The immune system plays an essential role in safeguarding health by expertly navigating three fundamental challenges: implementing universal responses to varied threats, establishing tolerance for the body's cells to avoid autoimmune disorders, and maintaining appropriate reactions to threats to prevent overreaction or underreaction. Future discussions will delve into these challenges in detail.

Autoimmunity refers to the immune system mistakenly attacking the body's tissues and cells due to a breakdown in self-tolerance, often causing chronic inflammation and diseases like rheumatoid arthritis and multiple sclerosis. Immunodeficiencies, on the other hand, are characterized by a compromised immune system increasing susceptibility to infections, which can be congenital or acquired through factors like infections and certain medications.

The immune system's responses are influenced by demographic factors like age, sex, genetics, ethnicity, nutritional status, socioeconomic status, environment, medical history, lifestyle, stress levels, and exposure history. These factors account for variances in susceptibility to infections, vaccine responses, and immune-related disorders. Understanding these variables is vital for personalizing healthcare strategies and public health efforts.