[The effect of silica on the development of experimental Acanthamoeba meningoencephalitis with reference to the macrophage role in mice].

The role of macrophages was observed in intranasally infected C3H/HeJ mice with trophozoites (3 x 10(5)) of Acanthamoeba culbertsoni which was a kind of free-living amoebae inducing meningoencephalitis in human and experimental animals. The mortality was 60% in the group of intraperitoneally injected mice with silica (0.5 mg/0.5 ml). It was much higher than that of 10% in the group of amoeba infected mice without silica administration. The phagocytic index of peritoneal macrophages co-cultured with Toxoplasma gondii was estimated daily. In contrast to the control and amoeba infected group which didn't show significant fluctuation of the phagocytic indices, the silica administrated group revealed under 3% until day 3, and gradual increase up to 24.7% in day 5 which was same level of amoeba infected group without silica administration. The level of interleukin-1b (IL-1b) measured by ELISA was the highest in the amoeba infected group without silica injection and the lowest in the amoeba infected group with silica administration. In the test of the amoebicidal activity of mice peritoneal macrophages in vitro, silica administration revealed reducing effect on amoebicidal activity of macrophages. In conclusion, macrophages were proven to play a significant role in defense mechanism against the development of experimentally induced Acanthamoeba meningoencephalitis.