AN ENZYME-LINKED-IMMUNOSORBENT-ASSAY SPECIFIC FOR TRANSIENT (29-37-KDA) FRAGMENTS OF SOLUBLE CD23 IGE-BINDING FACTORS/

The low-affinity IgE receptor (Fc(epsilon)RII) of B cells and monocyte s - also known as CD23 - is released from the cell surface by proteoly tic cleavage to yield a series of soluble fragments which can accumula te in cell culture supernatants and body fluids. Of these, the most st able is a 25-kDa molecule which is generated from transient intermedia tes ranging in size from 29 to 37 kDa. It has been claimed that these latter species act as IgE-promoting factors while the 25-kDa molecule is endowed with various cytokine-like activities which are independent of IgE binding. We describe here a novel enzyme-linked immunosorbent assay (ELISA) which allows for the distinction between these two class es of soluble CD23. It is based on the observation that the CD23 antib ody EBVCS1 can capture recombinant 29-kDa and 37-kDa fragments of CD23 but does not bind to the 25-kDa species: when EBVCS5 is used as the c apture antibody, all three fragments are bound. The availability of th ese differential ELISA should facilitate investigations on the biologi cal properties of CD23 fragments in health and disease.