Why does our body reject other people’s donated organs and require immunosuppressants to be taken but getting someone else’s blood is ok?

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Why does our body reject other people’s donated organs and require immunosuppressants to be taken but getting someone else’s blood is ok?

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Anonymous 0 Comments

Getting someone else‘s blood can cause an immune reaction.

Of course im gonna have to oversimplify, the immune system is quite a complex thing.

Your immune system has a pretty big stockpile of different antibodies for different diseases. Whenever a cell from your immune system bumps into another cell it checks if it‘s something your body has antibodies for.

Blood can have a lot of different surfaces, and you can classify it by that. If the surface of your own blood and the donated blood is similar your immune system can‘t tell the difference. If you receive blood from a non-matching group your immune system will react and kill the donated red blood cells.

With organs you have a shit ton of different surface molecules and a whole lot of different cells. You simply cannot find a donor organ where each cell appears to the immune system as the bodies own cells. You can‘t group organs like you can with blood because they are far more complex.

Anonymous 0 Comments

First of all: getting someone else’s blood is not “okay”, they need to find a donor that matches your blood type otherwise your body would “reject” the blood (and that could kill you).
Secondly, donated blood stays in your system for two weeks maximum. A donated organ stays in your body much longer, hence there’s more opportunity for your immune system to attack the donated organ.

Anonymous 0 Comments

Before you are born, your body takes a sort of census of everything that is “you”. This is how your immune system knows how to identify what it is protecting, and what it is protecting you *from*. Based on that census, and a sort of index of all of the proteins your body knows how to synthesize, your immune systems creates specialized cells that go off and hunt for things that are “not you”.

Blood is pretty simple. While there are a lot of them, all your regular blood cells are pretty close to identical. Even so, while you can get blood from other people, they have to have a compatible Type and Rh factor, or your body absolutely will reject and attack it. It causes big clots to form, and it absolutely can be lethal if not treated, though it isn’t always. Even if you get a transfusion of the wrong blood type, the cells don’t live very long, and as a percentage of your blood volume, it’s not very much. Even if your body didn’t reject them, they’d be completely gone in a few weeks.

Organs are waaaay more complicated. Instead of only one kind of cell, it can have dozens, or hundreds that do specialized things. That’s a lot more chances that your immune system is going to decide that the new organ is “not you”, and decide to attack it.

Blood cells only live a couple of months, but your new organ has to work for the rest of your life. If all you transplanted blood gets killed, we’ll, meh. If all the cells in your new kidney get killed – that’s very bad.

Then there is how your immune system works. Once it decides that you’re new organ is the enemy, it goes back and teaches other immune cells how to make cells that are specifically made to attack those organ cells. As more and more of your immune cells encounter your organ cells, and learn to make cells to attack it, the number, and effectiveness of cells that target you organ increase. Without immune suppression, In not very long, your immune system will be destroying the organ cells faster than your new organ can replace them, or your body can clean up the mess made by killing them.

Anonymous 0 Comments

Trying to keep it at ELI5 level: there are two important parts to know about to understand this.

1. your immune system looks on cells for information/markers to say it belongs there, like an ID badge. Wrong ID badge means it’s killing time

Blood cells have very simple ID badges. There are only a small number of types of blood around, so it’s relatively simple to test recipient against donor blood to see if the recipients immune system would attack and kill it.

For matching organs, cells often have more information on them, think of “the id badge” being more elaborate. The chances of finding someone who has the exact matching “id badge” is small, but you might get someone who has a very similar “badge”. With the similar badge you get low level attack from the immune system. (If there wasn’t any matching the attack is aggressive and just won’t work for transplanting).
Add in the immunosuppressants and that attack falls even lower.

2. How long the blood or organ is going to last.

We are constantly replacing our blood. Red blood cells have a life span of around 120 days. When you give a transfusion, those cells are already old. They will die off and be replaced by your own new blood cells with time. So even if there was a very subtle mismatch with the donated blood that might result in slightly faster killing of the donor blood, it wouldn’t matter because the cells die off and get replaced anyway.

