This review comments on basic and clinical immunology articles that were published in 2005, with a focus on those that appeared in the Journal of Allergy and Clinical Immunology. In the area of basic immunology, mechanisms of the innate immune system and its interaction with the adaptive immune system were described, with special consideration to applications in biodefense strategies. T regulatory cells were further characterized in their role for the control of allergic, autoimmune, and neoplastic disorders. The function of the thymus Hassall’s corpuscles was reported to be the generation of T regulatory cells. Flavonoid molecules obtained from medicinal herbs, including astilbin and epigallocatechin gallate, were discovered to have immunomodulatory properties. Advances in clinical immunology resulted from efforts to develop a newborn screening test for severe combined immunodeficiency and the elucidation of the crystal structure of the IL-2 receptor γ chain. Mutations in the membrane receptor transmembrane activator and calcium modulator and cyclophilin ligand interactor were found in patients with common variable immunodeficiency. New therapeutic options are described, such as the use of infliximab for granulomas and GM-CSF for chronic ulcers in patients with common variable immunodeficiency. The importance of mucosal immunity in acute HIV infection is cited, as is the role of CD8⁺ T-cell activation in HIV disease progression in children.