White blood cells or leukocytes are known to fight invaders, infections or basically anything foreign. They also contain DNA (while red blood cells don't). But what about foreign "white blood cells" received in a transfusion or sexual intercourse (as semen, not sperm, holds "lymphocytes" which are a type of white blood cells, they can "possibly" enter the blood circulation, not quite sure).

Anyways, my question is:

1) Do white blood cells "fight" the foreign white blood cells and kill them off? OR is that something cleaned by the spleen itself? (considering WBC lifespan is 13-20 days so they die off their own). So do they "get" attacked by the host's WBC or do they naturally die off their own?

2) Does the body detect them as "foreign"?

3) I've also heard about the "extracellular DNA" phenomenon. Which is, the ability of DNA to exit a cell (while it's dying) and float in the extracellular (non-cellular) environment. The DNA is degraded during a cell death but it can definitely exit a cell and float non-cellular in the environment. This is also true for the cell's RNA. This is labelled as an "extraceullar DNA/RNA" or a DNA/RNA without a cell. So that being said, can the DNA of foreign leukocytes or white blood cells that do not belong to the host (having a completely different DNA, of course) exit it's cell during it's death and become extracellular DNA? Is that even remotely possible? Also, can that extracellular DNA (keep in mind, the DNA is a fairly stable molecule) ever remain in the circulation or the human body for life? Perhaps in the bloodstream? or in one of the organs? or in a biofilm? (considering exDNA is a component of a biofilm) Does that even have the "slightest" possibiliy of happening? For it to remain there for life?

1) If it is, wouldn't the body (the immune system or WBC) ever "react" or "act" on eliminating the "foreign DNA" of another person that's floating around? Or is that something which will remain for life OR be eventually faded away? I'm well aware of enzymes such as DNAses/RNAses (enzymes responsible for DNA and RNA degradation) but do they do that in the blood? And that being said, "sometimes" in a biolfilm they don't.

2) And even if it gets stuck in a "biofilm" (assuming it's possible?), would it "EVER" degrade eventually or remain there for life? OR CAN/WILL the "biofilm" holding such extracellular components degrade eventually or will it remain for life as well? (can they remain there forever?).

3) A simple way to explain this would be if I insert hundreds of "foreign DNA" (strands, not cells) into your blood stream, what would happen to them?

4) Can it get "stuck" or get glued to an organ or it's cells and remain there for life somewhere out in the deep where they won't be found? Since I'm not an expert in molecular biology I don't understand. In other words, can it EVER remain there for life with "ANY" slightest 1% possibility with all the possibilities I've explained or any other possibility of it remaining there for life? And same goes for the RNA. Having someone else's DNA and RNA scares the shit outta me. And having that for the rest of my life, makes me really uncomfortable.

My question is for both the DNA and the RNA.

I don't want "assumptions" or hypothesis please. Please answer if you're an expert in microbiology/molecular biology, others, etc. And are well aware of what I'm talking about. I will greatly appreciate it.

Also, this is a tricky one! (I completely don't understand this)

The molecules secreted by these "foreign" white blood cells after their death would provide structural and biochemical support to other cells so wouldn't a part of his trace (his molecules) would remain in other cells forever once they consume it? Or the molecules get replaced on a cellular level itself if I'm not mistaken? Wouldn't his molecules be a part of my body forever?

Please answer if you're an expert in microbiology/molecular biology, others, etc. And are well aware of what I'm talking about. I will greatly appreciate it. I don't want assumptions or hypothesis only whatever is known, proven, researched & concluded as a fact. :)

Thanks guys,


  • 2
    $\begingroup$ Please shorten your question body. Your question body has some unnecessary sentences. $\endgroup$ Jul 21, 2017 at 5:15
  • $\begingroup$ It might be good for getting answer of your question that you don't restrict the job to specialist in molecular biology. Most of the people are here not specialist, but they are enthusiast and can provide good answers. $\endgroup$ Jul 21, 2017 at 9:58

1 Answer 1


Okay, you have a lot of questions there. I'll try to give some answers, but if you want more details or background knowledge I'd recommend you to read /study more about immunology (none of your questions are actually about molecular biology or cell biology).

2) Foreign cells are generally recognised by the immune system, based on the HLA molecules on the cells: all cells that do not have the exact same HLA molcules are recognised as forgein and attack by the immune system (cells without HLA are not human and by 'default' foreign). Since there are many different variants of the HLA class I gene and humans have usually 6 different ones, its very unlikely that a cell from someone else would not be attacked (that's why it's so hard to find matching organ donors).

1) Foreign cells are attacked by the immune system, the spleen's purpose is to remove/recycle old blood cells from the body itself. Depending on how the immune system recognises a cell (e.g. by antibodies or diretcly by immune cells) different strategies to fight the foreign cell are activated.

3) There are certain receptors on some immune cells that can recognise extra-cellular DNA or RNA. This recognition is not sequence specific und usually causes an inflammatory reaction, because extra cellular DNA is a sign of either cell damage (by necrosis) or invading pathogens. After the immune system recognised such 'invading' factors they are usually taken up and removed by macrophages.

Generally speaking all of this only happens if foreign cells or DNA manages to get into your body (e.g. if you would inject it). It's very unlikely that DNA or cells can pass into your body unless you have open wounds. (White blood cells usually only are able to pass the endothelium of blood vessels, not other kind of barriers)


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