The indirect fluorescent antibody test was performed to demonstrate the antibody production in the rabbits immunized with free-living amoebas; Acanthamoeba culbertsoni and Naegleria fowleri, and antibody titer changes by immunization duration. Rabbits were immunized with Acanthamoeba culbertsoni and Naegleria fowleri which were cultured axenically in CGVS medium. For experiments, rabbits were divided into two groups; small dose group received 10(4) intravenously with live or dead free-living amoebas trophozoites as an immunizing dose three times with one week interval, and large dose group received 10(6) live or dead trophozoites respectively. The control group received physiologic saline or medium for culture of free-living amoebas intravenously. Antiserum was collected 4 times at interval of 3 days in the first 10 days, and also up to 2 months later. In the group immunized with live Acanthamoeba culbertsoni, fluorescent antibody titer was higher than in the group of dead one, and also in the large dose group than in the small dose group. Antibody titer of anti-Naegleria fowleri serum in the large dose group showed no difference by the source of amoeba antigen; live or dead. But in the small dose group, antibody titer was higher in the immunized with live Naegleria fowleri than in the group with dead one. No cross reactivity was demonstrated between the Acanthamoeba and Naegleria. And no cross reaction was observed when the free-living amoebas antigens were tested against human sera of amoebiasis, paragonimiasis and clonorchiasis.
