Studies of Tonsils in Basic and Clinical Perspectives: From the Past to the Future

The tonsils are located at the entrance of the pharynx as a cardinal constituent of Waldeyer's ring, taking part not only in local immune responses, but also in systemic immunity. Functional deficits of tonsils primarily underlie the pathogenesis of various characteristic disorders, including tonsillar focal infections such as palmoplantar pustulosis and IgA nephropathy, in addition to the highly prevalent sleep disorder called obstructive sleep apnea syndrome. Although the mechanisms underlying these disorders remain unknown, the tonsils have long been postulated as a unique and enigmatic immune organ. Lymphoid cells and tissues from surgically resected tonsils are often employed to analyze the human immune response from a retrospective view. This approach has provided much new fundamental evidence for understanding innate and acquired immune responses, thereby facilitating further studies in the fields of mucosal immunity and specific humoral immunity originating in the germinal center. Future studies of the tonsils in basic and clinical research are expected to reveal the mechanisms of tonsil-related disorders as well as the nature of human immunity. In this review, which is primarily based on our original research over the past 3 decades, we summarize our findings and discuss the future prospects of studies focusing on the tonsils.