Win Hof has actually had legitimate studies done where he has proven he can activate his immune system with his mind

The wikipedia article on wim hof where they quoted the study seems a lot more believable:

" . . . forceful respiration results in increased sympathetic innervation and glucose consumption in intercostal muscle, generating heat that dissipates to lung tissue and warms circulating blood in the pulmonary capillaries. Our results provide compelling evidence for the primacy of the brain (CNS) rather than the body (peripheral mechanisms) in mediating the Iceman's [Wim Hof's] responses to cold exposure.[28]"

By hyperventillating you are just flexing your intercostal muscle and that's warming your body. If you sat there flexing your quads or your core over and over you would probably get a similar sensation.

https://en.wikipedia.org/wiki/Wim_Hof

That's in response to cold. He has also been tested for effects on immune response:

"It was shown that this individual was able to voluntarily activate the sympathetic nervous system through a self-developed method involving meditation, exposure to cold, and breathing techniques. This resulted in increased catecholamine and cortisol release and a remarkably mild innate immune response during experimental endotoxemia compared with more than 100 subjects who previously underwent experimental endotoxemia."

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4034215/

Perhaps it is bunk science? I'm not qualified to say. I personally did find the methods have been helpful.

Given the brain’s regulatory role in virtually every aspect of homeostasis, I’m surprised that folks are surprised that by mental exercises autonomous functions can be influenced if not controlled. Wim Hof is interesting, but any Hindu can tell you that yogis have been performing similar feats for millennia.

this is a great point re the brain's regulatory role. thanks for sharing.

can you recommend terms to google to learn more about what mental exercises yogis do and can achieve immunologically?

I think its worth nothing that the Wim Hof method also includes both cold exposure and breath holds, both of which I believe are physiologically linked to the immune response.

Though the article does seem to suggest that focusing your thoughts in a particular way could be involved as well. Pretty cool!

It seems the immune response of Wim Hof method occurs as a result of intentionally creating an adrenaline response in the body. Apparently other breathing techniques do this prior to Wim Hof (Tummo breathing). Andrew Huberman, a neuroscientist at Stanford talks about the science of this https://youtu.be/JPX8g8ibKFc?t=2161 (at that timestamp he talks specifically about adrenaline breathing)

Pierre Capel explains this in this video: https://youtu.be/hJ7zbsRM0-c

When you breath like Wim Hof CO2 levels in your blood change and this will have an effect on your pain response. CO2 lowers and the pH raises.