NKT cells: Friend or foe during viral infections?

Abstract

NKT cells are innate-like T lymphocytes that are found in rodents and primates. They are non-conventional T cells restricted by the CD1d molecule that presents self and exogenous glycolipids. NKT cells are unique in their ability to promptly secrete copious amounts of cytokines such as IFN-c and IL-4. Once activated, NKT cells can provide maturation signals to downstream cells, including DC, NK cells, and lymphocytes, thereby contributing to both innate and acquired immunity. Accordingly, NKT cells can influence a wide array of immune responses, including tumor surveillance, maintenance of self-tolerance and anti-infectious defenses. Studies performed with NKT-cell-deficient mice have shown that these cells are critical for the clearance of various pathogens. During bacterial infections, NKT cells can be activated either indirectly by DC or directly by bacterial lipid antigens presented by CD1d. Although viruses do not contain lipid antigens, NKT cells have also been implicated in antiviral responses. The capacity of NKT cells to regulate viral immune-surveillance, either constitutively or post-activation, makes them an attractive clinical target. In this review, we summarize recent publications dealing with the functions and relevance of NKT cells in the context of viral infections, both in murine models and in humans. (Table 1). Immune evasion by impairing CD1d-mediated antigen presentationSeveral viruses have developed immune-evasion strategies that impair CD1d-mediated antigen presentation, suggesting a role for NKT cells in antiviral responses. Infection by Kaposi sarcomaassociated herpes virus down-regulates cell-surface CD1d expression [6]. This effect is due to two viral modulators of immune recognition proteins, which ubiquitinate the cytoplasmic tail of CD1d and thereby accelerates CD1d endocytosis. HSV type 1 (HSV-1) infection leads to defective CD1d recycling from the endosome to the cell surface, due to its trapping in the late endosomal compartment and resulting in reduced cell-surface expression [7]. Likewise, HIV type 1 (HIV-1) down-regulates CD1d expression by increasing CD1d internalization from the cell [50,56,[57][58][59][60] Eur. Mini-Review

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Interleukin-1 Family Cytokines as Mucosal Vaccine Adjuvants for Induction of Protective Immunity against Influenza Virus

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