Isolation and quantification of class 1 MHC gene mutants in mouse T cells by immunoselection with a magnetic cell sorter (MACS)

Studies of thioguanine-resistant lymphocytes induced by in vivo irradiation of mice

The frequency of Hprt-deficient lymphocytes in mice after in vivo gamma irradiation, has been found to vary as a function of time elapsed after exposure and irradiation dose. The frequency of mutant lymphocytes in spleen was determined using an in vitro, clonogenic assay for thioguanine-resistant T-lymphocytes. Mice were exposed to single doses of 0-400 cGy from cesium-137 or to eight daily doses of 50 cGy. The time to maximum-induced mutant frequency was 3 weeks. The dose response was strikingly curvilinear at 3-5 weeks after irradiation, but less precisely defined for 10-53 weeks after exposure, being fit by either linear or quadratic dependence. Three weeks after eight daily 50 cGy exposures, mutant frequency was elevated above controls and mice exposed to 50 cGy (which were not distinct from the nonirradiated controls), but only 17% in that of mice given a single 400 cGy fraction. This fractionation effect and the curvilinearity of the early dose-response curve suggested that saturation of repair increased the yield of mutations at higher acute doses. The decline of spleen mutant frequency in mice observed between 5 and 10 weeks after irradiation may reflect selection against some mutants. The marked variation of mutant frequency, as a function of time after irradiation and of dose rate, emphasize the need to evaluate these variables carefully and consistently in future studies.

Methodological study of cell separation with domestic immunomagnetic beads

To establish the method of cell separation with domestic immuomagnetic beads, three methods were investigated. Direct method, SPA method and Biotin-Avidin method were applied to separate cell strain Hut-78 and CD4 positive cells. Separation rate of strain Hut-78 was more than 90% in direct method. Detachment rate with papain was over 95%. Cell activity was well retained. SPA method and Biotin-Avidin methods were also effective, but the direct method was superior to the other two techniques. Before separated by the direct method, CD4 positive cells constituted 46.4% +/- 6.4% of mononuclear cells (MNC), but in eliminated suspension there was only 6.2% +/- 2.3% CD4 positive cells left. In the separated part, 80.6% +/- 7.2% of the cells combined with the beads. It is concluded that the direct method in separating cells had high sensitivity and specificity.

Positive selection of NK1.1+ cells on a magnetic cell separator (MACS)

Natural killer (NK) cells are involved not only in resistance to tumors and infection, but also in some transplantation reactions. A specific, inexpensive method for purifying large numbers of NK cells is often required. All NK cells in H-2b mice express the surface marker NK1.1. We report a method for positively selecting NK1.1+ spleen cells from normal and Poly I:C-stimulated C56Bl/6 mice using a magnetic cell separation technique known as MACS. Our results show that cytotoxic activity directed at YAC-1 target cells by normal and Poly I:C-stimulated spleen cells could be increased five-fold using this method. We also found that spleen cells from mice given Poly I:C could lyse NK-resistant, BW1100 target cells, and that this activity could be increased two-fold. Flow cytometry analysis of Poly I:C-stimulated, MACS enriched, NK1.1+ spleen cells revealed the presence of two subpopulations: one consisting of LGL and the other consisting of smaller, agranular lymphocytes (SAL). After enrichment, the percentage of NK1.1+ spleen cells increased from 69% to 91% in the LGL subpopulation and from 33% to 73% in the SAL subpopulation. These results clearly demonstrate the effectiveness of the MACS technique for purifying large numbers of NK1.1+ cells for both flow cytometric and functional analyses.

Mutant frequency at the H-2K class 1 and HPRT genes in T lymphocytes from the X-ray-exposed mouse

The frequency of H-2Kk and HPRT-deficient T cells was measured in the H-2Kb, kDd,k genotype mouse 8-10 weeks after X-ray exposure at doses up to 6 Gy to compare the mutant frequency (MF) of an autosomal gene with that of an X-chromosomal gene. H-2K mutants were enriched by magnetic cell separation (MACS) using the H-2Kk-specific monoclonal antibody H100.5/28 and were isolated by limiting dilution cloning. Finally, the mutant phenotype was verified by flow cytometric analysis in a representative number of clones. The frequency of HPRT-deficient T cells rises from 2.5 x 10(-6) at 0 Gy to a maximum of 1.13 x 10(-4) at 4 Gy, and decreases to 2.9 x 10(-5) at 6 Gy. The H-2K- MF in the non-irradiated mouse was 8.4 x 10(-7). It increases with dose to a maximum of 8.1 x 10(-6) at 4 Gy and declines to 3.3 x 10(-6) at 6 Gy. The H-2K- MF measured depends on the monoclonal antibody used for the isolation of mutants. In a pilot study with another H-2Kk-specific monoclonal antibody (11.4.1), the spontaneous MF was four times higher than in experiments with the H100.5/28 monoclonal antibody. The expression of other class 1 antigens was investigated in H-2K- clones. The H-2Dd antigen had also disappeared in six of 41 clones from irradiated animals. This gene is situated at a distance of 1500 kb from the K-locus. The H-2Kb antigen was present in every investigated clone. In the discussion a model is presented that explains the shape of the dose-response curve of MF by selection against mutants in vivo systems under homeostasis. The results of the present investigation indicate that observed X-ray mutagenicity depends on many factors and that several genes have to be explored before reliable risk estimates are possible.