Technical Report: results of immunological tests on faecal extracts are likely to be extremely misleading

Abstract

SUMMARYClinical investigation of gut immunity is difficult because of the need to study intestinal tissues or secretions directly. Others have reported that immunoglobulins, antibodies and cytokines can be detected in saline extracts of faeces. We have assessed the validity of this approach by measuring immunoglobulins, albumin, a|-antitrypsin and isotype-specific antibodies in matched samples of faeces and whole gut lavage fluid. Results were compared as estimated output per day, and by using haemoglobin as a common reference substance. Samples were obtained from 10 patients with active infiammatory bowel disease and 10 with other benign Gl diseases. For immunoglobulins, albumin and antibodies, the amount detected in faeces varied from < 0 01% to 355% (based on estimated daily output) and < 0 01 % to 18 5% (based on haemoglobin) of the amount known to be produced in the gut from results of assays on whole gut lavage fluid (WGLF); there were significantly higher rates of recovery in faecal specimens from patients with active gut inflammation than from other patients. Detection rates and titres of specific antibody in faeces were even lower than those for immunoreactive IgA. These data indicate that immunological tests on saline extracts of faeces do not represent the true status of the gut humoral immune system, and such studies should be strongly discouraged.

Purification and functional characterization of mucosal IgA from vaccinated and SIV-infected rhesus macaques

“…Up to 70 times more IgA can be purified from feces compared to secretions collected by rectal swabs. The use of fecal extracts for monitoring mucosal IgA in the gastrointestinal tract has been criticized as unrepresentative of amounts present in whole gut lavages [52]. However, this previous study did not purify IgA.…”

Collection and Processing of External Secretions and Tissues of Mouse Origin

“…Methods for obtaining this type of sample from mice include intestinal lavage (Elson et al, 1984;Grewal et al, 2000;O'Mahony et al, 1990), extraction of fecal samples (deVos and Dick, 1991;Grewal et al, 2000), or sampling with Polyfiltronics wicks (Haneberg et al, 1994). Fecal extracts have been used as a substitute for the laborious lavages and directly sampled intestinal specimens but the validity of this approach has been questioned (Ferguson et al, 1995). However, when samples obtained by these techniques were compared for contamination with Igs derived from the blood circulation ( Meckelein et al, 2003), the lowest levels of plasma-derived IgA were found in feces, followed by intestinal lavages, and the highest levels were in filter wick-collected samples.…”

Collection and Processing of Human Mucosal Secretions

“…In some studies, fecal extracts have been used for measurement of intestinal antibodies. However, the use of such specimens should be discouraged because of the precipitous decline of immunoglobulins because of their rapid digestion by fecal proteases and the limited information obtainable (Ferguson et al, 1995).…”