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tinybabymoose t1_iuhswx8 wrote

This is not going to be a compete answer but there’s several processes involved. First for the WBCs to get to the right area of tissue in the body, the blood vessel wall cells start expressing “selectins” which start to slow the WBCs down, then the WBCs bind and cross through the vessel wall using integrins and Cell adhesion molecules. Also there are macrophages and dendritic cells which when they encounter a pathogen release “chemokines” which create a concentration gradient for the WBCs to follow. Once close enough to the bacteria, neutrophils particularly are able to follow bacteria in the same way, following the concentration gradient of products the bacteria is releasing. (I can’t remember which chemical they follow but I think it may be ammonia?)

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Xambia t1_iuhtjma wrote

Once the neutrophils make it to the bacteria they follow chemoattractants released from the bacteria (and behave as you see in the video) usually in response to oligopeptides released from the bacteria which have a formyl functional group attached to the N-terminus of the peptide (ex: fMLP)

Edit: I should add that these oligopeptides bind to protein receptors (GPCRs) on the surface of the neutrophil and the location of these activated receptors on its surface let the neutrophil "know" where to go.

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_AlreadyTaken_ t1_iui3lim wrote

Some microorganisms, like malaria, are very good at hiding themselves and the immune system is blind to them.

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kippypapa t1_iuiq68j wrote

So why did these cells evolve this way? How did cells like this start out?

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Xambia t1_iuizjkj wrote

Are you asking "Why/how did white blood cells evolve chemotaxis?" or "Why/how did bacteria evolve to release chemoattractants?"

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CTH2004 t1_iujchrp wrote

well, I dunno bout him, but I'm curious about both!

and, basicly they "smell" bacteria, right?

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Limmert t1_iujwe7i wrote

They don’t «smell» it like we think of the word «smell». It’s more like: pieces (chemoattractants) fall of the bacteria and attaches to receptor on phagocyte (because high consentration of a substance = higher chance of said substance to «collide» with the receptor on the phagocyte).

And when a «piece» binds to the receptor it causes an intracellular signal in said phagocyte -> phagocyte shoots out lamellipodium (which basically is a grappler that binds to the ecm in the direction of the receptor binding, and contracts pulling the phagocyte in that direction) -> repeat until catching your target.

I don’t know if that made any sense? Or if it was an answer to your question? The evolution is rather uncertain i believe.

Edit: Fagocyte -> phagocyte

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CindyTheHooker t1_iujxurs wrote

Did you mean ‘Phagocyte’ instead of ‘Fagocyte’? Fagocyte gave me an interesting definition…

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Enocli OP t1_iui2dmm wrote

Thank you!

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bawki t1_iuj4nho wrote

Also the majority of WBC kind of "roll" along the blood vessel walls, which is a process corticosteroid therapy can disrupt. This will manifest as initial pseudo leukocytosis as it frees leukocytes from the blood vessel walls and therefore increase blood concentration for leukocytes.

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tr14l t1_iui0h34 wrote

So, basically, it's not that the WBCs are following the target, but rather they are getting pushed toward it?

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fujiko_chan t1_iui8wrx wrote

Not quite. I know this isn't ELI5, but basically if the WBCs are policemen, the selectins (and others) on/near the vessel wall are going, "Hey, my friend is in trouble! This way!" and pulling on their shirt sleeves. Once it exits the vessel, they can follow concentration gradients.

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AruthaPete t1_iuiidm8 wrote

And following the bacteria from them is a bit like following the exhaust fumes of a get away vehicle faster than the vehicle is moving.

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InviolableAnimal t1_iuj6f0h wrote

No, it's more like they follow the bacteria by smell (detecting its chemical traces, and also the communication "scents" of other WBCs) rather than "sight".

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Moonandserpent t1_iuj1yht wrote

Nice! My "educated" guess answer was something like "chemical breadcrumbs," good to see I'm at least partially correct!

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Themacuser751 t1_iuj5utg wrote

So part of it is that the bacteria leaves a trail that the WBCs can follow?

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amakai t1_iujibn6 wrote

Is it possible for a bacteria not to release any chemical, at least temporarily, to "erase the trail" and hide itself from immune system?

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Guysmilez t1_iui8opm wrote

Really? You can’t name the chemical the bacteria is releasing?

Jk thanks for the explanation

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