If you think about a heart transplant or another organ, that organ needs to last the rest of your life. So a very slightly mismatch, and very low level attack over time is far more important. Slow sustained attack from the immune system damages the organ and reduces the length of time it will work. So get the match as close as possible to start with and then suppress the immune attack more, and the transplant will last longer

The ideal situation for a transplant in most cases would be an identical twin. The ID badges match perfectly and no immunosuppressive would be needed.

Ask more questions because I’m not sure my ID badge idea works well

Anonymous 0 Comments

Organs are really big and scary to your body! Blood isn’t that scary so your body thinks it’s okay 😀

Anonymous 0 Comments

I don’t know I donate blood all the time but when I think about receiving someone’s blood makes my skin itchy on the inside.

Anonymous 0 Comments

Finally my years of training as a carbohydrate chemist come into play!

Basically, your cells all have a number of small but complex sugar chains on their surface. Your body learns early in development to recognize this pattern to be “self” and anything else to be “other” which needs to be removed. On blood cells, specifically red blood cells, there is a much more limited diversity of sugar chains, which give rise to the blood groups most people are familiar with. But on other tissues the structures are more complex. Basically, it much easier to trick your body into thinking blood is “self” than for a complete organ.

Anonymous 0 Comments

People are talking about A,B,O antigens and red blood cells not having a nucleus, but that’s not the main reason.

The single most important factor for organ rejection is MHC-1 (this is the thing that’s being tested when you test if you’re a match for organ donation). Red blood cells don’t express it.

Slower rejection based on more subtle mismatches don’t really matter because you don’t need the donor cells to survive long term anyway.

Anonymous 0 Comments

Blood is pretty simple. It can have one or two markers, or none at all. There is another identification marker it can either have or not have.

If your body does not have blood markers, it is afraid of any marked blood and almost certainly will treat that as a invasion. If you have all the markers then your body is less likely to react to anybody’s blood.

But for meat it’s a whole different story. Your body doesn’t know if you received a replacement kidney from a stranger, or if you have a parasite in your body that already ate one of your kidneys. Your immune system goes around sniffing cells trying to identify if it is “you” or “not you” and as a organ recipient you need to use immunosuppressants to limit your body’s ability to identify a foreign organ, while keeping it strong enough to identify life threatening infections.

Every cell in your body contains your DNA. A strangers organ does not contain your DNA. Your body is able to identify that a large mass of not you is inside of you, and understandably it freaks out.

Anonymous 0 Comments

To put it very simple:

Your body has an immune system designed to attack anything that it doesn’t recognize as you.

This is useful when dealing with foreign invaders such as viruses, bacteria and even bigger things like worms and also your own cells if they look like they may be in danger of being becoming a cancer.

Your immune system will attack anything that doesn’t look like it belongs in your body.

This is a very useful feature and will keep you alive normally.

Occasionally it may get overenthusiastic and overdo things and attack healthy cells and you get one of those weird autoimmun diseases like Lupus.

There is also some very clever stuff build in to not attack foreign living things on the rare occasions when we want them to grow in a human body like pregnancy and to a lesser degree you helpful gut bacteria. This only rarely goes horribly wrong.

What our immune system is not designed at all to deal with it having a foreign organ transplanted into a body. Evolution has not at all prepared our biology for such Frankenstein stuff.

Not knowing any better your immune system will simply recognize what it find as a foreign invader and attack.

The immune system is not designed to recognize the foreign organ as anything other that a threat and will attack like it would attack a parasite it finds in your body.

The trick is to make it less recognizable foreign by taking an organ of someone who is either closely related to you or who just happens to be very similar to you by chance. You will still need to take meds that make the immune system less likely to attack anything at all.

Blood is easier than most other stuff because there isn’t really much variety.

There are only a very small number of different combinations of markers in your blood that might reveal it as foreign. This means that many people will share either the same set of markers as you or have one that is compatible.

If you are O- you can donate blood to everyone and it will be accepted but only receive blood from another O- person. If you are AB+ you can only donate to other AB+ persons and have everyone else reject your blood but receive blood from everyone.

There simply are too few combinations for everyone to be completely incompatible with everyone else but also there are enough combinations that transfusing blood at random can be like Russian roulette with an unknown number of bullets in the drum.

We could probably have evolved a much greater variety of blood types but that could pose a problems during pregnancy/birth when you want to avoid immune system overreacting about someone else’s blood.