The concentrations of endotoxins in the collected samples presented together with PM-induced IL-6 from alveolar rat macrophages after exposure to 20 μg/ml of coarse (C) and fine (F) fractions collected in Oslo, Rome, Lodz and Amsterdam in spring (upper), summer (middle) and winter (lower) seasons. IL-6 release is shown on the left ordinate, values in diagram are mean ± SEM (n = 3). Concentration of endotoxin is shown on the right ordinate (ng/mg PM). Endotoxin content in PM samples measured by the LAL-method and the EPT-method are shown. LAL-analysis of the Oslo spring samples is missing due to shortage of sample material.