National Cancer Institute: "Immunotherapy: "Using the Immune System to Treat Cancer."<br>AARP: "Super healing."<br>U.S. National Library of Medicine: "Common Colds: Overview."<br>U.S. National Library of Medicine: "How does the immune system work?"<br>National Institute of Diabetes and Digestive and Kidney Diseases: "Ulcerative colitis: What is ulcerative colitis?"<br>Mayo Clinic: "Ulcerative colitis."