SISTER-CHROMATID EXCHANGE AND MICRONUCLEUS FREQUENCY IN HUMAN-LYMPHOCYTES OF 1,650 SUBJECTS IN AN ITALIAN POPULATION - I - CONTRIBUTION OF METHODOLOGICAL FACTORS

The influence of several methodological factors on mean values of sist er chromatid exchanges (SCEs) and micronuclei (MN) in peripheral lymph ocytes of 1,650 subjects was analyzed. Donors belonged to a general he althy population living in Pisa and in two nearby smell cities: Cascin a and Navacchia (Ca-Na). Blood samples were collected over a period of 29 months and processed in three different laboratories of the same i nstitute. Slides were analyzed by several scorers. Our data showed tha t lymphocyte proliferation indexes (Pls) and baseline mean values of S CEs were affected mainly by sampling period. This factor accounted for a percentage ranging from roughly 10% (Pisa) to 20% (Ca-Na) of total SCE variance and from roughly 10% (Pisa) to 13% (Ca-Na) of total Pls v ariance. A marginal effect was attributable to the different laborator ies involved (maximum 3% for SCEs and 7% For Pls). The sampling period variable included many sources of variability such as culture media b atches, fetal calf serum, PHA, BrdUrd, and seasonality. MN counts reve aled a more marked dependence on processing laboratories. This factor accounted For a percentage of roughly 10% (Pisa and Ca-Na) of total va riance, while the sampling period was marginally effective (about 1-4% of total variability). Because laboratories were equipped and sup pli ed with the same materials and consumables and technicians were rotate d constantly, the only variable ascertained was represented by the thr ee different models of CO2 incubators used for lymphocyte culturing. W hen ''month'' and ''incubator'' variables were considered jointly, exp erimental variability accounted For 15-20% of total variance, both for Pls and mean values SCEs and MN. The variability due to slide scoring was reduced by assigning each slide to five different scorers and mat ching low with high scorers in each group. Present data show that when the study is performed under these controlled conditions, about 20% o f total interdonor variability can be explained by experimental or sea sonal Factors. (C) 1998 Wiley-Liss, Inc.