The gut-immune axis

What do gut bacteria contribute to?

The literature describes several contributions. These involve overlapping and reinforcing processes, not isolated mechanisms:^[1][2]

• The development of the immune system, particularly in the first years of life.^[3]
• Training immune cells to respond appropriately.^[2]
• Distinguishing harmless stimuli — such as food and the body's own bacteria — from potentially harmful ones.^[1]
• Regulating inflammatory responses, in both strength and duration.^[4]
• Maintaining a healthy gut barrier.^[6]

How do gut bacteria communicate with the immune system?

Gut bacteria are in continuous contact with immune cells. This communication runs through several biological routes simultaneously.^[4]

One well-studied route involves short-chain fatty acids such as butyrate, which are produced when gut bacteria ferment fibre. These substances appear to influence various immune processes and the energy supply of gut wall cells.^[5]

Research also describes a role for regulatory T cells, which help determine when an immune response is dampened, and for cytokines: signalling molecules used by immune cells to communicate with one another.^[4] The gut epithelium and gut barrier form the interface where this exchange takes place, while receptors on immune cells — including Toll-like receptors — recognise microbial structures. Other microbial metabolites are also being studied as signalling molecules to the immune system.^[5]

This is a highly complex biological network. These processes cannot be viewed in isolation, and the extent to which they play a role in any given individual cannot be precisely determined with current knowledge.

Gut barrier and immune function

The gut wall not only absorbs nutrients but also has a protective function: it keeps out what does not belong in the bloodstream. Gut bacteria appear to contribute to maintaining that barrier, partly by nourishing gut wall cells and via the mucus layer that covers the gut wall.^[6]

Research describes that disruption of this balance can coincide with changes in immune activity. Scientists are currently investigating how these processes contribute to various inflammatory diseases, including inflammatory bowel disease.^[7]

There is still considerable uncertainty about the precise sequence of events: it is often not possible to determine whether a disrupted barrier is the cause or the consequence of inflammation. Research into this is ongoing.

Gut microbiome and chronic inflammation

Disruptions of the gut microbiome — referred to in the literature as dysbiosis — are associated in research with changes in inflammatory processes.^[8]

Research suggests associations with a wide range of conditions. Attention focuses in particular on inflammatory bowel disease, autoimmune diseases, metabolic disorders and chronic low-grade inflammation.^[9]

There are indications that the microbiome plays a role here, but most studies describe associations rather than direct causality.^[8] The precise cause-and-effect relationship is still being investigated. A measured difference in composition therefore cannot be used to draw conclusions about the onset or course of a disease.

What can a gut microbiome analysis add?

A gut microbiome analysis provides insight into the composition of the personal gut ecosystem: which groups of micro-organisms are present and in what proportions.^[10]

That information can be used as a starting point for personalised nutrition advice, lifestyle guidance, support for gut health and personal guidance by a doctor. The analysis is one piece of the puzzle alongside symptoms, medical history and previous investigations.

An analysis does not provide a diagnosis of immune disorders and cannot establish or rule out an autoimmune or inflammatory disease.