immune vs unsusceptible

immune is a noun but unsusceptible is not a noun.

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

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

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