How neutrophils get out of blood vessels – it’s crazy!

First, a disclaimer: I won’t be testing you on the stuff in this post. I just want to show it to you because it’s so incredible! With that out of the way, let’s take a look at some neutrophil craziness.

In order for neutrophils to fight infection or help clean up after an injury, they need to get out of the blood and into the affected tissue. The name for this process is “recruitment,” and it consists of a series of five steps. Most of these steps are pretty straightforward, but one of them – diapedesis, or migration through the vessel wall – looks insanely difficult and painful. If neutrophils had nerves. Which they don’t. But still.

By the way, diapedesis comes from the Greek dia (through or across), the Latin ped (foot), and the Greek esis (a suffix used to form nouns of action or process). So diapedesis is the process of neutrophils poking their tiny feet through the blood vessel wall! OH MY GOSH that makes me so happy. 

Here’s an electron micrograph of a neutrophil undergoing diapedesis. Before you scroll down any further, take a good look at the photo. The neutrophil is the cell in the middle…and it’s sucking its gut in and squeezing between two endothelial cells. Can you figure out which side is the tissue side and which side is the interior of the blood vessel? There’s a labeled figure at the bottom of this post when you’re ready.

Here are the five steps:

  1. Margination. Neutrophils stick to the inside of the vessel walls.
  2. Rolling. This is what it sounds like: the neutrophils adhere briefly to the endothelium, detach, adhere again, detach, etc. in a rolling fashion until they find a good stopping point.
  3. Adhesion. Then the neutrophils stick firmly to the endothelium.
  4. Diapedesis. Here’s the craziness! The neutrophils have to squeeze between the endothelial cells to get out into tissues. This is just nuts, because neutrophils are MUCH MUCH larger than the tiny little gap between adjacent endothelial cells. So they really have to suck it in, and slowly squeeze themselves through (without rupturing their cell walls or anything inside, by the way). How the heck do they do this?? They are so totally committed to fighting those bacterial that they will literally squeeze themselves through a tiny gap to get out of the vessel and into the tissue. Impressive. 
  5. Migration. Once they’re on the other side, the neutrophils shake it off, and migrate through the tissue to the exact place they are needed.

I’m exhausted just thinking about it. Good job, little neutrophils!! 

Here’s the same EM with labels.

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