The most practical and clinical reasons for attempting to understand the immunology of infections and disease revolves around the CD137 and CD137/41BB receptor and ligand molecules. This book covers all aspects of CD137/4-1BB pathway research from microbiology, infectious disease, molecular biology, biochemistry, and genetics to immune responses and potential applications in the diagnosis and treatment of human diseases. This pathway is emerging as one of the most important targets for manipulation of immune responses for disease diagnosis and treatment. This book is written by the man who discovered the CD-137 and B7H1 molecules in 1999.