The invariant NKT cell subset in anti-viral defenses: a dark horse in anti-influenza immunity?

iNKT cells, a small subset of αβ TCR+ T cells, are capable of producing large amounts of cytokines upon activation through their TCR. Unlike conventional T cells that express highly diverse TCRs, iNKT cells express a glycolipid-reactive invariant TCR-α chain paired with a limited number of β chain(s). These cells recognize glycolipid antigens when presented on CD1d molecules found on APC or other cells. Although the immunoregulatory roles of iNKT cells in the context of autoimmune disease are fairly well characterized, several lines of evidence highlight the importance of this cell type in immune responses against microbial insults caused by bacterial, viral, and parasitic pathogens. Recent studies that have investigated the role of iNKT cells in immune responses against influenza virus have suggested an important role for these cells in innate defense mechanisms as well as antibody- and cell-mediated responses. This review highlights the important contributions of iNKT cells to immune responses against viral pathogens with particular emphasis on immunity to influenza infections.