noun
Medical/biological term for the body's defense system against pathogens.
免疫機構が正常に働かないと、病気にかかりやすくなる。
If the immune system does not function properly, one becomes more susceptible to illness.
免疫 means 'immunity' in a broader sense, while 免疫機構 specifically refers to the immune system as a mechanism.
Compound of 免疫 (immunity) and 機構 (mechanism, system).