From Longman Dictionary of Contemporary Englishimmune systemimˈmune ˌsystem noun [countable] Mthe system by which your body protects itself against disease My immune system is not as strong as it ought to be.
Examples from the Corpus
immune system• Now they know a two-pronged approach is needed: blocking the virus and rebuilding the damaged immune system.• One big problem may be the human immune system.• Might not that message been taken up by my immune system?• The site of the original interaction between antigen and the immune system presumably determines the distribution of the granulomatous inflammation seen.• Within several months of initial infection, however, the immune system mounts a more effective response.• This hormone helps to control growth of muscle, bone and the cells of the immune system.• These cells form part of the immune system and help to prevent the body from getting diseases.• They are eager to try anything they hear will boost their immune system, vitality and libido. 