Human mononuclear cell-derived histamine-releasing factor (MNC-HRF) has m.w. of 29,000 and 23,000 and two charge species isoelectric at pH 6.9 and 7.3. Minor forms of HRF are also seen at m.w. of 12,000 to 15,000 and 60,000 to 80,000. In this manuscript we have further defined the response of human basophils to MNC-HRF in terms of atopic status of cell donors and the role of IgE antibody. We found that basophils of allergic persons, nonallergic controls, or donors who have positive skin tests but no symptoms, cannot be distinguished based upon responsiveness to HRF. Further, the response of basophils that have been desensitized to anti-IgE is retained when they are subsequently stimulated with HRF derived from human MNC. Thus an interaction with cell-surface IgE to cause histamine release is not evident. Nevertheless, one of two IgE myeloma proteins tested were capable of binding HRF and such binding could be utilized as a purification step. We conclude that MNC-HRF is heterogeneous in terms of size, charge, and affinity for a subpopulation of IgE. Histamine release is more prominent in atopic individuals but does not appear to require an interaction with IgE.

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