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Natural killer cell recognition of target cells expressing different antigens of vesicular stomatitis virus
Abstract:
Natural killer (NK) cells have the capability of lysing virus-infected, transformed, and embryonal cells, yet the nature of the target structure(s) recognized remains unclear. The availability of well-characterized temperature-sensitive (ts) mutants of vesicular stomatitis virus, defective in expression of individual viral-encoded polypeptides at the nonpermissive temperature (39 degrees C), offered an approach to elucidating NK-cell recognition of virus-infected cells. Target cells were infected with ts mutants in three functions: the viral surface glycoprotein (G protein; ts 045); the matrix (M) protein (ts G31, ts G33), and the polymerase (ts G11). Cells infected with wild-type virus and all ts mutants at the permissive temperature (31 degrees C) were killed by murine spleen cells. Similar to results on cytotoxic T lymphocytes, target cells infected by ts 045 defective in expression of G protein at 39 degrees C were not killed by NK cells. Unexpectedly, cells infected at 39 degrees C with the M-protein mutants also were not killed, although G protein was expressed at the cell surface. Target binding studies indicated that conjugates were not formed by cells infected with the ts mutants at the nonpermissive temperature. That expression of G protein was not sufficient for NK cell-mediated cytotoxicity was established in experiments in which a plasmid (pSVGL) containing the gene for vesicular stomatitis virus G protein was transfected into COS cells. Although G antigen was expressed on the plasma membrane, the cells were not lysed. These results suggest either that recognition of virus-infected cells depends on an appropriate conformation imparted to the viral G protein by association with the M protein or that NK cells can recognize alterations in the structure of the cell membrane induced by insertion of viral M and G molecules.
Insights
Natural killer (NK) cells recognize virus-infected cells, but the exact target structure is unclear. This study reveals that viral matrix protein, not just the G protein, is crucial for NK cell recognition of infected cells.
Area of Science:
- Immunology
- Virology
- Cell Biology
Background:
- Natural killer (NK) cells are crucial for innate immunity, eliminating virus-infected and tumor cells.
- The specific molecular targets recognized by NK cells on infected cells remain poorly defined.
- Vesicular stomatitis virus (VSV) temperature-sensitive mutants allow precise investigation of viral protein roles.
Purpose of the Study:
- To elucidate the viral components recognized by NK cells during infection.
- To determine if the viral glycoprotein (G protein) alone is sufficient for NK cell-mediated lysis.
- To investigate the role of other viral proteins, like the matrix (M) protein, in NK cell recognition.
Main Methods:
- Infection of target cells with temperature-sensitive mutants of vesicular stomatitis virus (VSV).
- Assessment of NK cell-mediated cytotoxicity at permissive (31°C) and non-permissive (39°C) temperatures.
- Expression of VSV G protein in COS cells via plasmid transfection to assess its sufficiency for lysis.
- Analysis of target cell binding to NK cells.
Main Results:
- NK cells failed to lyse target cells infected with VSV G protein mutants at the non-permissive temperature.
- Unexpectedly, NK cells also failed to lyse cells infected with VSV M protein mutants, despite G protein expression.
- Target cells infected with M protein mutants did not form conjugates with NK cells.
- Transfected COS cells expressing only VSV G protein were not lysed by NK cells.
Conclusions:
- NK cell recognition of VSV-infected cells is not solely dependent on the expression of the viral G protein.
- The viral M protein may be essential for proper G protein conformation or membrane insertion required for NK cell recognition.
- NK cell recognition might involve sensing broader alterations in the cell membrane induced by viral protein complexes.