Trehalose 6,6'-dimycolate (TDM), an immunomodulator, potentiates non-specific resistance in mice to influenza virus infection. When mice were injected intravenously with TDM, the striking proliferation of a minority of T-lymphocytes bearing gamma/delta T-cell receptors (gamma delta T-cells) that accumulated in granulomatous lungs was thought to be associated with the maintenance of acquired resistance to lethal influenza virus infection. To clarify the cellular basis of the defence against influenza virus, mice were depleted of gamma delta T-cells, alpha/beta (alpha beta) T-cells, or natural killer (NK) cells by in vivo administration of corresponding antibodies prior to influenza virus infection. The depletion of gamma delta T-cells significantly abrogated the augmented resistance of TDM-treated mice to infection, as did depletion of either alpha beta T-cells or NK cells. To gain insight into the functional ability of gamma delta T-cells, we evaluated the cytotoxic activity of this T-cell subset against a panel of target cell lines that were stably transfected with the influenza virus haemagglutinin (HA) gene from A/PR/8/34(H1N1) and A/Aichi/2/68(H3N2) strains. The gamma delta T-cells from TDM-treated mice showed profound cytotoxicity against the target cells expressing HA of either the H1 or H3 subtype, in a non-major histocompatibility complex-restricted manner. Taken together, these results indicate that gamma delta T-cells play a non-specific role, in conjunction with alpha beta T-cells and NK cells, in protecting mice against influenza virus infection, and that the recognition and destruction of HA-expressing target cells by the activated gamma delta T-cells is one of the steps involved in this anti-influenza virus immunosurveillance.


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