antigens « Back to Glossary IndexAntigens are molecules that the immune system reacts to. Related Articles: 14 – 4 Pathogenic outcomes15 – 2 Important Introductory Concepts of the Immune System15 – 4 The Immune System Is a Complex Collection of Organs, Tissues, and Cells15 – 6 Inflammation and the systems that react to it16 – 2 Adaptive Immunity – introductory concepts« Back to Glossary Index