Realistically, it's very unlikely we'd have compatible chemistry for them. It's like, our bacteria would be hopeless against ammonia blood or something. But f

Realistically, it's very unlikely we'd have compatible chemistry for them. It's like, our bacteria would be hopeless against ammonia blood or something. But fungi/protozoa are probably a better analogy... they're more generalists and would stand a better chance of being invaders. Against something totally alien, if it could survive or thrive in an animal, I'm skeptical our immune system would be worth much, but I don't know.