The IL-6 system and its interaction with chronic low-grade inflammation and high intensity intermittent exercise.

The IL-6 system is key in the development of chronic low-grade inflammation. It is known to be upregulated in response to acute exercise and lowered at rest after exercise training. IL-6 has both anti- and pro-inflammatory properties and moderation of this cytokine could alleviate chronic low-grade inflammation which is associated with obesity and Type 2 diabetes mellitus (T2DM). This thesis investigated the interplay between inflammation, glycaemic control and high intensity intermittent training (HIIT) - an exercise regimen that has been shown to yield many health benefits. There was a greater increase in IL-6 after an acute bout of HIIT than continuous moderate intensity exercise, where external work was matched (Chapter 4). Although sIL-6R and the IL-6/sIL-6R complex were both significantly increased after acute exercise there were no differences between HIIT and moderate intensity exercise. In response to 2 weeks HIIT there was a significant reduction in IL-6 and increase in IL-6R in adipose tissue in overweight and obese males (Chapter 5). It was also determined that IL-6R present in adipose tissue is at least partly composed of the membrane-bound IL-6R isoform (Chapter 6). Reductions in circulating sIL-6R, the IL-6/sIL-6R complex, MCP-1 and adiponectin, as well as a decrease in waist circumference and increase in peak oxygen uptake during exercise were also induced after 2 weeks HIIT (Chapter 5). Young adults with T2DM (< 40 y) displayed elevated levels of inflammatory proteins in comparison to lean controls, however there were no significant differences in comparison to obese controls (Chapter 7). In conclusion, the findings of this thesis demonstrate that acute and repeated bouts of HIIT have positive effects on the inflammatory profile in the circulation and adipose tissue, particularly in relation to the IL-6 system. It should be determined if HIIT is an achievable mode of exercise for patient populations, including T2DM patients, in order to downregulate the inflammatory profile