A dear friend of mine who is an intrepid post-doctoral researcher in the often murky, and full of much flow cytometry field of haematopoiesis sent me the following text from a recent gathering of some of the foremost immunologists in the field:
“People are now realizing that nutrition and immune function are closely linked. What a shocker!”
My friend comes from a nutritional biochemistry background, so this idea that the abilities of one’s immunocytes are closely linked to what you put in your body wasn’t especially mind-blowing to her. However, I could see why this could be so for others.
See, we think of the immune system as something that fights, kills, protects. It’s almost as if these cells are divorced from any other roles. However, that mindset is changing. And why not? The immunocytes in our body are inspiring: they make a variety of different pleiotropic factors, they are activated by many, many ligands/metabolites, they network with multifarious cell types like it was their job (it kinda is!), and so why wouldn’t they be involved in—wait for it—homeostasis?!
I recently read a piece about how γδ T-cells rely on recognizing metabolites from the mevalonate pathway to recognise rapidly proliferating cells—potential tumours—and kill them, thereby exerting tumour control. Inflammatory events are involved in the regulation of insulin responses and obesity. Phagocytes and a class of Treg cells regulate homeostatic responses and prevent autoimmunity and pathology at the level of the skin. Innate lymphoid cell classes provide a protection against immunosuppression and subsequent bacterial infections in the gut by modulating their functions under conditions of nutrient depletion. Interferon γ, that paragon of antiviral responses, also helps out in maintaining skin pigmentation. Alternatively-activated macrophages show up, and help regenerate muscle after acute muscle damage (think: exercise).
Why am I sharing these examples? Etymology tells us that “homoestasis” means “standing still.” We think of immunocytes as warriors, not a meditative, “standing still” population. That they do the legwork in processes that enable “standing still” can be thought of as, in a way, prophylactic. Immunocytes would seemingly be involved in making sure that things remain normal, happy and homeostatic rather than mobilizing a big immune response if/when something goes even slightly wrong, physiologically speaking. This makes sense because launching an immune response is costly to the body. In many ways, it is like going to war. Your legions of immunocytes are your troops, you have to feed them, keep them functional. This is energetically expensive, and makes you feel like crud most of the time. So why not ensure that things “stand still” rather than deal with hourly fresh Hells of physiological dysregulation?
To put it another way: the immune response will turn up when needed, but have you ever partied for 4 days straight, and then gone on a weekend binge? Hurts, don’t it? Turn up, and be legendary rather than being in a constitutive state of turnt!