Paradoxically high resistance of natural killer T (NKT) cell-deficient mice to Legionella pneumophila: another aspect of NKT cells for modulation of host responses

Innate immunity against Legionella pneumophila during pulmonary infections in mice

Legionella pneumophila is an etiological agent of the severe pneumonia known as Legionnaires' disease (LD). This gram-negative bacterium is thought to replicate naturally in various freshwater amoebae, but also replicates in human alveolar macrophages. Inside host cells, legionella induce the production of non-endosomal replicative phagosomes by injecting effector proteins into the cytosol. Innate immune responses are first line defenses against legionella during early phases of infection, and distinguish between legionella and host cells using germline-encoded pattern recognition receptors such as Toll-like receptors , NOD-like receptors, and RIG-I-like receptors, which sense pathogen-associated molecular patterns that are absent in host cells. During pulmonary legionella infections, various inflammatory cells such as macrophages, neutrophils, natural killer (NK) cells, large mononuclear cells, B cells, and CD4+ and CD8+ T cells are recruited into infected lungs, and predominantly occupy interstitial areas to control legionella. During pulmonary legionella infections, the interplay between distinct cytokines and chemokines also modulates innate host responses to clear legionella from the lungs. Recognition by NK cell receptors triggers effector functions including secretion of cytokines and chemokines, and leads to lysis of target cells. Crosstalk between NK cells and dendritic cells, monocytes, and macrophages provides a major first-line defense against legionella infection, whereas activation of T and B cells resolves the infection and mounts legionella-specific memory in the host.

[iNKT cells participate in the exacerbation of systemic candidal infection]

Candida species are one major causal microorganism of hospital acquired bloodstream infections associated with high mortality. Phagocytes like neutrophils in innate immunity and CD4 T cells in acquired immunity have a major role in host defense immune response. It has been recently found that a type of innate-like lymphocyte called NKT cells respond against various organisms but its role in candidal infection remained unknown. Thus, we analyzed the role of NKT cells in the immune response against systemic candidiasis using mice deficient of NKT cells. In vivo studies revealed that invariant NKT cells play a limited role for controlling systemic candidal infection. On the other hand, studies looking at the role of glycolipid-activated NKT cells during candidal infection revealed that candida-infected mice injected with glycolipid had shorter survival period and greater number of fungal colonies in the kidney accompanied with reduced number of neutrophils in the blood and bone marrow. Surprisingly, glycolipid-mediated exacerbation of candidal infection was absent in IFNγ deficient mice. Co-infection of candida with intestinal commensals caused exacerbated infection in which IFNγ played a critical role in impairing fungal elimination. These results suggest that the excessive IFNγ released from candida and bacterial co-infection is a critical factor in worsening candidal infection.

Invariant natural killer T cells: boon or bane in immunity to intracellular bacterial infections?

Invariant natural killer T (iNKT) cells represent a specialized subset of innate lymphocytes that recognize lipid and glycolipid antigens presented to them by nonclassical MHC-I CD1d molecules and are able to rapidly secrete copious amounts of a variety of cytokines. iNKT cells possess the ability to modulate innate as well as adaptive immune responses against various pathogens. Intracellular bacteria are one of the most clinically significant human pathogens that effectively evade the immune system and cause a myriad of diseases of public health concern globally. Emerging evidence suggests that iNKT cells can confer immunity to intracellular bacteria but also inflict pathology in certain cases. We summarize the current knowledge on the contribution of iNKT cells in the host defense against intracellular bacterial infections, with a focus on the underlying mechanisms by which these cells induce protective or pathogenic reactions including the pathways of direct action (acting on infected cells) and indirect action (modulating dendritic, NK and T cells). The rational exploitation of iNKT cells for prophylactic and therapeutic purposes awaits a profound understanding of their functional biology.

Role of type 1 natural killer T cells in pulmonary immunity

Mucosal sites are populated by a multitude of innate lymphoid cells and "innate-like" T lymphocytes expressing semiconserved T-cell receptors. Among the latter group, interest in type I natural killer T (NKT) cells has gained considerable momentum over the last decade. Exposure to NKT cell antigens is likely to occur continuously at mucosal sites. For this reason, and as they rapidly respond to stress-induced environmental cytokines, NKT cells are important contributors to immune and inflammatory responses. Here, we review the dual role of mucosal NKT cells during immune responses and pathologies with a particular focus on the lungs. Their role during pulmonary acute and chronic inflammation and respiratory infections is outlined. Whether NKT cells might provide a future attractive therapeutic target for treating human respiratory diseases is discussed.

Inhibitory function of interferon on hepatocarcinogenesis

OBJECTIVE

We examined the growth-inhibitory effect and the mechanism of action of type I interferon (IFN) in human liver cancer cell lines in vitro and in vivo.

METHODS

We examined the growth-inhibitory effect of 5 types of type I IFN preparations (e.g., pegylated, nonpegylated IFN-alpha, and IFN-beta) used for the treatment of chronic hepatitis C in 13 liver cancer cell lines in vitro. After liver cancer cells were transplanted into nude mice, various doses of IFN preparations were subcutaneously administered, and the antitumor effect was examined.

RESULTS

The growth-inhibitory effect of each preparation was different, but IFN-beta expressed the strongest effects in vitro. Induction of an inhibition of cell cycle progression at the G(1), S or G(2)/M phase with or without apoptosis was the mechanism of action of IFN. IFN preparations induced a dose-dependent decrease in tumor volume and weight by inducing tumor cell apoptosis in vivo, and tumor growth was effectively suppressed even at the clinical dose for chronic hepatitis C treatment. The antitumor effect of pegylated IFN was significantly stronger than that of nonpegylated IFN.

CONCLUSION

The data suggest potential clinical application of pegylated IFN for the prevention and treatment of hepatocellular carcinoma.