MEASURING THE CELLULAR RESPONSE OF MACROPHAGES TO SOIL COMPONENTS BY FLOW CYTOMETRY: DETERMINING THE TOXICITY OF PODOCONIOSIS-ASSOCIATED SOILS

Certain minerals are known to be harmful to human cells. Silica and asbestos affect the lungs and can cause cancer. A lesser–known disease called podoconiosis affects a large population in Ethiopia. Podoconiosis is characterized by lymphedema of the feet and legs. It has been suggested that silica particles in soils may enter the lymphatic system through the feet causing immune–related obstruction. Although silica has been suggested, no specific mineral or mineral properties have been confirmed and no rationale for why such a common mineral should be so virulent in these particular locations. Research has also suggested a genetic component to the disease.

Our investigation employed two approaches. The first arm focused on comparing soil mineralogy, texture and composition from podoconiosis­–associated regions to unaffected regions. The high clay content of soils in diseased regions has often been referenced as its small size would allow it to easily enter the lymphatic system. Particle size data confirms higher concentrations of clay–sized particles in podoconiosis–associated soils compared to unassociated soils, which are dominated by kaolinite, smectite and mixed layer clays. Geochemical analyses of the fine fraction shows higher concentrations of several transition metals in podoconiosis-associated soils than in unassociated soils. XRD analysis of fine sand and silt fraction found higher proportions of some feldspars, pyroxenes, amphiboles, feldspars and oxides in podoconiosis-associated soils.

The second arm focused on developing flow cytometry to quantify the immune response of macrophage cells to various minerals and soil particles. Our protocol confirmed previous reports that silica (5 mm) is toxic to macrophages (MH-S; CRL­2019) after 24 hours of exposure with an LD50 of ~ 2 particles/cell, while latex beads (4.5 mm) showed little effect on the cells even at high doses (33 particles/cell). Podoconiosis–associated soils show a toxicity that appears similar to silica. Using weight/volume (mg/mL) rather than particles/cell, the toxicity (LD50) for podoconiosis–associated and unassociated soils are being compared to silica, kaolinite and latex beads to determine the relative soil toxicity. Further flow studies are planned to evaluate macrophage activation and fibrogenic ligand production.