Fig 1. Particulate burden is measured by the percentage of macrophage cytoplasm taken up with particulate matter as calculated by digital image analysis of light microscopy images.

ImageSXM software analyses cytospin images treated with Fields B stain (A), and identifies both cytoplasmic (B) and particulate areas (C). The proportion of particulate to cytoplasm in the output image (D) is used as a measure of recent particulate exposure. Fifty 40x fields are used, and the overall mean particulate burden used as the summary statistic. Panels B and C are generated internally within the software, and are shown here for illustrative purposes only.