If most organ cells, like in the liver, are replaced every three years or so, why isn’t a transplant eventually accepted by the new body?

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If most organ cells, like in the liver, are replaced every three years or so, why isn’t a transplant eventually accepted by the new body?

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Anonymous 0 Comments

what exactly are you replacing?

if the original liver had to be removed for a transplant, the new organ is not using the former’s hepatocytes(liver’s precursor cells) because they are not present anymore.

whatever replacement these cells do is gonna be based on the donor’s cells.

Anonymous 0 Comments

First, that 3 year rule is basically nonsense. Cell turnover varies substantially between organs, tissues, and cell types. Second, the transplanted organ produces proteins that the host immune system identifies as foreign and attacks. Sure, the cells in the transplanted organ will divide and expand, but all the cells that are derived from the transplant contain the same incompatible proteins and will continue to be identified as foreign.

Anonymous 0 Comments

Let’s take a liver as an example. Each cell contains a string of DNA that acts as a recipe for various proteins. These proteins are what the host body sees as foreign and attacs, because it is produced from another DNA recipe.

When a cell “reproduces” it splits in two, each one keeping a copy if the original DNA. In effect the liver will keep the donor DNA for ever.

Anonymous 0 Comments

All cells that contain a nucleus have a Major Histocompatibilty Complex (MHC). This MHC is used to help your immune system recognize friendly cells (aka host cells) as well as a couple other things. When a transplant occurs, those donor cells contain the donor MHC as well. MHCs are more unique than fingerprints, so the odds of having an MHC similar enough to the host MHC so as not to trigger the immune system is… very unlikely.

There are mainly three possibilities with most transplants: hyper acute rejection, acute rejection, and chronic rejecting. The ideal transplant will be chronically rejected, meaning that the transplant will take years to no longer be accepted by the body. This can be done using immunosuppressive medicines to stop the body from rejecting it via the other two possibilities; this of course leaves the host with a weakened immune system and a life long prescription of immunosuppressants.

Source: made a B in Immunology

Anonymous 0 Comments

Because the replacement cells are still made by the donor organ.

The problem with transplants is that host’s immune system recognizes them as foreign and wants to attack them. If Alice received a kidney from Bob, Alice’s immune system recognizes the cells in Bob’s kidney as not-Alice. When Bob’s kidney’s cells get replaced over time, it’s Bob’s kidney that’s doing the replacement. So all the new cells have “Bob” written all over them, and not “Alice”, because they were built based on Bob’s blueprints (DNA) and not Alice’s.

Anonymous 0 Comments

Any replaced cells in a transplant organ are made by the foreign organ, not your own body. So they are just as rejectable as the original cells.

[I hadn’t ever heard the 3-year thing before, but even assuming it is true, it doesn’t really help at all here for the reason I just stated.]

Anonymous 0 Comments

DNA are the “building blocks of life.” DNA lay out a series of instructions or “blueprints” to how we are made. No two human beings alive, even identical twins, have the same DNA. “Cells” are the smallest piece of life, making up living beings. That liver transplant makes up cells from another person whose DNA was not the recipient. Our bodies are smart enough to realize this. Our body attacks any new liver as a foreign element. To avoid this, you are put on medicine for the remainder of your life to suppress your body’s ability to do this. This also weakens you against sickness and disease.

Anonymous 0 Comments

Outsider cells are replaced by more outsider cells.

The new organ’s own cells are the ones training their replacements, so to speak.

Anonymous 0 Comments

My cells have my unique DNA that’s a combo from my mom and dad. Your cells have your unique DNA that’s a combo from your mom and dad.

Let’s say we want to transplant your liver into my body. Your liver is made up of your cells, and your DNA. My body is made up of my cells and my DNA. If we stick your liver in my body, my body will think your DNA is a foreign invader, and will attack.

It’s not exactly the same concept, but a good analogy would be thinking about why our body responds to a bacterial/viral infection. Our body recognizes that the bacteria/virus is “foreign” because the genetic material is different than the DNA in our own cells, and activates the immune system to attack these invaders. Similarly, my body will recognize that your cells are “foreign” because it’s not the same DNA, and will activate the immune system.

As an aside, this is why we want organs donors to be a “match”. The closer the donor matches the recipient, the less likely the recipient’s immune system will think the organ is an invader, which means the organ is less likely to get rejected.

Also, idk where you got the 3 year cell turnover rule, but that’s not really accurate. Certain cells (for example, the heart and brain), essentially never regenerate. This is why heart attacks and strokes are bad—those cells are dead and can’t come back. Meanwhile, skin cells and cells in our intestines regenerate pretty rapidly.

Anonymous 0 Comments

Replaced is a bit of a misnomer. A million cells in your body die every second. The “replacement” cells are generated through mitosis, where a cell duplicates its DNA and separates itself in to 2 cells. So your body produces new cells from the previous existing cells, all containing your DNA. A transplanted organ does the same thing. Its cells duplicate their DNA and split in to 2 cells. The transplant continues to have its DNA, separate from your own, in perpetuity. Thus it will always be seen as a foreign object and won’t assimilate to your body.