Natural cytotoxic (NC) activity in basophilic cells: mediation by a NC-specific cytotoxic factor

Interleukin 3 (IL3) has recently been shown to be a mast cell/basophil growth factor. Based on the previous observations that IL3-dependent cells are capable of NC activity which are believed to be important in immunosurveillance, the authors attempted to define if the IL3-dependent NC cells were of basophilic origin. To approach this, the authors tested a murine IL3-dependent basophilic cell line and a rat basophilic leukemic cell line against various tumor targets in a 4h or 18h 51Cr release assay. Both basophilic cell types effectively lysed the NC target, WEHI-164, but not the NK targets, YAC-1, RLM1, RBL5. Moreover, triggering of the basophils by incubation at 37C with IgE-anti-IgE or IgE with specific antigen or by direct binding to anti-IgE receptor antibodies enhanced NC activity and at the same time induced the release of a soluble cytotoxic factor (CF). The CF lysed only WEHI but not YAC-1, RLM1 or RBL5 tumor cells, distinguishing it from NKCF. The release of the NCCF was dependent on the dose of the triggering agents, required extracellular Ca++, and was detected within 15 min of triggering. It has a MW of 43,000 as determined by gel filtration. Basophils, therefore, are not only involved in inflammatory responses but also in tumor immunity, via the NC effector mechanism