Regulation of the cytotoxic effect of human 'normal killer cells' on tumor cell lines by neuraminidase-treated T-lymphocytes

Subpopulations of peripheral blood lymhocytes (PBL) from healthy individuals were separated according to their capacity to form various rosettes and tested for their cytotoxic activity on cell lines of urinary bladder and breast carcinomas. The subpopulation exerting the highest natural cytotoxic activity was characterized by the presence of cell surface Fc-receptors and by the lack of receptors for sheep red blood cells and for C'3 on their surface. Treatment with vibrio cholera neuraminidase (VCN) increased the cytotoxicity of unseparated PBL to a level twice as high as that of untreated PBL. The attachment of T-lymphocytes to tumor monolayers was increased several fold after VCN-treatment, while the attachment of other lymphocyte subpopulations was not. Evidence is presented that the augmentation of the cytotoxicity of PBL following VCN-treatment results from the interaction of VCN-treated T-lymphocytes, attached to target cells, with normal killer cells. It is suggested that augmentation of the activity of killer cells by T-lymphocytes may play a role in antitumor defense mechanisms.