Present study aimed to elucidate the immunosuppressive effect of prednisolone on Naegleria fowleri infection in mice. N. fowleri was cultured in CGVS medium (Willert and Le Ray, 1973). White female mice, weighing about 18 g, used for experiments were divided into five groups; untreated control group, prednisolone treated groups (before, during and after infection), and only prednisolone treated group. In the prednisolone treated group, the hormone was injected intramuscularly 5 doses of 10 mg/kg every other day. According to designated time of treatment, each mouse was challenged with 1 x 10(5) N. fowleri intranasally. Changes of body weights, clinical manifestations and number of dead mouse were observed. Brain and lung tissues of dead mice were cultured in the non-nutrient agar (Kasprzak and Mazur, 1972), or stained with hematoxylin-eosin for the examination of histopathological changes. Results of the experiment are summarized as follows: Mortality among the prednisolone treated groups was higher than that in untreated control group, and among the treated groups, the pretreated group showed shorter survival time. Body weights among untreated control mice showed no significant increase, however, treated groups of mice showed the decrease during the administration and recovery of the weights were observed at 2 to 3 days after the completion of treatment. In the treated control groups, the infected mice began to show the pathologic findings 5 days after infection while the untreated mice began to show the findings 8 days after infection. Tissue damages in brain and lung occurred due to virulence of amoeba were more severe among treated mice than that in untreated control group. The above mentioned results suggest that the treatment with prednisolone weaken the resistance of mice against N. fowleri infection, and probably induce more severe primary amoebic meningoencephalitis. Especially severe pathological findings were shown in pre-treated group, compared with untreated group.
