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What is Inflammation?

Inflammation [8] is one of those words that people use without really thinking about its actual meaning. So today we’re going to take a bit of a break from the blood lipid [9] series to cover inflammation. In later posts, I’ll dig deeper into how the inflammatory response works with stuff like exercise and heart disease, but for now, I’ll just get the basics out there.

Existence is suffering, according to certain schools of thought. I don’t know that I’d go quite that far, but I would emphatically state that anyone who spends a modicum of sentient time in the space time continuum we call existence is gonna experience some unpleasantness. A bump on the knee, a bacterial infection, an acute injury, a persistent illness, a death of a loved one, a broken heart. It’s a big and often angry world that doesn’t necessarily care about you, and something’s gotta give. When that happens and the sanctity of our bodies is interrupted by pain, injury, or illness, our bodies respond with inflammation.

There’s that word again: inflammation. It pops up quite often in our circles, usually playing either the starring role, absolutely killing it as a supporting actor, or stealing the show with a cameo appearance in some malady or another. Heart disease, obesity, depression [10], arthritis (and any  -itis, really), autoimmune diseases, insulin resistance – all classics worthy of accolades (although tonsillitis totally got robbed in last years Oscars), and all linked to inflammation, sometimes even causally. So inflammation must be terrible, right? It must be completely and unequivocally a negative trait, kinda like how our body evolved to manufacture cholesterol [11] to kill us. What, didn’t you know that coronary heart disease confers a survival advantage?

Jokes aside, the fact that inflammation is a common, natural, innate response to injury/pain/illness/stress is a hint that there’s probably something necessary about it. It’s not some accident, nor is it our body hell-bent on making life miserable for itself. On the contrary: inflammation is our body’s way of saying it isn’t gonna take the affront of injury or illness lying down. It’s not a passive spectator totally reliant on the kindness of Pfizer and Walgreens and an ice pack to get it out of a jam. Although you wouldn’t think it, what with the barrage of altruistic allknowing medical experts and commercials both touting some essential pharmaceutical, our bodies can actually heal themselves. And the first responder, so to speak, is the inflammatory process. That’s right. Pain, swelling, redness, and that radiating sense of warmth that we feel at the site of an injury or illness don’t manifest by accident or for kicks. That’s inflammation [12], and it’s essential to our very existence in a world of hurt.

First up, acute inflammation.

The initial response to a pathogen or an injury is acutely inflammatory. In other words, it is brief, lasting several days or less. All sorts of things can cause an acute inflammatory response. Here are a few:

Things happen pretty fast in an acute inflammatory response and involve several different players, including the vascular system (veins, arteries, capillaries and such), the immune system, and the cells local to the injury. First, something painful and unpleasant happens; choose one of the above injury options. Then, pattern recognition receptors (PRR) located at the injury site initiate the release of various inflammatory mediators, which in turn initiate vasodilation (or widening of the blood vessels). This allows increased blood flow to the injury site, which warms the site, turns it the familiar red, and carries plasma and leukocytes to the site of the injured tissue. The blood vessels become more permeable, thus allowing the plasma and leukocytes to flow through the vessel walls and into the injured tissue to do their work. Emigration of plasma into tissue also means fluid buildup, which means swelling. At the same time, the body releases an inflammatory mediator called bradykinin which increases pain sensitivity at the site and discourages usage of the injured area. These sensations – heat, redness, swelling, pain, and a loss of function – are annoying and familiar, but they are absolutely necessary for proper healing.

Allow me to explain why the four primary symptoms of acute inflammation are important:

These symptoms both indicate and enable inflammation (and, thus, healing), but what’s the deal with inflammation being linked with all those chronic illnesses – like obesity, heart disease, and depression? How does something normal and helpful go haywire and become implicated in some of the most crushing, tragic diseases of our time?

When inflammation becomes chronic and systemic, when it ceases to be an acute response, when it becomes a constant low-level feature of your physiology that’s always on and always engaged, the big problems arise. The inflammatory response is supposed to be short and to the point. I mean, just look at its responsiveness. Go twist an ankle (don’t, not really) and watch how fast it swells up and gets warm to the touch. It isn’t meant to be on all the time.

And because a big part of inflammation is breaking the tissue down, targeting damaged tissue and invading pathogens, before building it back up, the inflammatory response has the potential to damage the body. That’s why it’s normally a tightly regulated system, because we don’t want it getting out of hand and targeting healthy tissue. But if it’s on all the time, regulation becomes a lot harder.

All these inflammatory mediators and their effects are short-lived and require constant propagation to keep going. The only thing that keeps it flowing is sustained or subsequent injury to the site, so a little cut that heals in a couple days will need to get infected or reopened if the inflammatory cascade is going to continue. This usually doesn’t happen in developed countries. Wounds don’t fester, limbs aren’t hacked off because they got infected, and we don’t live with as many parasites as we used to. There’s no exogenous bacterial epidemic laying waste to the population by invading our bodies and stimulating an inflammatory response that never quite ends (although the Jaminets would suggest that persistent infections are more common than we might think [13]). No, there must be another explanation. There’s got to be another stressor, or stressors, that are doing two things: inducing the inflammatory response and hanging around in the environment as a constant feature.

I’m going to fire off a few things that both induce inflammation and tend toward prevalence in developed countries. You let me know if anything sounds familiar to you.

See what I mean? Since we’re set up for acute stressors requiring an acute inflammatory response, all this other low-level, evolutionarily-discordant, superficially mild stuff throws us off and sets us up for a lifetime of chronic inflammation.

Anyway, that’s all for today. I hope it was a learning experience. If you have any questions about inflammation, leave them in the comments and I’ll try to work them into future installments. Take care and Grok on! [35]