A Killer Cell Protective Antigen Expressed by MHC-Unrestricted Killer Hybridomas

We have established MHC-unrestricted killer hybridoma cell lines. A monoclonal antibody (mAb K2D) described in this study destroyed some of these killer hybridoma cell lines when added to their cultures. This destruction of cells required cell-to-cell contact, indicating that the killer hybridoma cells were killed by others of the same killer hybridoma(fratricide). Based on the facts that the killer hybridoma used did not express FcγRIII, and that F(ab′)2fragments of mAb K2D also induced the cell destruction, antibody-dependent cellular cytotoxicity (ADCC) was excluded from a possible mechanism underlying this fratricidal killing. The molecular characteristics of the antigen recognized by mAb K2D and the results obtained by sequential immunoprecipitation led us to conclude that mAb K2D recognizes the Ly-49G2 molecule already described as a member of the Ly-49 family of NK cell inhibitory receptors. Thus, these results suggest that the killer hybridoma cells are protected by the inhibitory signals delivered by Ly-49G2 from killing each other. In addition, we found that mAb K2D recognizes an additional Ly-49-like antigen other than Ly-49G2 on the killer hybridoma, which may reflect the complexity of the Ly-49 family proteins.