Effect of L-Tryptophan Products on Function of Human Eosinophils: Investigation of the Causal Mechanisms of Eosinophilia Myalgia Syndrome Associated with L-Tryptophan Products

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Abstract
Contaminants in the L-tryptophan products, known as peak-E and peak-5, at a concentration of 1–10 μg/ml had the ability to elicit chemokinetic migration of eosinophils. Purified eosinophils adhered to peak-E- or peak-5-stimulated human umbilical vein endothelial cells, and this adherence was inhibited by the presence of antibody to intercellular adhesion molecule-1 but not by vascular cell adhesion molecule-1 antibody. Neither contaminant affected the expression of integrins, e.g. CDllb or CD49d, on the purified eosinophils. Human peripheral blood mononuclear cells (PBMCs) produced eosinophil survival-enhancing activity when cultivated with peak-E, but not with medium alone, peak-5 or control tryptophan. This activity of peak-E was significantly inhibited (p < 0.01) by the presence of antibody to granulocyte-macrophage colony-stimulating factor (GM-CSF). In addition, expression of GM-CSF mRNA was found in total cellular RNA isolated from peak-E-stimulated PBMCs. Eosinophils acquired the ability to migrate toward interleukin-8 (IL-8) when preincubated with the contaminants of interest. IL-8 also bound to the contaminant-stimulated eosinophils, but not to those stimulated with medium alone. These findings suggest that contaminants in the L-tryptophan products modify the several functions of eosinophils and play a role in the pathogenesis of eosinophil myalgia syndrome.

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