Role of myokines in exercise and metabolism
What it's saying is that when you exercise, various chemical messengers called cytokines are produced. These cytokines act on different cells to activate (or inhibit) them and can have profound effects on different things, particularly immunity. This group and others have thought that skeletal muscle produces specific cytokines - hence the term myokines. Paracrine effects are those on the cells around them. I'm not sure exactly why they use the term endocrine as that's really about hormones being released from organs and they probably meant autocrine, which means it acts on itself. IL6 is a cytokine that has lots of effects. Recently it has been shown to mediate effects which lead to the chronic inflammatory and/or
autoimmune diseases (IBD, Rheumatoid arthritis, MS). IL8 is also known as a chemokine because it is involved in chemotaxis - the recruitement of other cells to a certain place to engage in an immune response. IL8 is a chemokine that attracts neutrophils. IL15 is a cytokine that is normally present in the gut, but is involved in the activation of T cells. The review looks back at the literature on cytokine production and it's effects on metabolism and immunity.
(Ok I can 't let this go....I am an enthusiastic amateur in all this but the above paragraph was written by a friendly immunologist that I know (very well))
The Conclusion of the paper says:
The recent identification of skeletal muscle as an endocrine organ that produces and releases myokines expands our knowledge on how the nervous, endocrine, and immune systems contribute to the maintenance of homeostasis, also when challenged by physiological demands. Given that skeletal muscle is the largest organ in the human body, our discovery of contracting muscle as a cytokine-producing organ opens the possibility for a whole new paradigm: skeletal muscle is an endocrine organ that by contraction stimulates the production and release of cytokines, which can influence metabolism and modify cytokine production in tissues and organs.
The interesting thing with this is that it starts to point towards a mechanism by which exercise can be "good for you". Or indeed bad for you if you do too much ( I am told that IL-6 is not seen as wholly beneficial). Hence exercise can be both anti inflammatory and proinflammatory, if you do too much.
So we are back to the power law idea that I mentioned. You need to exercise...but you should intersperse a few high intensity bits with lots and lots of low intensity stuff and languid rest.