[Immunization effect on Naegleria fowleri infection in splenectomized mice]

A pathogenic free-living amoeba, Naegleria fowleri, is a causative protozoan parasite of primary amebic meningoencephalitis in human and experimental animals. It is known that humoral and cellular immunity contribute as the defence mechanism of host against this organism. Recently splenectomy has been argued on its effect on host defence mechanisms. The present study was aimed to observe the effect of immunization in splenectomized mice. For immunization, 5-10 x 10(5) trophozoites of Naegleria fowleri o 359 were intraperitoneally inoculated once a week for two weeks to BALB/c mice, and 5-10 x 10(4) of ameba trophozoites were intranasally inoculated for infection after splenectomy and/or immunization. ELISA technique was applied for the detection of serum IgG antibody levels. Experimental animals were divided into 4 groups; I. splenectomized and immunized; II. splenectomized only; III. immunized only; IV. not splenectomized nor immunized. The results obtained were as follows: Mortality rates of splenectomized and immunized mice in group I (38.1 percent) and immurized only in group III (25.0 percent) were lower than those of not immunized mice in group II(50 percent) and control group, IV (46.4 percent). Survival times of mice in group I, II, III and IV were 20.1+/-3.6, l7.3+/-4.5, 20.4+/-7.0 and 19. 6+/-7.6 days respectively, and there were no significant differences between them. ELISA values (absorbance at 492 nm) of group I (1.10+/-0.29) and group III (1.31+/-0.28) were signficantly higher than that of group IV(0.24+/-0.37) at day 31 of infection (p<0.05). Conclusively, it is presumed that humoral immunity against N. flowleri may operate as ever, after immunization, even though the mouse was splenectomized.