Adenosine phosphorylase activity in a mutant HEp-2 cell line contaminated with Mycoplasm hyorhinis.

Metabolic studies in HEp-2/MP,MIR cells (an adenosine kinase, hypoxanthine phosphoribosyltransferase negative mutant) indicated the presence of adenosine phosphorylase activity. This activity, unknown in established mammalian cell lines, resulted in the glycosidic cleavage of both adenosine and the antiviral drug arabinosyladenine. The activity was observed readily in the presence or absence of the adenosine deaminase inhibitor conformycin. Isopycnic separation of [3H] thymidine-labeled DNA species in CsCl density gradients resulted in the appearance of two distinct peaks. The heavier peak coincided with [14C]thymidine-labeled marker DNA of human origin, whereas the lighter peak was within the range associated with mycoplasmal DNA. Testing by commercial laboratories confirmed the presence of mycoplasma in HEp-2/MP,MIR cells. The contaminant was identified as Mycoplasma hyorhinis, a porcine mycoplasma. Following gamma-irradiation (3000 rads) to block cellular mitosis, the mucoplasma-contaminated HEp-2/MP,MIR cells were cocultivated with mycoplasma-free wild-type HEp-2 cells which did not exhibit adenosine phosphorylase activity. Following serial cocultivation in a medium designed to favor the survival of the wild-type cells, adenosine phosphorylase activity was found in the previously uninfected cells. Studies of this nature emphasize the need for investigators to carefully monitor their cell lines for mycoplasma.