To explore the effect of nano aluminum oxide (A₂O₃) on neutrophil phagocytosis in mice exposed to different sizes of nano A₂O₃ particles, and to assess the impact on non-specific immune function in mice.

Threemonth-old healthy ICR male (n=20) and female (n=20) mice were randomly divided into five groups with four male mice and four female mice per group:blank control, solvent control (daily infusion of saline), 10 μm A₂O₃, 50 nm A₂O₃, and 13 nm A₂O₃ groups. Continuous exposure was conducted 3 times/d for 60 d by nasal drip and exposure dose was 50 mg/kg. Neutrophil phagocytosis was evaluated by oil immersion lens microscopy observation of 150 neutrophils on each Wright's stained blood smear which was prepared by mixing bacterial suspension and inner canthus blood sample of mice. Routine blood tests were also conducted.

The phagocytic percentages of the three A₂O₃ exposed groups were significantly lower than those of the blank control group and the solvent control group (all Ps<0.05). Compared with the 10 μm A₂O₃ group, the 50 nm A₂O₃ group had no obvious change in phagocytic percentage (P=0.06), but the 13 nm A₂O₃ group showed significantly lowered phagocytic percentage (P=0.01). Compared with the 50 nm A₂O₃ group, the 13 nm A₂O₃ had no obvious change in phagocytic percentage (P=0.08). The phagocytic indices of the three A₂O₃ exposed groups were lower than those of the blank control group and the solvent control group (all Ps<0.05). Compared with the 10 μm A₂O₃ group, the 50 nm A₂O₃ group and the 13 nm A₂O₃ group were significantly decreased in phagocytic index (both Ps<0.05). Compared with the 50 nm A₂O₃ group, the 13nm A₂O₃ group reported no significant change (P=0.85). Total white blood cells, lymphocyte counts, and lymphocyte percentages were higher in the 13 nm A₂O₃ group than in the blank control group and the solvent control group, and the differences were statistically significant (all Ps<0.05). No significant differences were found in the number of neutrophils (P>0.05).

Nano A₂O₃ could decrease neutrophil phagocytosis and influence the non-specific immune function in mice, and the phagocytosis would decrease with smaller sizes, indicating a potential size effect. Nano A₂O₃ could also cause an increase in the number of lymphocytes in peripheral blood.