Overview of the Immune System
The immune system protects the body against infection and disease. It is a complex and integrated system of cells, tissues, and organs that has specialized roles in defending against foreign substances and pathogenic microorganisms, including bacteria, viruses, and fungi. The immune system also functions to guard against the development of cancer. For these actions, the immune system must recognize foreign invaders, as well as abnormal cells and distinguish them from self (1). However, the immune system is a double-edged sword in that host tissues can be damaged in the process of combating and destroying invading pathogens. A key component of the immediate immune response is inflammation, which can cause damage to host tissues, although the damage is usually not significant (2). Inflammation is discussed in a separate article; this article focuses on nutrition and immunity.