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.
Klarmann
B
B
Institut für Medizinische Strählenkunde und Zellforschung, Universität Würzburg, Germany.
Wixler
V
V
Lorenz
R
R
Hempel
K
K
D000818:Animals; D005260:Female; D005805:Genes, MHC Class I / Q000528:radiation effects*; D006183:H-2 Antigens / Q000235:genetics* / Q000528:radiation effects; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics* / Q000528:radiation effects*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009154:Mutation; D013154:Spleen / Q000166:cytology / Q000528:radiation effects; D013601:T-Lymphocytes / Q000502:physiology* / Q000528:radiation effects*
D006183:H-2 Antigens; C024755:H-2K(K) antigen; D007041:Hypoxanthine Phosphoribosyltransferase