IgM turnover in Crohn's disease.

Simultaneous turnover studies with radioiodine-labelled IgM and IgG were made in 12 patients with Crohn's disease. Intestinal protein loss was estimated by means of (59)Fe-labelled iron dextran. The serum levels of IgM, IgG, and IgA were normal in most cases. The catabolic rate of IgM was increased in all but one case. A positive correlation was present between the catabolic rate and serum concentration of IgM, an observation which, so far, has been made only in Crohn's disease. The synthetic rate of IgM was raised or high normal in four cases with an intraabdominal abscess. It was normal in the remaining cases. A strong positive correlation was found between the synthetic rates of IgM and IgG. The size of the protein loss was unrelated to the raised catabolic rates of IgM and IgG.Faecal radioiodine excretion from labelled IgM and IgG bore no relation to faecal (59)Fe excretion, nor did it indicate the site of the intestinal lesion. However, a close correlation was observed between faecal excretion of the labels from IgM and IgG.