SERUM LEVELS OF IGE-BINDING FACTOR (SOLUBLE CD23) IN DISEASES ASSOCIATED WITH ELEVATED IGE

Several in‐vitro experiments suggest that the low affinity receptor for IgE (FcɛR II) and its soluble fragment (IgE‐binding factor, IgE‐BF) are multi‐functional molecules and more particularly that they are capable of regulating the synthesis of human IgE. I nan attempt to examine the in‐vivo significance of these in‐vitro observations, the serum level of IgE‐BF was measured in individuals with allergic or parasitic diseases, both associated with an increased production of IgE. IgE‐BF was measured by a radioimmunoassay employing two mAbs against FcɛRII (mAbER). We first compared 257 allergic subjects to 172 non‐allergic controls matched for age and sex. Statistical analysis of the data, after logarithmic transformation of IgE‐BF and IgF. values, revealed that despite a great overlap, the allergic subjects had significantly higher levels of IgE‐BF. The correlation between IgE and IgE‐BF was very weak but significant. Allergic or non‐allergic children had significantly higher IgE‐BF levels than the corresponding groups of adults; moreover, the in verse correlation between age and IgE‐BF levels was significant only in the children and not in the adults. The IgE‐BF levels were not influenced by gender, by hyposensitization therapy or by treatment with local steroids. Subjects receiving systemic steroids had lower IgE‐BF levels than untreated subjects. To assess the effect of seasonal exposure to allergen, IgE‐BF levels were monitored for 1 year in six rye grass‐sensitive hay fever subjects known to display a seasonal increase of both total serum IgE and of specific anti‐Lol p I and Lol p II IgE antibodies. The levels oflgE‐BF remained stable in the hay fever subjects as well as i n the non‐allergic controls. Twenty subjects with filariasis and high serum IgE concentrations also displayed increased levels of serum IgE‐BF when compared to control individuals. The serum IgE‐BF detected by the RIA was not bound to IgE as shown by two independent observations: (1) they were not adsorbed on an anti‐IgE immunoadsorbent column and no serum IgE was retained on an immunoadsorbent column coupled to mAb against IgE‐BF; and (2) the serum molecules binding to mAbER‐coated solid phase did not react with radiolabelled monoclonal or polyclonal anti‐IgE, and reciprocally the serum molecules binding to anti‐IgE‐coated solid phase did not react with labelled mAbER. Taken collectively, the present data are compatible with, but do not add further support to, the hypothesis that IgE‐BF may regulate the synthesis of human IgE. Copyright © 1990, Wiley Blackwell. All rights reserved