unsusceptible vs immune

unsusceptible is not a noun while immune is a noun.

Word	Noun	Adjective	Verb	Adverb
unsusceptible	No	Yes	No	No
immune	Yes	Yes	No	No

unsusceptible (noun)	immune (noun)
	a person who is immune to a particular infection

unsusceptible (adjective)	immune (adjective)
not susceptible to	relating to the condition of immunity
	secure against
	(usually followed by `to') not affected by a given influence
	relating to or conferring immunity (to disease or infection)