Biliary Secretory IgA Levels in Rats with Protein-Calorie Malnutrition

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Abstract
Malnutrition is a recognized cause of failure of host defense mechanisms. In the past 5 years, it has been demonstrated that the gut, long known to have significant morphologic changes with protein calorie malnutrition (PCM), is an immune organ affected by malnutrition. To assess the role of biliary immunoglobulin A (S-IgA), part of the barrier to bacterial invasion from the gastrointestinal tract, the following study was performed. Seventy-eight Fisher female inbred rats weighing 110-130 g were randomly separated into two groups. The control rats were fed standard rat chow. The experimental rats were fed a 2% agar protein depletion (PCM) diet (USP XV). The biliary tract of the rat was cannulated with Silastic tubing and bile flow and rat secretory immunoglobulin A (S-IgA) was sampled at intervals. S-IgA was measured by the Elisa method. Total bile protein was measured by micro-Kjeldahl. Bile was collected from the rats on day 0, 7, 14, 21, 29, 36, 42, and 49. During the study, the weight of rats fed the PCM diet decreased from 127.4 +/- 14.5 g at day 0 to 83 +/- 2.6 g on day 37. Control rats gained weight from 124.4 +/- 14.5 g at day 0 to 153.6 +/- 3.8 g at day 37. Total biliary protein at day 0 was 2.52 +/- .05 mg/ml and at day 36 was 2.51 +/- 11 mg/ml for PCM rats and 2.57 +/- 10 mg/ml for control rats. Normal rats and control rats both had an initial increase of S-IgA from 2.74 +/- 73 mg/ml on day 0 to 5.75 +/- 1.75 mg/ml on day 37. Both PCM and control rats demonstrated an increase in S-IgA levels despite significant loss of weight in the experimental group. Similarly, total biliary protein was not decreased in either group. The results suggest that gut immune system is preserved despite significant protein calorie malnutrition.