This is a question that is often asked in my workshops. As it seemed in the 2014 study "Voluntary activation of the sympathetic nervous system and attenuation of the innate immune response in humans", and often described in media, those trained in the Wim Hof Method techniques, are able to fight off flu-like symptoms, due to a suppression of the immune system.
Whenever you talk about 'activation' or 'suppression' of the immune system, it seems to lead to incorrect reasoning.
For people suffering an auto-immune disease, the word 'activation' is understandably a word that triggers. They already have a very active immune system, so active that it has detrimental effects on their conditions. If their immune system is already attacking its own cells, an increase of this activity would not be warranted.
For people hearing 'suppression', equally bells go off. Supressing anything, let alone the body's defence system, doesn't seem logical. Suppression means that it would not work or work less effectively?
The right word to use when talking about the Wim Hof Method is: "boosting".
The method works in a comprehensive manner to boost the immune system, it surprises and activates!:
It decreases pro-inflammatory mediators TNF-a, IL-6 and IL-8. These are the proteins that signal the immune system that it needs to 'activate'.
It increases anti-inflammatory mediator IL-10 (with correlated higher levels of adrenaline). One of the functions, is that IL-10 regulates the TNF-α-converting enzyme. With lower levels of IL-10, pro-inflammatory marker TNF-a is not well regulated. This is the case with people that have Multiple Sclerosis (MS), for example.
Hormesis: what is clear is that there is an alarm bell going of in the body, which leads to a little switch: 1. Higher level of adrenaline, 2. higher level of ph (even up to 7.75, which quickly normalised after breathing.
Results of WIM HOF METHOD breathing:
TNF-a: 53% lower (this is the Master regulator of your Immune System)
IL-6: 57% lower
IL-8: 51% lower
IL-10: 194% higher
According to the researchers of the Radboud study, this result was probably due to the increase of epinephrine (adrenaline).
TNF-a (Tumor necrosis factor alpha) plays an important part in the immune response. If macrophages (certain white blood cells) detect an infection, they release TNF-a, that are responsible for signalling other immune cells, inducing an inflammatory response.
Interleukin (IL-)-6 is a protein much involved in the acute immune response at the site of inflammation, producing acute phase proteins, and dictates the transition in between acute to chronic inflammation. It also stimulates the production of T- and B-cells, supporting chronic inflammation.
Interleukin (IL-)-8 is a protein that signals and activates neutrophils (white blood cells). White blood cells are responsible for capturing and destroying invading bacteria.
Interleukin( (IL-)10 is also known as cytokine synthesis inhibitory factor (CSIF). It has a strong regulatory function with regards to the immune response. For example, it regulates the production of pro-inflammatory proteins, such as TNFa. It regulates the innate and adaptive immune responses, by limiting T-cell activation and surprising pro-inflammatory responses in tissues.
To read the whole research, go to the official Wim Hof Method page: