Studies on the quantitation of immunoglobulin in human intestinal secretions

There is increasing evidence for the importance of the secretory immune system in the gut. In studies of local antibody production it is important to have satisfactory methods for measuring immunoglobulin concentrations and to be aware of the errors which may occur. Studies on immunoglobulin measurement in intestinal secretion by the radial immunodiffusion method are reported, showing the effects of proteolytic digestion, IgA molecular size, and sampling and storage conditions. Because of the presence of monomeric IgA in addition to secretory IgA, there is no satisfactory standard for IgA in gastrointestinal secretions, and only semi-quantitative results can be given. With radial immunodiffusion, IgG and IgM when subjected to tryptic digestion, and IgA when subjected to peptic digestion, may be overestimated because of the presence of fragments of immunoglobulins. In addition, pepsin rapidly destroys IgM and IgG. Both IgM and IgG are unstable in storage. The findings suggest that immunoglobulin concentration measurements in small intestinal aspirates should be interpreted with caution. These problems are also relevant to the detection of specific antibodies in gastrointestinal secretions.