URBAN PARTICLE-INDUCED APOPTOSIS AND PHENOTYPE SHIFTS IN HUMAN ALVEOLAR MACROPHAGES

Epidemiological studies report a small but positive association betwee n short-term increases in airborne particulate matter and small increa ses in morbidity and mortality from respiratory and cardiovascular dis ease in urban areas. However, the lack of a mechanistic explanation to link particle exposure and human health effects makes it difficult to validate the human health effects. The present study tested the hypot hesis that urban particles could cause apoptosis of human alveolar mac rophages (AM) and a shift of their phenotypes to a higher immune activ e state, which would provide a mechanism to explain an inflammatory re sponse. Freshly isolated human AM were incubated for 24 hr with urban particles (#1648 and #1649), Mount Saint Helen's ash (MSH), and residu al oil fly ash (ROFA). Cell viability was assessed by trypan blue excl usion and apoptosis was demonstrated by morphology, cell death ELISA, and DNA ladder formation. Additionally, AM were characterized accordin g to RFD1(+) (immune stimulatory macrophages) and RFD1(+)7(+) (suppres sor macrophages) phenotypes by flow cytometry. ROFA particles caused A M necrosis at concentrations as low as 10 mu g/ml, urban particles had no effect except at 200 mu g/ml, and MSH had no effect at 200 mu g/ml . ROFA (25 mu g/ml) and particles #1648 or #1649 (100 mu g/ml) caused apoptosis of AM by all three criteria, bur 200 mu g/ml MSH had no effe ct. Finally, 25 mu g/ml ROFA and 100 mu g/ml particles #1648 or #1649 up regulated the expression of the RFD1(+) PLM phenotype, while only R OFA decreased the RFD1(+)7(+) phenotype. Consequently, ROFA and urban particles can induce apoptosis of human AM and increase the ratio of A M phenotypes toward a higher immune active stare (i.e., increased RFD1 (+):RFD1(+)7(+) ratio). If urban particles cause similar changes in vi vo, this could result in lung inflammation and possible increased pulm onary and cardiovascular disease.