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Major New Function Discovered For the Spleen
circletimessquare writes "The spleen doesn't get much respect — as one researcher put it, 'the spleen lacks the gravitas of neighboring organs.' Those undergoing a splenectomy seem to be able to carry on without any consequences. However, some studies have suggested an enhanced risk of early death for those who have undergone splenectomies. Now researchers have discovered why: the spleen apparently serves as a vast reservoir for monocytes, the largest of the white blood cells, the wrecking crew of the immune system. After major trauma, such as a heart attack, the monocytes are disgorged into the blood stream and immediately get to work repairing the damage. '"The parallel in military terms is a standing army," said Matthias Nahrendorf, an author of the report. "You don't want to have to recruit an entire fighting force from the ground up every time you need it."'"
It will be interesting to see if this holds true in humans. Lots of animals have spleens that seem more functional than ours. Cats and dogs, for example, can "transfuse" themselves with the blood from their spleen in response to bleeding, but this does not hold true for humans.
I'm sure someone cut open a spleen before and looked at it through a microscope. Wouldn't you see an unusually high concentration of the monocytes?
For one thing, compared to what? As the article points out
Its such a vascularized organ, and the risk of big-time hemorrhaging is so great, that if the spleen ruptures, itâ(TM)s a surgical emergency,â said James N. George, a hematologist with the University of Oklahoma Health Sciences Center.
It's full of blood, if you thought you noticed a high amount of monocytes, you'd probably think: they're blood cells and the spleen is full of blood cells. The finding is, as I understand it, that BLOOD from the spleen is higher in monocytes. You'd have to compare blood from the spleen to blood circulating in other organs.
The other issue is that monocytes would be hard to specifically identify, and probably impossible to count in tissue slices. This page has some examples of what monocytes look like when they're specifically stained (with hematoxylin and eosin I think), and what other blood cells look like. That's when they're stained just right and drawn out of an organ. If you're looking at slices of a spleen under a microscope, that's not going to jump out at you even if you were staining with H&E. The article used antibodies to specifically identify only monocytes. Antibodies recognize and can label specific proteins, they chose proteins that would be specific to monocytes. That's not something you do unless you're looking for monocytes specifically.
So you wouldn't notice monocytes unless you stained with antibodies specific to them, and even then, you wouldn't be able to compare them accurately in microscope sections.
In the real article, the authors seem to have used fluorescence-activated cell sorting (FACS) on spleen isolated blood to compare to circulating blood from other organs.
FACS as I understand it (never done it myself, only heard about, and I'm not reading the real article too closely either) is where isolated cells one at a time are sprayed through a laser. If the cell has a fluroescent tag on it, that makes it deviate from the path it would take if it doesn't. You can collect cells that deviate and cells that don't, the machine counts them, and you can then compare the ratios (easier than counting in a microscope.) So they were able to use that to show it had a higher ratio.
Collecting blood from isolated tissues, prepping it with the antibodies for monocytes, prepping that for FACS and then actually doing FACS is not trivial, you're not going to be doing it unless you're specifically testing a hypothesis like the ones the authors had.
(disclaimer: I'm not an expert in spleens, immunology, or FACS and I didn't read either article in depth.)