When someone has a disease but no symptoms, how is their immune system behaving differently than someone who does have symptoms?
In: Biology
For most respiratory diseases, the symptoms we experience are a direct result of our immune system trying to fight the disease:
Inflammation/swelling/congestion – Good: more blood flow to send immune cells and nutrients to fight at the infected site. Bad: swelling can damage surroundings and reduce function (blocked airway or immobile swollen joint).
Runny nose – Good: diseases get caught in the liquid or mucus rather than infect more cells. Bad: can cause blockages if not physically expelled.
Cough – Good: expelling the above. Bad: lack of mucus can cause a dry cough that further injures the infection site. Also increases chance of transmitting the disease.
Fever – Good: heating up the body to slow down the disease spread. Bad: too much heat can hurt the organs in your body, especially the brain.
Would HRV pick this up?
The ELI5 answer: it depends on the number of things we get in our systems, how quickly more are being made, and how much damage they are doing to us. When someone’s immune system is “good,” our bodies kill everything or stop its spread through the body. When there are too many, we use stuff like snot to catch the bad stuff, fevers to cook the bad stuff, and coughing to remove the bad stuff we caught. When it gets really really bad, we have special cells that make sticky pieces to bog down invaders and make them easier to clear. People with no or little symptoms are able to stop the invader from spreading, so there is less need for stuff to catch the invaders on a large scale.
The more complicated answer:
Immune systems have two components.
The first is the innate immunity, or the immunity that attempts to work on any foreign invaders, and the adaptive immunity, the one we associate with antibodies. It may actually be better to refer to these two systems as “General defense” and “Specific defense” because innate immunity is a general defense system, while adaptive immunity (antibodies) are very specific.
The symptoms we see from viral or bacterial infection is almost always caused by the body itself, not the invader. When an invader gets in, it wants to first and foremost get energy from its surroundings so that it can replicate and make more. That is its goal. Its goal is not to kill the host (usually…), but if it does its whatever. It’s goal is to get a good meal to feed its children and make more children. Obviously the body doesn’t want this. It worked hard to get those nutrients and without them, the cells will die. In innate immunity, there are several types of defense cells that work to stop the spread of invaders and remove the bad ones from the system.
The first line of defense in the body are natural barriers, including mucosal linings in the throat and nose, the skin itself, and many others. They attempt to stop pathogens at first. Even our spit has enzymes in it that can kill some invaders.
The second line of defense, when that pathogen invades, are the immune cells. Some immune cells can recognize things that don’t belong. They will then kill them. Other times, like with viruses that invade cells, the immune cells are able to tell the difference between infected and non-infected cells. This is because cells that are infected are actually able to either reduce the amount of “we’re ok!” signal on their surface, or able to display a “WE”RE FUCKED PLZ HELP” on their surface. These cells can then be killed to protect other cells.
As the immune response occurs and invaders are recognized, they start up the “ok we’re infected” process. Chemicals are released by dead cells or by the immune cells to tell the body to start an inflammatory response. This inflammatory response is what causes secretion of lots of snot, starts fevers, etc. This is what we characterize as “being sick.” Most of the time, however, if cells aren’t being killed at a large rate and the immune cells clear them up, the inflammation response is very localized, so we don’t see much of it. This is also one of the reasons that for most vaccines we don’t get “sick” from them – there isn’t enough cell death to trigger a prolonged inflammatory response. Some vaccines may cause this because there is enough produced from immune cells, but it is greatly reduced.
But somehow, you ingested a “huge” amount of the virus or bacteria. They’re everywhere in your throat. Cells are starting to die left right and center, and the innate immunity can’t keep up. Your throat is now flooded by the inflammation chemicals. They start to increase, until cells in your body say, “inflammation response time!” and trigger a fever, trigger increase of immune cell production and release, increase snot production, etc. You’re now ‘sick’ because there is a fuckton of assholes stealing your cell’s energy.
When the innate immunity is having trouble controlling the spread of invaders, it says, “heh we’re fucked” and other cells get into action. They’re also called the “stranger danger” response, which I think is very funny. They recognize the invaders are really bad, and start calling for production of a more specific response because this is really bad. This causes two main things: production of antibodies and creation of ‘memory.’ Antibodies are essentially a stick with a fork on the end. The fork is like a puzzle piece that only fits with another specific piece on the invader/affected cells/toxin produced by invader. When the two pieces fit together, it sticks.
Because there are a lot of antibodies sticking to invaders, the invaders have a lot more trouble doing what they’re normally able to do. Ever see Incredibles with the sticky ball scene on Mr. Incredible? Antibodies kind of do that. They make it a lot harder for invaders to spread, they make the invaders much easier to see by immune cells, and they make it much easier for immune cells to kill them.
The second thing adaptive immunity does it make it so there are receptors that can more easily recognize the invader so that instead of a slow buildup to immunity, the body jumps straight to it. The body can instantly recognize, “hey, it’s that terrorist again. GO TIME!” and more quickly produce an inflammatory response and antibodies. This drastically reduces the spread of the invader and the time it takes to remove the invader. This is also why sometimes people can have no symptoms even if they’re sick – their immune system stops the viruses spread long before it gets to the point where a large-scale inflammatory response is needed.
