Tonsil-related skin diseases and possible involvement of T cell co-stimulation in chronic focal infection.

Some inflammatory skin diseases are known to be related to tonsil focal infection at their onset. Administration of antibiotics is adequate treatment in most acute or subacute cases. However, chronic focal infections in the tonsils could cause chronic skin diseases like pustulosis palmaris et plantaris (PPP), and it is our frequent experience that tonsillectomy leads to a dramatic and persistent improvement of PPP skin lesions. The expression of inducible co-stimulator (ICOS), a co-stimulatory receptor on activated T cells, was significantly higher in tonsil tissues from PPP patients than in tonsil tissues from non-PPP patients. Moreover, ICOS expression in tonsil tissues from 3 patients with psoriasis vulgaris that was strongly suspected to be related to tonsil focal infection was also high, suggesting that the activation of T cells via ICOS costimulation in focal infections likely triggers inflammation associated with tonsil-related skin diseases. PPP is notable today for paradoxically induced skin lesions in patients treated with TNF-α antagonists for rheumatoid arthritis, Crohn's disease, psoriasis and psoriatic arthritis. It is important to clarify the immunological milieu in PPP not only for the treatment approach but also for understanding these unexpected reactions.