The HLA-A assay for detection of mutant lymphocytes has been modified, principally by incorporation of an overnight-incubation step which has resulted in improved immunoselection. For 83 estimations on cells from 21 normal individuals with a mean age of 35, the in vivo mutant frequency was 2.99 × 10-5 ± 1.48 × 10-5 (mean ± 1 SD). For 11 estimations on cells from 10 elderly individuals with a mean age of 78, the mutant frequency was significantly greater, being 7.16 × 10-5 ± 4.06 × 10-5. Similar results were obtained when HLA-A2 or HLA-A3 mutants were enumerated. Mutant frequency measured at the HLA-A locus is almost an order of magnitude greater than that measured at the hypoxanthine phosphoribosyl transferase locus, but at least the major part of this difference is likely to be due to factors other than a difference in genetic stability between the two loci.
- Hypoxanthine phosphoribosyl transferase