Production of a chimeric form of CD23 that is oligomeric and blocks IgE binding to the Fc epsilon RI

The low affinity receptor for IgE (Fc epsilon RII/CD23) has previously been shown to interact with IgE with a dual affinity. Three chimeric constructs were created containing the lectin domain (amino acids 172-188) or the "ne ck" and lectin domain (amino acids 157-188) attached to subunits of oligome ric proteins. All chimeras were incapable of interacting with IgE with eith er a high or low affinity, indicating that the alpha-helical stalk of CD23 is important for orienting the lectin heads such that an interaction with I gE can occur. This concept received further support in that a chimeric CD23 composed of the human CD23 stalk and the mouse CD23 lectin head bound mous e IgE with a dual affinity, but could only bind rat IgE with a low affinity . Effort was next concentrated on a construct consisting of the entire extr acellular (EC)region of CD23, A mutation to the first cleavage site of CD23 (C1M) resulted in a more stable molecule as determined by a decrease of so luble CD23 release, A soluble chimeric EC-CIM was prepared by attaching an isoleucine zipper to the amino terminus (lzEC-C1M), The interaction with Ig E by lzEC-C1M was found to be superior to that seen with EC-CD23. The IzEC- C1M could inhibit binding of IgE to both CD23 and the high affinity recepto r for IgE, Fc epsilon RI, providing further evidence for a strong interacti on with IgE, Fc epsilon RT inhibition (similar to 70%) was seen at equimola r concentrations of IzEC-C1M, implying the effectiveness of this chimera an d suggesting its potential therapeutic value.