What is incredibly important to realize is that the body DOES NOT WANT to perform an immune response if it does not have to. Immune responses use a lot of energy and often impair normal function of the rest of the body. There is the whole idea of energy versus defense trade-off where when an immune response occurs, the rest of the body has less energy to use on other processes. This is often why some illnesses “knock us on our ass” because cellular energy is being used for the immune response. This is often why sleep and proper nutrition when you’re sick is vital.
Believe it or not, you are bombarded with hundreds to thousands of potential illnesses EVERY DAY! It just so happens that there is not enough of the virus/bacteria for them to effectively colonize and escape from the immune system. The innate immune system is effective in almost every single case of infection. If it was not, we would be so overburdened by making antibodies we would be permanently tired and most likely dead. It’s the ones that get too bad that causes the adaptive immune response.
Extra fun fact, there are cases where the immune system mistakes an invader as a danger because there are so many of them, even when they’re not dangerous. This is the case for allergies. There are so many “invaders” that the immune system can’t keep up, so it starts an inflammatory response. Because the body can’t get rid of the invaders, the adaptive immunity is also called into play. It creates a memory of this awful invader that the body can’t get rid of, so that every other time it meets this invader, it causes the immune response much quicker. It can recognize it like any other pathogen. The only problem is it’s not really dangerous – the body just can’t tell the difference. And because the allergens are everywhere (like pollen), they are going to have a lot of immune responses.
Ninja edit: This post is probably about COVID-19, so I’ll explain why it’s dangerous. It spreads really quickly without people showing symptoms because most people are able to quite easily deal with it. The issue is for older people, because most (maybe all?) cases of death were caused by pneumonia. When you get older, your immune system gets weaker, so the virus is able to spread more effectively. This causes a larger scale inflammatory response in people who can’t stop its spread. It spreads further, such as into your lungs, where it activates the inflammatory response. This causes snot and fluids to go into your lungs to stop the spread of virus. Ironically, this results in pneumonia. Younger people are fine because they can clear the fluid out of their lungs without much issue. Older people, smokers, etc., have lung weakness/damage, so they have more issues clearing the fluid from their lungs. They fill up with more and more fluid, until the body can’t get oxygen it needs. This is the predominate cause of death. Weirdly, very young people seem to be completely ok with the virus. The hypothesis is they are unable to mount an incredibly large inflammatory response, so they don’t really see the effects of the virus. However, this is only a hypothesis.
My thing with this, while most of the answers are solid, is that no one mentioned “viral/bacterial load”. Someone without symptoms may just have a very small number of the organism (virus or bacteria) and so it flies under the radar. The immune system hasn’t recognized it as a threat yet or if it has, it takes a little bit for your body to alert the proper authorities to start drawing up an immune response to the invader. There is a whole chain of things that happen and items that are synthesized depending on what type of threat the body is dealing with. So while yes, people with symptoms are actively fighting off the illness, the other person with no “illness” or symptoms isn’t aware that they are under attack just yet.
I have this issue- I have a very low white blood cell count which means I often get viruses, but my body has no ability to fight off the virus, so I get ill but without the same symptoms (eg runny nose, coughing, sneezing etc).
The reason you get those symptoms is your body trying to get rid of the virus or bacteria or infection- it’s not the symptoms that are the illness, those symptoms are your body trying to save you. It’s doing this by whatever means, flush it out of your system via your bodies fluids. If you have a low/zero white cell count, your body simply wont put up a fight and the illness runs rampant.
What happens? Well this varies as to how badly affected a person is. On a milder level, I am laid low, very tired and unable to do very much. I feel the cold a lot so going out can feel impossible or even leave me shivering on a warm day where the weather is 25 degrees. It can feel physically very draining to do very much at all anyway, even getting out of bed can feel beyond possible, if it is possible to push yourself through this, you find the speed and/or capacity to do as much is diminished.
Fact is, if your body has no ability to flush things out, it will try to use what capacity it does have (not possible for some eg those going through chemotherapy for example that have zero white cell count) whilst you are laid low, perhaps too tired or in too much pain to move very much, it takes some of the demands away from what immune system you do have and means your body can knuckle down on battling at all.
Some people don’t win that battle. They suffer heart attacks, they lose consciousness, they develop additional long term conditions, some become very depressed and take their own lives (when I say you are laid low, all of your energy gone it has a dramatic effect on your mind and your outlook.) When you are recovering, it often means you carry the illness for a great deal longer than you otherwise would and it can also sit in smaller amounts in your system, your body unable to fully get rid of it. It can and often does return at a more developed stage some time later and kill you.
My personal experience? Long term anorexic. My weight is low due to malnutrition, my white cell count is below the healthy or acceptable level. I still have some white cell count though- others I know have a lower level than me, I know there is always worse. Yes I do want to recover, no there is not treatment for everyone. I don’t have the money to pay for what I need, it’s this or no life at all. And yes I feel worried, very, about the current news.
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