A reappraisal of IgE levels in various human secretions by particle counting immunoassay combined with pepsin digestion.

We have assayed IgE in various human secretions by particle-counting immunoassay (PACIA). The introduction of a pepsin digestion step of the sample prior to the assay not only eliminates possible interfering factors but also releases from IgE the protease-resistant Fc"epsilon fragment. Since this fragment could represent the residual form of IgE in certain secretions rich in proteases it should be a suitable calibrator for the assay of IgE in secretions. The concentrations of IgE that we found in most fluids (urine, saliva, tears, milk, aqueous humour, cerebrospinal fluid, broncho-alveolar washings, intestinal fluids and faecal extracts) were up to 100 times lower than those reported by others who have used the radioimmunosorbent test (RIST). We suspect that the high values found with RIST are related to the susceptibility of this test to various interfering factors and not to a local production of IgE in most secretions of normal individuals.