Background: Recurrent acute tonsillitis is one of the most frequent ENT referrals, yet its pathogenesis remains poorly understood, and tonsillectomy still costs the National Health Service more than £60 000 000 annually. Antimicrobial cationic peptides are components of the innate immune system. They are generally small, highly positively charged peptides with broad spectrum antimicrobial activity which function as the body's ‘natural antibiotics'. The role of antimicrobial cationic peptides in the susceptibility of patients to recurrent acute tonsillitis is unknown.

Aims: To characterise and compare antimicrobial cationic peptide expression and localisation in human palatine tonsils from control subjects and recurrent acute tonsillitis patients, and to assess the potential role of these peptides in the pathogenesis of tonsillitis.

Methods: Palatine tonsils were harvested with informed consent from 19 recurrent acute tonsillitis patients and from five control subjects undergoing tonsillectomy for sleep disorders. Total ribonucleic acid was isolated and antimicrobial cationic peptide expression was characterised using reverse transcription polymerase chain reaction. Fluorescent immunohistochemical techniques were used to localise antimicrobial cationic peptides within fresh frozen tonsil sections.

Results: Using molecular analyses, the palatine tonsils from control and recurrent acute tonsillitis subjects were confirmed as a site of expression of the antimicrobial cationic peptides human β-defensin 1–3, LL-37 (cathelicidin) and Liver expressed antimicrobial peptide-1 (LEAP-1). We also demonstrated for the first time the expression of Liver expressed antimicrobial peptide-2 (LEAP-2). Our analyses indicated that all six antimicrobial cationic peptides were expressed in all 26 tonsil samples. Immunohistochemical staining indicated that the antimicrobial cationic peptides were localised to the tonsil surface and crypt epithelium. However, the surface epithelium of tonsils from recurrent acute tonsillitis patients showed reduced amounts of antimicrobial peptides human β-defensins 1 and 3, and LL-37, compared with healthy controls.

Conclusion: The tonsil epithelium synthesises an array of antimicrobial cationic peptides which function as host defence. Preliminary immunohistochemical data suggest that the surface epithelium of tonsils from recurrent acute tonsillitis patients contains reduced amounts of such peptides, which may increase these patients' susceptibility to infection.