Comparison of mononuclear cell and B-lymphoblastoid histamine-releasing factor and their distinction from an IgE-binding factor

Abstract

We have characterized the histamine-releasing factors (HRF) from a B-lymphoblastoid cell line (RPMI 8866), compared it to mononuclear cell-derived HRF, and distinguished these from the IgE-binding factor produced by RPMI 8866. The B-cell-derived HRF fractionates at molecular weights of 90,000, 70,000, and 12–15,000 while mononuclear cell HRF has a major component at 24–26,000. The isoelectric points for B-cell HRF are 6.2–6.3 and 6.6–6.8 in contrast to 6.9 and 7.3 for mononuclear cell-derived HRF. The kinetics of histamine release by either HRF was the same, with half-maximal release in 5–10 min, unlike the rapid release caused by anti-IgE. Since HRF has been reported to be an IgE-binding factor, we screened column fractions for the IgE-binding factor secreted by RPMI 8866; this is known to be a shed low affinity IgE receptor. The chromatographic pattern and isoelectric point of this IgE-binding factor does not correspond to HRF; the purified IgE-binding factor had no significant histamine releasing activity on human basophils, and neither source of HRF was reactive in a radioimmunoassay to the IgE-binding factor. Our data suggest that HRF is quite heterogeneous and varies in physiochemical properties depending upon the cell source. The molecular relatedness (or nonrelatedness) of those HRFs is unclear; however, our data indicate that although HRF or fractions therefrom may bind to IgE as has been reported, it is unrelated to the low affinity IgE receptor.