 ([Figure. 0](#pone-0000000-g000){ref-type="fig"}).  ![Mean value comparison of subepithelial and deep tryptase positive mast cells in healthy controls, different stages of OSF, and OSCC.](pone.0000000.g000){#pone-0000000-g000}  Deep distribution of tryptase positive MCs in healthy controls, different stages of OSF and OSCC group ([Figure. 0](#pone-0000000-g000){ref-type="fig"}) {#s0c} --------------------------------------------------------------------------------------------------------------------------------------------------------  ![Deep distribution of tryptase positive mast cells.\ **A**, Healthy control. **B**, Stage 0 OSF. **C**, Stage 0 OSF. **D**, Stage 0 OSF. **E**, Stage 0 OSF. **F**, OSCC.](pone.0000000.g000){#pone-0000000-g000}  Deep