Virus mediated induction of antibody independent cytotoxicity (VDCC) and enhancement of antibody dependent cytotoxicity (ADCC) in human lymphocytes in vitro

• Addition in vitro of small amounts of paramyxoviruses (Mumps or Sendai) to lymphocytes from healthy human donors induces a strong and non-selective cytotoxicity against a variety of target cells (VDCC, virus dependent cellular cytotoxicity). VDCC-like reactions are believed to play a role in vivo in the defense against virus infection and/or the causation of the tissue lesions associated with virus disease. The aim of this study was to investigate the mechanism of VDCC induction, its relationship to other lymphocyte mediated cytotoxic reactions and the nature of the effector cells involved.UV-inactivated virions induce VDCC as efficiently as live virus, indicating that it is not dependent on infection of either lymphocytes or target cells. Removal from the virions of the HN-surface glycoprotein carrying hemagglutination and neuraminidase activities abrogated VDCC. Removal of the F protein (F=fusion) was less efficient. When the lymphocytes were treated with solubilized HN- or F proteins, the HNprotein had full capacity to induce VDCC while the F protein was inactive. The importance of the HN-protein for VDCC was also supported by inhibition experiments with virus specific antibodies. Monoclonal anti-HN antibodies (mumps) inhibited VDCC whereas anti-F, anti-M (membrane) or anti-NP (nucleoprotein) antibodies did not. By using a panel of monoclonals directed to several distinct determinants of the HN-polypeptide, it was shown that at least 3 serologically defined structures of this protein were involved in VDCC induction. These structures appeared to be different from those involved in hemagglutination, hemolysis, neuraminidase activity and infectivity of the virus.When assayed at the level of the effector cell population (51Cr-release), VDCC was reflected by increased target cell lysis. At the effector cell level (single cell conjugate assay), VDCC was the expression of recruitment of both target-binding cells and target killing cells. In short term assays, virus treatment of the lymphocytes did not increase their recycling capacity, confirming that VDCC was primarily due to recruitment. Virus treatment of lymphocytes induces the release of interferon, known to enhance their cytotoxicity. VDCC induction appears to be independent of interferon. However, an activating effect of interferon in later phases of VDCC is not excluded.Cell fractionation experiments and single cell assays in combination with surface marker studies showed that VDCC effector cells were heterogeneous, including both large granular lymphocytes (LGL) and small to medium sized lymphocytes with Tcell characteristics. The cytotoxic effector cells recruited by virus comprised both lymphocytes bearing the LGL-associated HNK-1 antigen and lymphocytes bearing T-cell associated antigens. In absolute numbers, the majority of die effector cells had T-cell characteristics. However, the proportion of the latter differed for target cells of different types, suggesting that the target cells play a role in effector cell selection.VDCC is non-selective and is not MHC restricted, indicating that it is not mediated by specifically cytotoxic T-lymphocytes (CTL). Experiments with cord blood lymphocytes also showed that VDCC was not induced through specific or polyclonal activation by some viral material. VDCC induction is also independent of the participation of anti-target cell antibodies. However, virus treatment of the lymphocytes strongly enhanced their antibody dependent cytotoxicity (ADCC) both against VDCC susceptible tumor target cells and against VDCC resistant erythrocytic target cells. ADCC enhancement was a reflection of effector cell recruitment, primarily involving lymphocytes bearing T-cell markers. It was inhibited by monoclonal antibodies to the HN-protein. Taken together, these experiments showed that virus enhances ADCC by improving the effector cell target cell contacts necessary for cytotoxicity expression. This also results in a significant reduction in the amounts of antitarget cell antibodies required for the triggering of cytotoxicity.

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MEDICIN OCH HÄLSOVETENSKAP  -- Medicinska och farmaceutiska grundvetenskaper -- Cell- och molekylärbiologi (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Basic Medicine -- Cell and Molecular Biology (hsv//eng)

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