The natural killer cell activity of splenocytes and TBC, active NK cells, recycling capacity of natural killer cells were observed by means of both the 51Cr-release cytotoxicity assay and single cell cytotoxicity assay against YAC-1. C3H/HeJ mice were infected intranasally with 1 x 10(4) or 1 x 10(5) trophozoites of pathogenic Acanthamoeba culbertsoni. The infected mice showed mortality rate of 34% in 1 x 10(4) group and 65% in 1 x 10(5) group, and mean survival time was 16.40 +/- 3.50 and 13.20 +/- 4.09 days respectively. The cytotoxic activity of natural killer cells of the 2 groups was significantly higher than that of non-infected mice from the 12th hour to the 2nd day after infection, showing the highest on the first day. On the 10th day after infection, the cytotoxic activity of natural killer cells was significantly suppressed as compared with that of the control. There was no significant difference in NK cell cytotoxicity between two infected groups. The target-binding capacity and active NK cells of natural killer cells in 1 x 10(5) trophozoite infected mice was significantly increased on the 12th hour and the first day after infection as compared with the control group. Maximal recycling capacity (MRC) was not changed during the observation period. The present results indicated that the elevation of natural killer cell activity in the mice infected with A. culbertsoni was due to elevation of target-binding capacity and increased active NK cells of natural killer cells, and not due to the maximal recycling capacity of the individual NK cell, and there was no difference between two experimental dose groups.
