Immunoglobulin E (IgE) was demonstrated by a double antibody radioimmunoassay technique (PRIST) in 5 of 17 unconcentrated fecal extracts from children. Four of the PRIST-positive extracts also had measurable levels of IgE determined by an enzyme-linked immunosorbent test (Enzygnost IgE). However, using a competitive antibody radioimmunoassay technique (RIST), IgE was found in all unconcentrated fecal extracts. The RIST-IgE levels of the extracts were higher and did not correlate to IgE measured by the other methods, nor to the IgE in serum from the same children or to the manifestation of allergy. On the other hand, 4 of the 5 children with measurable PRIST-IgE levels, and 3 of the 4 children with detectable Enzygnost IgE concentrations in the extracts, had elevated serum IgE as well as a history of allergy. Gel filtration studies indicated that IgE determined by the PRIST and Enzygnost IgE methods had been degraded to fragments of lower molecular weight than that of albumin. This study also suggests that the IgE in feces measured by the RIST method is overestimated due to the influence from nonspecific substances of high molecular weight.
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