Anti-tumour efficacy of mouse spleen cells separated with Dolichos biflorus lectin (DBA) in experimental pulmonary metastasis of B16 melanoma cells.

Anti-tumour effector cells were generated through 4 days culture of normal C57BL/6 splenocytes in a medium containing concanavalin A supernatant and then fractionated with Dolichos biflorus lectin (DBA) into DBA+ (agglutinable with DBA) and DBA- (non-agglutinable with DBA) cells. The DBA- cells, infused intravenously into mice together with B16 melanoma cells, or adoptively transferred into mice 3 days after the injection of B16 cells, caused a marked decrease in the number of lung nodules, while the DBA+ cells exerted no effect. On the other hand, the DBA+ cells exhibited higher cytolytic activity in vitro than the DBA- cells in short-term 51Cr-release assays. Then, we analysed the mechanism of the strong anti-tumour activity of DBA- cells in vivo. We found that DBA- cells showed higher response to recombinant interleukin-2 (rIL-2) than DBA+ cells and proliferated very well with a small amount of IL-2. In addition, DBA- cells adhered more strongly to lung endothelial cells than DBA+ cells in response to rIL-1 or rTNF. Furthermore, DBA- cells produced larger amounts of macrophage activating factor (MAF) including IFN-gamma when cultured with B16 melanoma. Taken together, our results show that DBA- cells are effective in reducing experimental pulmonary metastases not only by the direct lytic activity but also by the indirect killing activity through the activated macrophage.