The human lymphocyte in vitro cytogenetic assay: positive and negative control observations on approximately 30000 cells.
Data are presented from the cytogenetic analysis of the peripheral lymphocytes from 94 male and 15 female donors. However, a much smaller number of regular donors were selected for regular use. A total of 28674 cells were analysed and these acted as negative and positive controls in the in vitro human lymphocyte tests accumulated in this laboratory over a 6-year period. The significant observations were:. (1) in untreated and solvent control treated cultures (a) no chromosomal interchanges were observed in 21570 cells; (b) the incidence of dicentrics was less than 1 per 10000 cells; (c) other types of aberrations were seen with an increased frequency, chromosomal gaps being the most variable. (2) The reference clastogens mitomycin C and cyclophosphamide produced high and remarkably consistent yields of all types of aberrations. It is concluded that when screening compounds in vitro for new genotoxins, aberrations such as chromosomal interchanges and dicentrics (due to their rarity in negative control cultures) should be accorded greater significance than the several other types of aberrations routinely seen. These conclusions emphasize the value of maintaining and updating adequate historical control records.