Researchers have been demonstrating over the past couple of years that excess fat tissue contributes to chronic inflammation, with the role of macrophage cells being particularly important. Here's more on that topic from EurekAlert!: "the inflammatory chemokine known as CXCL5 rises and falls with obesity and subsequent weight loss in humans. (Chemokines are structurally related signaling proteins that are secreted by cells.) ... Fat tissue known as white adipose tissue (WAT) is primarily involved in energy storage in the form of triglycerides and energy release in the form of free fatty acids, Fajas' team explained. However, WAT is more than a fat storage organ; it also secretes numerous other factors with roles in both health and disease. ... [CXCL5] is expressed at high levels in WAT, particularly in immune cells known as macrophages. Moreover, they report that CXCL5 is dramatically increased in the blood of people who are obese compared to those who are lean. Those CXCL5 levels drop when obese people lose weight and are also lower in obese individuals that continue to respond to insulin than in those who are insulin resistant. .... the [receptor for CXCL5] is active outside of muscle, in cells that line blood vessel walls and in the lung and intestine, for example. Therefore, increased CXCL5 circulating levels as observed in obesity could lead to other problems, including atherosclerosis and other inflammatory diseases."