Just a few weeks of high-fat food are apparently enough to trigger unhealthy immune processes in our abdominal fat, as a study shows. Accordingly, the high-calorie diet causes special defense cells to migrate into the fatty tissue and accumulate there. They are then activated and increasingly release messenger substances that, in extreme cases, can derail the metabolism and promote diabetes and other diseases.
It has been known for a long time that excess abdominal fat in particular increases the risk of disease. Because in this fatty tissue accumulated between the organs of the abdominal cavity, metabolic processes take place that promote inflammation and, in the long term, can promote diabetes, cardiovascular diseases and metabolic syndrome. However, not everyone who carries a lot of belly fat is equally susceptible to these consequences.
Defense cells in view
Researchers led by Susanne Stutte from the Ludwig Maximilian University of Munich (LMU) may have discovered a possible reason for this. Because, as they found out, a particularly high-calorie or high-fat diet plays an important role in potentially pathogenic immune processes in abdominal fat. The key players here are the so-called plasmacytoid dendritic cells (pDCs).
These rounded defense cells normally react to viruses and other potentially dangerous changes by releasing inflammatory messenger substances. “The formation of plasmacytoid dendritic cells is primarily restricted to the bone marrow, from where they migrate into the blood and lymphatic system and patrol through the body,” the scientists explain. Recent studies have shown, however, that these defense cells can also migrate into abdominal fat.
How exactly this happens and how diet influences the behavior of the pDC immune cells, Stutte and her team have now used mice to investigate in more detail. To do this, they gave mice either normal food or high-fat, high-calorie food and following three weeks they used fluorescent markers and other cell-biological methods to investigate what was happening in the animals’ visceral fat.
Abundance of immune cells in abdominal fat
The analyzes revealed that following just three weeks of eating a high-fat diet, the mice not only had increased abdominal fat, there were also striking immunological changes in this fatty tissue. As the team found, under the influence of the high-calorie diet, pDC defense cells increasingly migrate into the visceral fat and collect there in lymphoid tissue-like cell clumps, so-called fat-associated lymphoid clusters (FALC), which can become immunologically highly active.
In the high-calorie fed mice, the number of pDC immune cells in these lymphoid cell clumps of abdominal fat increased more than threefold in a short time, the research team found. A clear accumulation of dendritic defense cells was also found in other organs. “Our study revealed a systemic pDC response with increased cell counts in the blood, liver, spleen, bone marrow and visceral fat on a high-fat diet,” the researchers said.
Scan mode and messenger substance release activated
But that’s not all: under the influence of the high-fat diet, the pDC immune cells, which normally remain on “standby”, were also activated. “In vivo imaging showed an acceleration in the rate of migration of these cells following a high-fat meal,” reports the team. “This indicates that they are transitioning from a stationary sleep mode to active scanning mode.”
At the same time, the immune cells begin to release significantly more messenger substances, including large amounts of the pro-inflammatory interferon-1. “This rapid release of interferon-1 by the pDC immune cells is characteristic of the body’s early response to metabolic imbalances,” explains the team. When this process continues, it leads to metabolic deregulation, which can lead to diabetes and metabolic syndrome.
Daily diet plays a role
These findings suggest that it’s not just belly fat that affects our immune system and health. Instead, what we eat every day also plays a role in his reaction. “This previously unknown modulation of pDC cells by a high-fat diet sheds new light on how our daily diet influences the complex interaction between the immune system and adipose tissue,” state Stutte and her colleagues.
At the same time, however, these new insights might also provide clues for therapeutic approaches. “If you might prevent pDCs from getting into the fat, you might possibly also prevent the resulting secondary diseases,” explains Stutte’s colleague Barbara Wallog. (The Journal of Immunology, 2022; doi: 10.4049 / jimmunol.2100022)
Source: Ludwig Maximilian University of Munich