Studies on human gastric mucosal immunoglobulin A. II. Further evidence for the absence of the secretory component from the predominant immunoglobulin A of human gastric mucus

Abstract

In this work fresh human gastric mucosal scrapings were fractionated on an isopycnic CsCl gradient into three fractions: L1, the top part of the gradient free of immunoglobulin A, immunoglobulin A-positive middle layer L2, and L3 the lower part of the gradient in which again immunoglobulin A was not detected, but which accounted for a large proportion of the total carbohydrate of the original suspension. Layer 2 (L2) was further fractionated by gel chromatography to give an immunogloblin A-enriched fraction S4B/2. The material in this fraction failed to reveal the presence of the secretory component indicating that the predominant gastric mucosal immunoglobulin A is not of the secretory type. In the second part of our work we have attempted to determine the effect of gastric mucosal scrapings on the secretory component of saliva as well as of milk whey. No apparent reduction of the amounts of the secretory component due to the presence of the scrapings was observed. We have also followed the fate of the immunological activity of the secretory component of the gastric-salivary immunoglobulin A-containing mixture throughout the whole fractionation scheme used for the isolation of the original gastric immunoglobulin A-positive fraction S4B/2. The secretory component was detected at all stages of fractionation of the mixture in the immunoglobulin A-containing fractions. These results indicate that, if present, the secretory component can be detected even in the presence of gastric mucosal components. Consequently, it is concluded that our inability to detect the secretory component in suspensions of gastric mucosal scrapings reflects the absence of this component from the tissue in measurable quantities, although appreciable quantities of immunoglobulin A are present.