Effect of recombinant human interleukin 4 on spontaneous in vitro human IgE synthesis

Recombinant human interleukin 4 (IL 4) alone enhanced the spontaneous IgE synthesis in cultures of peripheral blood leukocytes (PBL) from atopic patients as well as from nonatopic individuals, suggesting the existence of preactivated PBL sensitive for IL 4. Preactivated cells were also obtained by stimulation with Staphylococcus aureus strain Cowan I (SAC). However, co-stimulation of PBL by IL 4 with SAC or anti-IgM antibody and pokeweed mitogen did not result in an enhanced IgE synthesis. Optimal IL 4 concentrations for the induction of IgE synthesis coincided with optimal proliferative responses in PBL. The effect of IL 4 was not isotype specific, and in terms of protein even more IgG and IgM antibodies were formed. The effect of IL 4 on IgE synthesis was counteracted by very low concentrations of interferon-gamma (IFN-gamma), suggesting that both IL 4 and IFN-gamma might be decisive cytokines for the human in vitro IgE synthesis.