Differential cell counts in the BALF 1 and 21 day after NiNP exposure. Immune cells numbers for A) eosinophils, B) lymphocytes, C) neutrophils, and D) macrophages are presented as the mean values ± SEM out of a total of 500 cells counted per animal for 5–7 animals per dose group at 20× magnification. *p < 0.05, **p < 0.01, ***p < 0.001 compared to the time matched control group of the same genotype or as indicated. E) Photomicrographs representing each cell type. Macrophages and neutrophils demonstrated phagocytosis of NiNP in both genotypes at both time points in response to exposure (100×).