Fig 1: Detection of intraspecies cell mixtures using PCR amplification. Cross-contamination between frequently used cell lines of different species is easily detected using PCR-based species identification assays. Depending on the organism, the species-specific primers target either the cytochrome oxidase I or the cytochrome B genes. In this example, mixtures of human (NCI-H522 [H522]; ATCC® CRL-5810™) and mouse cells (LL/2 (LLC1); ATCC® CRL-1642™) were created at various ratios and were analyzed via multiplex PCR. The presence of human cells was detected using a set of primers specific for the human COI target (a), while the presence of the mouse contaminant cells was detected using a multiplex PCR targeting 11 non-human species (cat, Chinese hamster, rhesus monkey, horse, cow, African green monkey, rat, goat, dog, New Zealand rabbit, and mouse) (b). Human band 391 bp; mouse band 150 bp; internal control 70 bp. Abbreviations used: M Invitrogen 100 bp ladder; NTC no template control. These results, together with STR profiling for the cell line mixtures, are also summarized in Table 2.