studies, saliva and IgA prepared from gastric and jejunal secretions in patients with pernicious anaemia showed a more uniform agglutination pattern than IgA prepared from the same sites in other patients. The agglutinin activity of IgA prepared from a particular site may be determined by the bacterial flora at that site. Agglutination methods for assessing the function of gastrointestinal antibody may be of value in the study of the possible roles of antibodies in inflammatory bowel disease.