High intraluminal fluid flow increases intestinal IgA output

Stool IgA output in normal stool or chronic diarrhoea is a fraction of that recorded in high-output watery diarrhoea due to cholera. We hypothesized that high intestinal fluid flow leads to increased IgA output, and this is not a consequence of reduced degradation/reabsorption.

Daily intestinal outputs of IgA and other secretory and non-secretory proteins were measured in stool from 14 volunteers with ileostomies and compared with the output during whole-gut lavage, a whole-gut perfusion system.

Output into whole-gut lavage was significantly higher for all the proteins (P=0.02 to 0.001). Median IgA output into ileostomy effluent (IE) was 3.6 mg/kg/day compared with 26 mg/kg/day into whole-gut lavage fluid (WGLF). Thus IgA recovery in stool was only 12.7% of the amount in corresponding WGLF. Similar results were found for other proteins: specific IgA and IgM antibodies (5.4%-20.3%), IgM (42.4%), IgG (8.9%), and albumin (9.3%). Six subjects with IE water content >92% had increased recovery of IgA compared with eight with <92% water. In vitro, experiments predict that degradation of IgA within the small bowel results in 80% remaining compared with the 12.7% measured in vivo.

Our data show that high intraluminal fluid flow increases the intestinal output of IgA and other proteins, and this is not a consequence of reduced degradation/reabsorption in the colon or small bowel. This increased protein output may be a non-specific response in the early stages of acute diarrhoea.