In vitro production of IgE-binding factors by human mononuclear cells

This study documents the production of IgE-binding factors (IgE-BFs) by unstimulated and by mitogen-activated human mononuclear cells. IgE-BFs were detected by a sensitive radioimmunoassay employing monoclonal antibodies to lymphocyte Fc epsilon R (MabER). IgE-BFs were found in the 24-hr CSN of unfractionated tonsillar lymphocytes and of their B-cell but not of their T-cell enriched fractions. When cultured for 1 week, PBMC spontaneously synthesized and released IgE-BFs in the CSN; this was significantly reduced by IgE (10 micrograms/ml). PWM, PHA and Con A significantly increased the production of IgE-BFs by PBMC, and this was not influenced by IgE. The production of IgE-BFs in response to mitogens required interactions between T and non-T cells, and IgE-BFs seemed to be derived mainly from non-T cells. However, low levels of IgE-BFs could be detected in the CSN of highly purified T cells cultured for 1 week in the presence of PHA. The production of IgE-BFs by non-T cells was T-cell dependent and it was mediated by soluble factors released from mitogen-activated T cells. T-cell factors increased the secretion of IgE-BFs by: the macrophage cell line U937, adherent cells, and adherent cell-depleted B-cell preparations. It is concluded that the majority of IgE-BFs produced by cultured human mononuclear cells are derived from B cells and monocytes, and that their production is regulated by T lymphocytes.