IgG and Albumin Turnover in Crohn's Disease

Simultaneous IgG and albumin turnover studies were performed in 10 patients with Crohn's disease of the terminal ileum, the colon, or both, by means of radioiodinated proteins. An abnormal intestinal protein loss was demonstrated in everyone with 59Fe-labelled iron dextran. The serum level of IgG was normal in 5 and elevated in 3 cases. The higher the serum level, the higher was the fractional catabolic rate (per cent of intravascular mass catabolized per day). The synthetic rate was markedly increased in most cases. In contrast, serum albumin was negatively correlated to its catabolic rate. Albumin synthesis was normal or moderately elevated. The regression between the catabolic rates of IgG and albumin in 7 cases of intestinal lymphangiectasia and in 10 cases of Crohn's disease suggested that, in intestinal lymphangiectasia, the protein loss of albumin was higher than that of IgG, whereas, in Crohn's disease, the IgG catabolism for unknown reasons was higher than that of albumin. All patients with Crohn's disease had normal serum levels of IgA and IgM. The leucocyte migration test with small intestine or colon mucosa as antigens was normal in all cases of Crohn's disease. This is in contrast to the findings in ulcerative colitis where a cellular hypersensitivity to these antigens has been demonstrated. It is concluded that the ability to develop humoral hypersensitivity is probably normal in Crohn's disease. An abnormally high fraction of the total mass of both IgG and albumin was present intravascularly in most patients. Faecal radioiodine excretion from labelled IgG and albumin was high in patients with colonic involvement. In patients with terminal ileitis the faecal excretion of the IgG-label was higher than that of the albumin-label.