Induction of IgE synthesis in anti-IgM-activated nonatopic human B cells by recombinant interleukin-3

The signals required to induce purified normal human B cell subpopulations into IgE production were studied. Pokeweed mitogen (PWM)-stimulated T cell supernatant induced IgE synthesis in low-density but not high-density Percoll-gradient-separated resting B cells. The PWM supernatant also enhanced (greater than 2-fold) IgE synthesis by anti-IgM (but not Staphylococcus A Cowan I)-activated high-density B cells (but not low-density B cells) and had affinity for lentil lectin. Subsequent studies were carried out using purified human recombinant interleukins (rIL). Human rIL-3 consistently (10/19 experiments) augmented IgE synthesis by anti-IgM-activated normal B cells. rIL-4 did not consistently (4/23 experiments) induce IgE synthesis by normal B cells or mixtures of T and B lymphocytes +/- monocytes. Furthermore, IL-1, IL-2, IL-5, IL-6, granulocyte, macrophage-colony stimulating factor (GM-CSF), granulocyte-colony stimulating factor (G-CSF), macrophage-colony stimulating factor (M-CSF) and interferon-gamma also failed to induce IgE synthesis. Identification of IL-3 as the factor(s) in the PWM supernatant that was responsible for inducing IgE synthesis was inconclusive since its effect could not be reversed by the addition of anti-IL-3 antibody. Thus, our results suggest that at least two distinct soluble factors are involved in the induction of IgE synthesis by nonatopic B cells.