Human recombinant interleukin 4 induces normal B cells to produce soluble CD23/IgE‐binding factor analogous to that spontaneously released by lymphoblastoid B cell lines

Abstract

Surface‐labeled Epstein‐Barr virus (EBV)‐transformed lymphoblastoid RPMI 8866 cells release in their supernatant a radiolabeled 25‐kDa polypeptide which reacts with the Fee RL/CD23‐specific monoclonal antibody (mAb) 25 and which binds to IgE but not IgG (IgEBF/sCD23). IgE BF/sCD23 had an isoelectric point of 4.5–5.0. The reactivity of mAb 25 with IgE BF/sCD23 allowed us to set up a radioimmunoassay for detection of IgE BF/sCD23 in cell culture supernatants. Supernatants from Fee RL/ CD23⁺ cell lines were found to contain IgEBF/sCD23. Addition of human recombinant interleukin 4 (IL4) to normal human B cells cultures induced the production of IgEBF/sCD23. Activation of B cells with anti‐IgM antibody coupled to beads enhanced the IL4‐induced production of IgEBF/sCD23 when compared to nonactivated B cells. This correlates with the finding that anti‐IgM antibody‐activated B cells cultured with IL4 express more FceRL/CD23 than B cells cultured with IL4 alone. The biochemical characteristics of radiolabeled IgE BF/sCD23 immunoprecipitated by mAb 25 from the supernatants of normal B cells cultured with IL 4 were identical to those of the IgEBF/sCD23 isolated from EBV‐transformed cell line supernatants. Addition of interferon‐γ to B cells cultured with IL 4 strongly decreased the level of IgE BF/sCD23 in culture supernatants correlating with the observed decrease of FceRL/CD23 on B cell surface. These data demonstrate that normal human B cells cultured in the presence of IL 4 produce an IgE‐binding factor (sCD23) biochemically and antigenically equivalent to that spontaneously produced by EBV‐transformed lymphoblastoid cell lines.