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

Background: Immunological reactivity is regulated by T-cell populations (ty pe-1 and type-2 cells) via cytokine secretion, but their influence on apopt osis remains unclear. Methods: Intracellular expression of type-1 (interferon [IFN]-gamma) and ty pe-2 (interleukin [IL]-4) cytokines and apoptosis-related molecules (Apo2.7 , Bcl-2 protein) was studied by now cytometry in human peripheral blood mon onuclear cells (PBMC), myeloma (U-266), monocytic (THP-1), and T-leukemia c ells (MOLT-4) in response to toxins, which act on different intracellular t argets (actinomycin D, cycloheximide, the mistletoe lectins [ML]-1 and ML-3 , brefeldin A, staurosporine). Results: The apoptosis-inducing toxins stimulated intracellular IL-4 expres sion mainly in PBMC with high expression of the mitochondrial apoptosis mar ker, Apo2.7, but with decreased level of the anti-apoptotic Bcl-2 protein. Up-regulation of IL-4 coincided with a significant downregulation of IFN-ga mma in CD4(+) and CD8(+) cells. The inhibitor of oxidative phosphorylation, oligomycin, and the caspase inhibitor, z-VAD-fmk, abolished IL-4 expressio n 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 i n response to the toxins. Conclusions: We suggest that the different apoptotic toxins activate a comm on pathway in which IL-4 production plays a yet unknown intracellular role further down stream during apoptosis. Cytometry 41:261-270, 2000. (C) 2000 Wiley-Liss, Inc.