Increases and perturbations in thymocytes forming spontaneous rosettes during viral and chemical oncogenesis in hamsters

Normal hamster thymocytes were repeatedly observed to form spontaneous (E) rosettes with sheep erythrocytes. The percentage of rosetting thymocytes was subject to reproducible, seasonal variation, fluctuating from consistently high values of up to 17.2% in winter months to <5% in late summer and fall. The number of rosette-forming cells (RFC) increased during the induction of primary, virally, and chemically induced tumorigenesis irrespective of the seasonal variation. Infection of neonate hamsters with SV40 or adenovirus 31 caused significant increases of 50% or more of RFC cells in the thymuses of individual hamsters assayed as early as 2 weeks after infection. Treatment of weanling hamsters with the carcinogen dimethylbenzanthracene (DMBA) produced significant increases in thymocyte RFC at the time of primary tumor appearance. The increases in RFC induced by carcinogenesis appear to be limited to a particular subset of thymocytes defined by assay in dextran compared to a larger population of RFC which could be determined by assay in the presence of heat-inactivated, SRBC-absorbed serum. Induction of primary tumors had the most effect in increasing RFC within the dextran-defined thymocyte subset, as challenge with tumor cells only effected slight RFC increases.