The immune system is the body’s natural defense system. This delicate network of cells, tissues, and organs synergistically help fight bacteria, viruses, parasites, and even fungi. Building a healthy immunity to these invaders helps to produce white blood cells and other chemicals and proteins that help defend and extinguish these foreign substances. The production of antibodies is a major function of the immune system. Immunity is essential to help fight harmful antigens and keep the body properly balanced.