WordNet sense 1 ((of persons) not exempt from an obligation or liability):

nonexempt

WordNet sense 2 ((often followed by `to') likely to be affected with):

nonresistant, unresistant, nonimmune

WordNet sense 3 ((often followed by `of' or `to') yielding readily to or capable of):

susceptible

WordNet sense 4 (worthy of or requiring responsibility or trust; or held accountable):

responsible

WordNet sense 5 (at risk of or subject to experiencing something usually unpleasant):

apt