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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 |