Eosinophil-active cytokine from mononuclear cells cultured with L-tryptophan products: an unexpected consequence of endotoxin contamination.

Abstract

The eosinophilia-myalgia syndrome, caused by a contaminant or contaminants in epidemiologically implicated L-tryptophan products, is characterized by eosinophilia and eosinophil degranulation. We hypothesized that immune cells are stimulated by implicated L-tryptophan and produce eosinophil-active cytokines. This study was designed to identify substances in L-tryptophan causing the eosinophilia-myalgia syndrome. Peripheral blood mononuclear cells were cultured with L-tryptophan products, and supernatants were tested for their ability to enhance eosinophil degranulation and survival in vitro and for their cytokine content. Subsequently, 46 different L-tryptophan lots were analyzed for their in vitro biologic activities. After peripheral blood mononuclear cells were cultured with implicated L-tryptophan, their supernatants enhanced eosinophil degranulation and survival. These activities were blocked by anti-granulocyte-macrophage colony-stimulating factor (GM-CSF) antibody; immunoreactive GM-CSF was measurable in the supernatants. Monocytes, but not T lymphocytes, were the responding cells. However, no correlation was observed between the in vitro biologic activity and lots of epidemiologically implicated L-tryptophan products. This biologic activity in the L-tryptophan products was characterized as endotoxin. Although L-tryptophan products stimulate peripheral blood mononuclear cells to produce GM-CSF, this response is caused by endotoxin contamination of the L-tryptophan products and not by a specific L-tryptophan contaminant. Endotoxin contamination must be considered as a possible cause of eosinophil-active cytokine production by peripheral blood mononuclear cells.