Inhibition of in vitro lymphoproliferative responses by in vivo passaged rat 13762 mammary adenocarcinoma cells. I. Characteristics of inhibition and evidence for an infectious agent.

Small numbers of X-irradiated 13762 cells added as third-party cells to mitogen response assays or mixed lymphocyte cultures caused a significant reduction in viability of the cocultivated lymphocytes, and completely inhibited the expected lymphoproliferative responses. Results showed that the factor(s) responsible for the inhibitory effect was preserved after ultrasonic disruption of the tumor cells, could be sedimented by ultracentrifugation, and was sensitive to treatment with ultraviolet light. Further, cytopathic effects could be serially propagated using cell-free supernatants obtained from sonicated 13762 tumor cells. The results suggest that the 13762 adenocarcinoma line, as carried in vivo in this laboratory, harbors an infectious particle which can affect the proliferative responses of lymphocytes in vitro.