Early Activation of iNKT Cells Increased Survival Time of BALB/c Mice in a Murine Model of Melioidosis.

Melioidosis is an infectious disease caused by Burkholderia pseudomallei. High interferon gamma (IFN-γ) levels in naive mice were reported to mediate protection against B. pseudomallei infection. Invariant natural killer T (iNKT) cells can produce and secrete several cytokines, including IFN-γ. When iNKT cell-knockout (KO) BALB/c mice were infected with B. pseudomallei, their survival time was significantly shorter than wild-type mice. Naive BALB/c mice pretreated intraperitoneally with α-galactosylceramide (α-GalCer), an iNKT cell activator, 24 h before infection demonstrated 62.5% survival at the early stage, with prolonged survival time compared to nonpretreated infected control mice (14 ± 1 days versus 6 ± 1 days, respectively). At 4 h after injection with α-GalCer, treated mice showed significantly higher levels of serum IFN-γ, interleukin-4 (IL-4), IL-10, and IL-12 than control mice. Interestingly, the IFN-γ levels in the α-GalCer-pretreated group were decreased at 4, 24, and 48 h after infection, while they were highly increased in the control group. At 24 h postinfection in the α-GalCer group, bacterial loads were significantly lower in blood (no growth and 1,780.00 ± 51.21, P < 0.0001), spleens (no growth and 34,300 ± 1,106.04, P < 0.0001), and livers (1,550 ± 68.72 and 13,400 ± 1,066.67, P < 0.0001) than in the control group, but not in the lungs (15,300 ± 761.10 and 1,320 ± 41.63, P < 0.0001), and almost all were negative at 48 h postinfection. This study for the first time shows that early activation of iNKT cells by α-GalCer helps clearance of B. pseudomallei and prolongs mouse survival.

Decrease of spleen invariant natural killer T and natural killer cell numbers in Burkholderia thailandensis-infected C57BL/6 mice.

BACKGROUND: Burkholderia thailandensis is a non-pathogenic bacterium that is closely related to B. pseudomallei. Invariant natural killer T (iNKT) cells are innate lymphoid cells that play a role in bacterial infections; however the iNKT cells in B. thailandensis infections are still uncharacterized. OBJECTIVE: To study the cytokine production in α-galactosylceramide (α-GalCer)-stimulated lymphocytes from mouse organs. The numbers of spleen iNKT cells, natural killer (NK) cells, dendritic cells and macrophages in B. thailandensis- infected C57BL/6 (B6) mice were investigated. METHODS: Lymphocytes, obtained from mouse lungs, liver, and spleen, were cultured for 48 hours with α-GalCer, and their cytokine levels were determined. iNKT, dendritic, macrophage and NK cells in the spleen of B. thailandensis-infected B6 mice or iNKT knock out (KO) mice, stimulated with either phosphate-buffered saline (PBS) or α-GalCer, were analyzed by flow cytometry. This was also done in adoptive cell transfer experiments. RESULTS: Interferon gamma (IFN-γ) was predominantly produced in α-GalCer-stimulated mouse spleen and liver lymphocytes, while interleukin (IL)-13 was the main cytokine found in the lungs. B. thailandensis-infected mice had a significantly lower number of splenic iNKT, NK and dendritic cells, but not macrophages, compared to the control. Interestingly, the number of NK cells was significantly decreased in iNKT wild type and iNKT KO mice after B. thailandensis infection. The number of NK cells recovered by activation with α-GalCer or after adoptive transfer of iNKT cells into KO mice. The iNKT cell-mediated reduction of dendritic and NK cells might be related to infection by B. thailandensis. CONCLUSIONS: B. thailandensis decreased the number of iNKT and NK cells in the spleen of infected mice.

Invariant Natural Killer T (iNKT) cells response in human melioidosis.

BACKGROUND: Melioidosis is an infectious disease caused by Burkholderia pseudomallei. In infected mice, IFN-γ can provide protection against B. pseudomallei infection. Invariant Natural Killer T (iNKT) cells are a subpopulation of T lymphocytes, activated by recognition of glycolipid ligands such as α-Galactosylceramide presented by CD1d, produce and secrete several cytokines, including IFN-γ and IL-4. The response of iNKT cells in human melioidosis was then investigated. OBJECTIVE: To determine the iNKT cells response in human melioidosis. METHODS: The number of human iNKT cells and its activation states were investigated in sepsis melioidosis patients compared with healthy controls using flow cytometry. The iNKT cells activation was confirmed in vitro using heatkilled B. pseudomallei with normal peripheral blood mononuclear cells. The components induced iNKT cell were also determined using different concentration of B. pseudomallei lipopolysaccharide (LPS), heat-killed B. pseudomallei treated with or without DNase, RNase, or proteinase. RESULTS: The number of human iNKT cells was significantly lower while the percentage of activated iNKT cells was higher in sepsis melioidosis when compared to control. In addition, B. pseudomallei can stimulate human iNKT cells in vitro. Heat-killed B. pseudomallei could activate iNKT cells but not relate to nucleic acid, proteins, or LPS. CONCLUSIONS: We found for the first time that the iNKT cells were activated during B. pseudomallei infection in human. However, the roles and the mechanism of iNKT cells during early state of infection needed to be further investigated.

New Genetically Manipulated Mice Provide Insights Into the Development and Physiological Functions of Invariant Natural Killer T Cells.

Invariant natural killer T (iNKT) cells are a unique T cell subset that exhibits characteristics of both innate immune cells and T cells. They express Vα14-Jα18 (Trav11-Traj18) as an invariant chain of the T cell receptor (TCR) and are restricted to the MHC class I-like monomorphic antigen presenting molecule CD1d. iNKT cells are known as immune regulators that bridge the innate and acquired immune systems by rapid and massive production of a wide range of cytokines, which could enable them to participate in immune responses during various disease states. Thus, Traj18-deficient mice, Cd1d-deficient mice, or iNKT cell-overexpressing mice such as iNKT TCRα transgenic mice and iNKT cell cloned mice which contain a Vα14-Jα18 rearrangement in the TCRα locus are useful experimental models for the analysis of iNKT cells in vivo and in vitro. In this review, we describe the pros and cons of the various available genetically manipulated mice and summarize the insights gained from their study, including the possible roles of iNKT cells in obesity and diabetes.