GD3 ganglioside antibody augments tumoricidal capacity of canine blood mononuclear cells by induction of interleukin 12

Monoclonal antibody R24 recognizes ganglioside GD3 expressed on the cell surfaces of some tumor cells and on a subset of human T lymphocytes. Binding of R24 to these lymphocytes induces proliferation, cytokine production, and activation of intracellular signaling pathways. In the current report, we investigated expression of gangliosides by canine mononuclear immune cells and studied the ability of antiganglioside antibody to activate these cells using tumor cell killing as a measure of activation. A subset of canine monocytes, but not lymphocytes, was found to express gangliosides GD3 and GD2 as determined by the binding of monoclonal antibodies R24 and 14.G2a, respectively. Only R24 augmented the tumoricidal potential of fresh canine peripheral blood mononuclear cells (PBMCs) against tumor cell lines that did not express surface gangliosides GD3 or GD2. The augmenting effect of R24 on PBMC-mediated tumor cytotoxicity required cooperation between monocytes and lymphocytes because there was no enhancement of cytotoxicity mediated by R24 combined with either monocytes or lymphocytes individually. The enhancing effect of R24 on canine PBMC-mediated tumor cytotoxicity was blocked by anti- interleukin (IL)-12 neutralizing antibody, suggesting that R24 binding to monocytes triggered IL-12 release, contributing to the observed tumor killing effects. Reverse transcription-PCR confirmed that the binding of R24 to canine monocytes induced transcription of mRNA for canine IL-12. These data indicate that monocytes can be activated for tumoricidal responses through a membrane structure associated with ganglioside GD3 triggered by the binding of R24 and that the mechanism for enhanced cytotoxicity is due to the production and secretion of IL-12.