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Comment by water8 | Hacker News Reader

Isnt that what a T-cell does?

IDK why some smartasses, who probably have not taken Biology in HS, decided to bury your comment but some subtypes of T cells are indeed able to attack virus-infected cells.

https://en.wikipedia.org/wiki/T_cell

I think "attacking" and "relying on for nutrition" isn't the hardest distinction to make. You wouldn't call a Ukrainian tank a "Russovore", would you?

They "attack" them usually in the form of passing a message like "please destroy yourself".

I've been wondering recently, and probably naively, about a related question: does the human immune system have any kind of metabolic (digetsive) function? My understanding carries to the various ways that immune cells destroy non-self cells through processes like phagocytosis and lysis, and to the mechanisms for excreting waste products via, e.g., lymph. It seems like there would be opportunities to recycle components from bacterial or other cells, similar to how Halteria appear to be "eating" viruses. But I haven't found any references to this in a cursory search of pubmed (maybe because I just don't know the right keywords).

So my question for HN: do immune cells "digest" their prey?

At least some of them do, particularly macrophages. https://en.wikipedia.org/wiki/Macrophage

OP conflated digestion and metabolisis. Although macrophages 'digest' in that they break things they 'eat' into component parts, they do not use those parts for energy (metabolisis). This is the key novelty here, these virovores are metabolising the viruses (i.e.: using them as an energy source), rather than just breaking them down.

Food is essentially just a bunch of molecules/chemicals. Digestion is essentially a word for breaking big complex chemicals (ie food) down into smaller simpler chemicals. And metabolism is just a word for any chemical process which takes food, digests it, and yields energy and/or raw materials to synthesize and sustain life functions.

All cells, including those which make up the immune system, need energy to function, and material to grow, and thus require a metabolism to sustain themselves.

As for whether immune cells "digest" their prey (meaning break them apart), the answer is yes. Neutrophils are known to ingest (eat) all sorts of pathogens, and are known to digest bacteria and fungi. I'm not so sure with viruses, as they are much smaller entities, but there are probably certain cellular circumstances in which they are also "digested". If you are wondering whether they are also utilized for energy/material upon digestion (ie "metabolized"), that is more complicated to say for sure, but the answer is likely yes under certain circumstances, and depending on a lot of things.

Thats because, cells metabolize energy in a lot of different ways. In fact, there are so many ways cells "metabolize", there are probably thousands of "metabolic pathways" [1]. And when you really dig deep into it; proteins, enzymes, viruses, cells, and even us, look to be nothing other than complicated molecular machines [2], just different in scale and complexity.

[1] - https://en.wikipedia.org/wiki/Metabolic_pathway

[2] - https://en.wikipedia.org/wiki/Molecular_machine

Neutrophils for example take up their "prey" in vacuoles and then merge those vacuoles with vesicles containing acid.

In some form there is a "digestion" happening. It's actually a non-trivial question to say if there is any form of energy that "escapes", for example in the form of keto-bodies, lipids, whatever, but it's certainly not very significant and certainly not the point of the digestion.

No, not really. T-Cells don't "eat" stuff. You may mean macrophages, neutrophils and so on. And those actually get their energy mainly from glucose, while they actually expend energy to destroy the stuff they take up.

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