Isocyanate-albumin is taken-up and accumulates in cells of monocyte lineage. PBMCs were cultured with fluorescently labeled control “mock exposed” albumin (albFITC) or HDI-albFITC, and analyzed under phase contrast (left frame) and fluorescence (right frame) microscopy at different time points shown (panel A). HDI-albFITC, but not albFITC is taken-up along the outer cell membrane in a subset of cells, and accumulates over time. Monocyte-derived cells (panel B), but not T cells (panel C) are the major cell type that take up HDI-albFITC (green), as shown by dual staining with PE (red)-labeled α-CD14 or α-CD3, at 2hr and 3 day time points respectively.