A Novel Functional T Cell Hybridoma Recognizes Macrophage Cell Death Induced by Bacteria: A Possible Role for Innate Lymphocytes in Bacterial Infection

Abstract

We have established a novel TCRαβ (TCRVβ6)+CD4−CD8− T cell hybridoma designated B6HO3. When the B6HO3 cells were cocultured with bacterial-infected J774 macrophage-like cells, IFN-γ production by B6HO3 cells was triggered through direct cell-cell contact with dying J774 cells infected with Listeria monocytogenes (LM), Shigella flexneri, or Salmonella typhimurium that expressed the type III secretion system, but not with intact J774 cells infected with heat-killed LM, nonhemolytic lysteriolysin O-deficient (Hly−) LM, plasmid-cured Shigella, or stationary-phase Salmonella. However, the triggering of B6HO3 cells for IFN-γ production involved neither dying hepatoma cells infected with LM nor dying J774 cells caused by gliotoxin treatment or freeze thawing. Cycloheximide and Abs to H-2Kd, H-2Dd, Iad, CD1d, TCRVβ6, and IL-12 did not inhibit the contact-dependent IFN-γ response, indicating that this IFN-γ response did not require de novo protein synthesis in bacterial-infected J774 cells and was TCR and IL-12 independent. Thus, in an as yet undefined way, B6HO3 hybridoma recognizes a specialized form of macrophage cell death resulting from bacterial infection and consequently produces IFN-γ. Moreover, contact-dependent interaction of minor subsets of splenic αβ T cells, including NKT cells with dying LM-infected J774 and bone marrow-derived macrophage (BMM) cells, proved to provide an IFN-γ-productive stimulus for these minor T cell populations, to which the parental T cell of the B6HO3 hybridoma appeared to belong. Unexpectedly, subsets of γδ T and NK cells similarly responded to dying LM-infected macrophage cells. These results propose that innate lymphocytes may possess a recognition system sensing macrophage cell “danger” resulting from bacterial infection.