Invariant Natural Killer T Cell Deficiency and Functional Impairment in Sleep Apnea: Links to Cancer Comorbidity.

STUDY OBJECTIVES: Emerging evidence links obstructive sleep apnea (OSA) with increased cancer incidence and mortality. Invariant natural killer T (iNKT) cells play an important role in cancer immunity. We hypothesized that patients with OSA have low number of circulating invariant natural killer T (iNKT) cells, which may also be functionally impaired. This study aims to evaluate the frequency of circulating iNKT cells in OSA. DESIGN: We evaluated the frequency of circulating iNKT cells by flow cytometry in 33 snorers being assessed for possible OSA. Using iNKT cell lines, we also evaluated the effect of exposure to hypoxia over 24 hours on apoptosis, cytotoxicity, and cytokine production. SETTING: Teaching hospital based sleep unit and research laboratory. PATIENTS: Thirty-three snorers were evaluated: 9 with no OSA (apnea-hypopnea frequency [AHI] < 5/h), 12 with mild-moderate OSA (AHI 5-30) and 12 with severe OSA (AHI > 30). MEASUREMENTS AND RESULTS: Patients with severe OSA had considerably fewer iNKT cells (0.18%) compared to patients with mild-moderate (0.24%) or no OSA (0.35%), P = 0.0026. The frequency of iNKT cells correlated negatively with apnea-hypopnea index (r = -0.58, P = 0.001), oxygen desaturation index (r = -0.58, P = 0.0003), and SpO2% < 90% (r = -0.5407, P = 0.005). The frequency of iNKT cells increased following 12 months of nCPAP therapy (P = 0.015). Hypoxia resulted in increased apoptosis (P = 0.016) and impaired cytotoxicity (P = 0.035). CONCLUSION: Patients with obstructive sleep apnea (OSA) have significantly reduced levels of circulating invariant natural killer T (iNKT) cells and hypoxia leads to impaired iNKT cell function. These observations may partly explain the increased cancer risk reported in patients with OSA.

Endogenous oils derived from human adipocytes are potent adjuvants that promote IL-1α-dependent inflammation.

Obesity is characterized by chronic inflammation associated with neutrophil and M1 macrophage infiltration into white adipose tissue. However, the mechanisms underlying this process remain largely unknown. Based on the ability of oil-based adjuvants to induce immune responses, we hypothesized that endogenous oils derived from necrotic adipocytes may function as an immunological "danger signal." Here we show that endogenous oils of human origin are potent adjuvants, enhancing antibody responses to a level comparable to Freund's incomplete adjuvant. The endogenous oils were capable of promoting interleukin (IL)-1α-dependent recruitment of neutrophils and M1-like macrophages, while simultaneously diminishing M2-like macrophages. We found that endogenous oils from subcutaneous and omental adipocytes, and from healthy and unhealthy obese individuals, promoted comparable inflammatory responses. Furthermore, we also confirmed that white adipocytes in visceral fat of metabolically unhealthy obese (MUO) individuals are significantly larger than those in metabolically healthy obese individuals. Since adipocyte size is positively correlated with adipocyte death, we propose that endogenous oils have a higher propensity to be released from hypertrophied visceral fat in MUO individuals and that this is the key factor in driving inflammation. In summary, this study shows that adipocytes contain a potent oil adjuvant which drives IL-1α-dependent proinflammatory responses in vivo.

Glucagon-like peptide 1 analogue therapy directly modulates innate immune-mediated inflammation in individuals with type 2 diabetes mellitus.

AIMS/HYPOTHESIS: Glucagon-like peptide 1 (GLP-1) is a gut hormone used in the treatment of type 2 diabetes mellitus. There is emerging evidence that GLP-1 has anti-inflammatory activity in humans, with murine studies suggesting an effect on macrophage polarisation. We hypothesised that GLP-1 analogue therapy in individuals with type 2 diabetes mellitus would affect the inflammatory macrophage molecule soluble CD163 (sCD163) and adipocytokine profile. METHODS: We studied ten obese type 2 diabetes mellitus patients starting GLP-1 analogue therapy at a hospital-based diabetes service. We investigated levels of sCD163, TNF-α, IL-1ß, IL-6, adiponectin and leptin by ELISA, before and after 8 weeks of GLP-1 analogue therapy. RESULTS: GLP-1 analogue therapy reduced levels of the inflammatory macrophage activation molecule sCD163 (220 ng/ml vs 171 ng/ml, p < 0.001). This occurred independent of changes in body weight, fructosamine and HbA1c. GLP-1 analogue therapy was associated with a decrease in levels of the inflammatory cytokines TNF-α (264 vs 149 pg/ml, p < 0.05), IL-1ß (2,919 vs 748 pg/ml, p < 0.05) and IL-6 (1,379 vs 461 pg/ml p < 0.05) and an increase in levels of the anti-inflammatory adipokine adiponectin (4,480 vs 6,290 pg/ml, p < 0.002). CONCLUSIONS/INTERPRETATION: In individuals with type 2 diabetes mellitus, GLP-1 analogue therapy reduces the frequency of inflammatory macrophages. This effect is not dependent on the glycaemic or body weight effects of GLP-1.

Cigarette smoke alters the invariant natural killer T cell function and may inhibit anti-tumor responses.

Invariant natural killer T (iNKT) cells are a minor subset of human T cells which express the invariant T cell receptor Vα24 Jα18 and recognize glycolipids presented on CD1d. Invariant NKT cells are important immune regulators and can initiate anti-tumor responses through early potent cytokine production. Studies show that iNKT cells are defective in certain cancers. Cigarette smoke contains many carcinogens and is implicated directly and indirectly in many cancers. We investigated the effects of cigarette smoke on the circulating iNKT cell number and function. We found that the iNKT cell frequency is significantly reduced in cigarette smoking subjects. Invariant NKT cells exposed to cigarette smoke extract (CSE) showed significant defects in cytokine production and the ability to kill target cells. CSE inhibits the upregulation of CD107 but not CD69 or CD56 on iNKT cells. These findings suggest that CSE has a specific effect on iNKT cell anti-tumor responses, which may contribute to the role of smoking in the development of cancer.