OBJECTIVE: We evaluated mannose binding lectin (MBL) protein production and histological localization, MBL2 gene expression and genotypes distribution in patients characterized by recurrent tonsillitis, with the aim of verifying the innate immune response to the infection and inflammation occurring in the tonsils. METHODS: MBL2 exon 1 and promoter polymorphims were detected by PCR amplification and subsequent direct sequencing of the amplicons. Monoclonal antibodies to MBL were used on frozen sections of tonsils for the immunohistochemical localization of MBL protein. MBL Oligomer ELISA kit was used to quantify the level of MBL in the serum of the 30 patients with recurrent tonsillitis. Quantitative RT PCR for the evaluation of MBL2 expression of MBL high producers (HP), low producers (LP) and deficient producers (DP) was performed using the Hs00175093 gene-expression Assay on Demand. RESULTS: The distribution of the MBL2 combined genotypes was as follows: 21 HP (70%; 15 HYA/HYA, 6 HYA/LXA), 6 LP (20%; 5 HYA/0, 1 LXA/LXA) and 3 DP (10%, all 0/0). MBL levels were directly correlated to the MBL2 combined genotypes: HP patients showed higher mean MBL concentration of 4044 ng/mL, LP patients were characterized by a mean of 905 ng/mL whereas those with DP combined genotype presented extremely low levels of MBL (mean value of 74 ng/mL) (p=0.0005). Immunohistochemistry performed on tonsils sections demonstrated that MBL was widely distributed throughout the surface of the basal lamina of all the 21 HP subjects. MBL was undetectable in situ in both LP and DP patients. MBL2 expression, although at very low levels, was found for the HP group, the LP and the DP group as well. CONCLUSIONS: We confirmed the genotype-phenotype correlation of MBL2 gene exon 1 and promoter polymorphisms with the quantitative production of serum MBL, we reported a very low MBL2 expression at local level in tonsils and we determined the in situ localization of MBL in the basal lamina of the tonsils of patients who underwent to tonsillectomy. Our findings suggest an important role of MBL protein in the innate immune response of the tonsil to pathogens, as in recurrent infection and inflammation.