Expression of interleukin-4 in apoptotic cells: Stimulation of the type-2 cytokine by different toxins in human peripheral blood mononuclear and tumor cells

Abstract

Background: Immunological reactivity is regulated by T-cell populations (type-1 and type-2 cells) via cytokine secretion, but their influence on apoptosis remains unclear. Methods: Intracellular expression of type-1 (interferon [IFN]-γ) and type-2 (interleukin [IL]-4) cytokines and apoptosis-related molecules (Apo2.7, Bcl-2 protein) was studied by flow cytometry in human peripheral blood mononuclear cells (PBMC), myeloma (U-266), monocytic (THP-1), and T-leukemia cells (MOLT-4) in response to toxins, which act on different intracellular targets (actinomycin D, cycloheximide, the mistletoe lectins [ML]-1 and ML-3, brefeldin A, staurosporine). Results: The apoptosis-inducing toxins stimulated intracellular IL-4 expression mainly in PBMC with high expression of the mitochondrial apoptosis marker, Apo2.7, but with decreased level of the anti-apoptotic Bcl-2 protein. Up-regulation of IL-4 coincided with a significant down-regulation of IFN-γ in CD4+ and CD8+ cells. The inhibitor of oxidative phosphorylation, oligomycin, and the caspase inhibitor, z-VAD-fmk, abolished IL-4 expression and DNA fragmentation in the PBMC. Also in the myeloma, monocytic, and T-leukemia cells, IL-4 was mainly observed in the Apo2.7+ apoptotic cells in response to the toxins. Conclusions: We suggest that the different apoptotic toxins activate a common pathway in which IL-4 production plays a yet unknown intracellular role further downstream during apoptosis. (C) 2000 Wiley-Liss, Inc.