Mast Cell Distribution and TLR4 Expression in Rat Tongue Epithelia

Mast cells are preferentially distributed within the microvascular endothelium in oral mucosa and play a protective role in host defense against bacteria. Toll-like receptors (TLRs) are a family of pattern recognition receptors that are critical for cellular response to a variety of bacterial, viral, and fungal products. Recent reports have demonstrated that TLR4 is closely linked with LPS signaling and that LPS activates mast cells to produce cytokines without degranulation.

Objectives: In order to examine role of TLR4 in mast cells, the distribution of mast cells and the expression of TLR4 in tongue epithelia were immunohistochemically analyzed in the present study.

Methods: Frozen sections of rat tongue were mounted on silane-coated glass slides and air-dried. The sections were then fixed, and treated with 0.3% H2O2 in PBS. Then, goat polyclonal IgG anti-TLR2, anti-TLR4 antibody (1:100) or PBS as a negative control was added. The primary antibody was detected with biotinylated goat anti-mouse IgG. Subsequently, sections were stained in parallel using the Labeled Strept avidin-biotin (LSAB) method, and the reaction was visualized by diaminobenzidine (DAB). Stained slides were then couterstained with Mayer's hematoxylin. Mast cells were observed with methyl blue staining.

Results: Expression of TLR4 was observed in mast cells located in the lamina propria of rat tongue. In the muscle layer, pervascular tissue mast cells were strongly stained positive for the TLR4. No apparent positive staining for TLR2 was observed in tongue mast cells.

Conclusion: These findings suggest that mast cells are present in TLR4 and may play an important role in host defense in tongue epithelia.