Pregnancy induced mammary tumor specific effector cells are present long after parturition in a breast cancer model in rats

Pregnancy is known to provide protection against 7,12 dimethylbenz[a] anthr acene-(DMBA) induced mammary carcinogenesis in rats. We observed in earlier studies that splenocytes of parous rats have significant cytotoxicity agai nst mammary tumor cells both in vitro and in vivo. However, it remains to b e established how long these cytolytic cells persist after parturition in p arous host. The present study was designed using parous rats, 36 or more da ys after parturition. We observed that fresh splenocytes from these rats ha d low cytolytic activity against mammary tumor cells. However, when these c ells were restimulated with irradiated mammary tumor cells in vitro, they h ad significantly higher cytotoxicity against mammary tumor cells. These stu dies show for the first time that pregnancy induced cytotoxic splenocytes a re present long after parturition and they can be restimulated in vitro to enhance the cytotoxic effect. (C) 2000 Elsevier Science Ireland Ltd. All ri ghts reserved.