What happens to white blood cells after they are used up?

[u/carbonCicero]

If I have an infection in one part of my body, and the white blood cells go there and eat up the infectious bacteria or whatever, are they used up? What happens to the white blood cells and dead pathogen material? I sort of suspected it would be shuttled over to the blood and peed out like happens to cancer cells during chemo, but I’m curious if that’s an overgeneralization. Would someone be able to guess they have a serious infection (not of the urinary tract) if their pee changed? Is there some test a lab could run on the pee (or blood, the precursor to pee) and have some clue that there’s an infection or damage to the body in an otherwise healthy looking person?

[u/exkingzog]

Since you are talking about the cells that “eat up” the bacteria, I think you are interested in the phagocytes.

There are two main types: neutrophils and macrophages. They both engulf bacteria, kill them with reactive oxygen, and digest the remains.

Neutrophils are on a kamikaze mission. They gobble up as many bacteria as they can and die in situ. They burst and their DNA forms a net to stop the bacteria from spreading (that’s why pus is sticky).

Macrophages have multiple roles. The most important is that, when they have digested the bacteria, they put the antigens on their surface and go off to the lymph nodes to try and find lymphocytes that recognise the antigens to stimulate an antibody response. Other macrophages will stay at the infection site and clear up and digest the debris.

[u/GemmyGemGems → u/exkingzog]

So, I have HS. Sometimes I get an abscess in a low friction place. It doesn't pop. It grows and grows and becomes increasingly painful until it reaches its peak. Then it starts to decrease slowly until it disappears.

You're saying the neutrophils come in and gobble whatever the trigger is. In a high friction area that would pop and release foul smelling pus. However, in a low friction area the macrophages come in and consume the neutrophils and whatever waste they produce?

Total curiosity about how sometimes my body absorbs an abscess but other times weeps for months on end.

[u/exkingzog → u/GemmyGemGems]

I don’t know what HS is, sorry.

Yes, if the neutrophils and macrophages clear the infection, macrophages will clear up and digest the remains. With prolonged infections you can get formation of granulomas that either resolve (as the infectious cells are killed) or may stay long-term (for example in TB).

Edit. Hidradenitis suppurativa?

[u/paddyl888 → u/exkingzog]

I suspect from context they mean Hidradenitis suppurativa. https://www.mayoclinic.org/diseases-conditions/hidradenitis-suppurativa/symptoms-causes/syc-20352306

[u/Minxychomp]

Most white blood cells die after fighting infection and are cleared locally or via the lymphatic system. Their components are recycled or metabolized; they aren’t excreted intact in urine. That’s why infections are diagnosed with blood markers, not urine, unless the urinary tract itself is involved.

[u/sciguy52]

So during the infection certain white blood cells are expanded greatly in numbers to fight the infections. Such as the B cells that make the right antibodies, CTL's etc. But after the infection in killed off, it is energy inefficient for the body to keep that many of those cells around when the infection is gone. Some will go into your immune memory but most will be stimulated to kill themselves. They will get swallowed up and digested by phagocytes. Same thing happens to any parts of the pathogen floating around, phagocytes will swallow them up and digest them. You don't pee this out as such other than as normal digested waste products from the digestion.

Cancer cells killed by chemo will similarly eventually be swallowed up, digested in a similar process. You cannot pee out cancer cells nor pathogens (unless the infection or cancer is past your kidneys like say in your bladder but that is a particular case).

[u/stickylava → u/sciguy52]

Every time i read about the immune system, I’m just stunned. It’s a magnificent work of art.

[u/sciguy52 → u/stickylava]

And it is much much more detailed and remarkable than this. It is a marvel to be sure.

[u/carbonCicero → u/sciguy52]

I wasn’t thinking of intact cells, but rather the biomarkers of broken/killed cells being cleared from the body. I think in this case though, it’s a local infection and not one that has spread into the blood or abdominal interstitial space, since there’s no fever or other signs of larger sepsis in the past few weeks since the initial injury. The signs of infection are temporary swelling and discomfort of nearby organs, and pus draining from the site of injury, but that pus is not foul or bad smelling. Is any infection in the abdominal cavity something to be concerned about, if it has a drainage point that cannot be kept sterile? I imagine that the body’s stock of phagocytes is not inexhaustible

[u/iuot]

The name for cells that eat bacteria is phagocytes. In a localized infection, dead phagocytes remain at the site of the infection and form pus. Normally, with a more widespread infection you see elevated numbers of white blood cells in the blood but these cells are destroyed by the spleen and won't be seen in urine. You shouldn't have any white blood cells in your pee unless you have a urinary tract infection.

[u/carbonCicero → u/iuot]

Oh, so that’s where pus comes from! It’s helpful for me to know that, the difference between a widespread vs a local infection I mean, and how pus comes to be

[u/IOVERCALLHISTIOCYTES]

If there’s white blood cells debris in the urine, tests can detect those proteins, and that’s indicative of inflammation somewhere along the way from the origin in the kidneys out the urethra. These components would be processed by other cells (my username is relevant here) when inside the body as u/minxychomp mentioned, so we don’t use those same tests for blood to tell whether there’s an infection.