Involvement of innate immunity in the pathogenesis of intestinal Behcet's disease

The involvement of excessive T helper 1 (Th1) cell functions in the pathogenesis of Behcet's disease (BD) has been reported. We therefore studied Toll-like receptor (TLR)-expressing cells, which play important roles in innate immunity in patients with BD. Peripheral blood mononuclear cells (PBMC) of BD and healthy controls, and tissue specimens of intestinal BD and Crohn's disease (CD) were analysed for messenger RNA (mRNA) and protein expressions by reverse transcription-polymerase chain reaction and immunostaining respectively. PBMC of BD expressed TLR-2 and TLR-4 mRNA almost comparable with healthy controls. Intestinal lesions of BD expressed TLR-2 and TLR-4 mRNA consistently. In contrast, TLR-4 mRNA was expressed preferentially and TLR-2 mRNA was expressed less frequently in CD lesions. In intestinal samples of BD, TLR-2 and TLR-4 mRNA were detected in ileocaecal ulcer lesions, but not in unaffected sites of the same sample, indicating the association of the TLR expression with the disease manifestation of intestinal BD. TLR-2-expressing cells which were simultaneously cluster of distribution (CD)68-positive produced interleukin (IL)-12 in the lesions, indicating the participation of TLR-2-expressing cells in the Th1 skewed responses in vivo. As a possible ligand of TLR-2, in BD self-heat shock protein 60 was expressed in peripheral blood lymphocytes and intestinal tissues. Collectively, TLR-2-expressing cells as well as TLR-4-expressing cells accumulated in the intestinal lesions of BD. IL-12 produced by TLR-2-expressing cells may contribute to the induction of Th1-dominant immune responses in intestinal BD.