Background: Mast cells play crucial roles in the pathogenesis of allergies through the secretion of powerful mediators, prominent among which is a group of proteases that are stored and function within the intracellular granules of mast cells.
Objectives: We aimed to investigate the secretion of these proteases from mast cells during degranulation and to explore the factors that can influence the secretion and gene expression of mast cell mediators.
Materials and methods: Mast cell line (LAD2) were stimulated to degranulate with calcium ionophore A23187 (CaI) or substance P (SP).  Gene expressions of dipeptidyl peptidase I (DPPI) and carboxypeptidase A3 (CPA3), chymase (CHY), tryptase (TRY) were determined by quantitative RT-PCR.  Alterations in gene expression were investigated at time points ranging from 0.5 to 6 hours following cell stimulation. Beta-hexosaminidase activity and DPPI levels were measured using ELISA. 
Results: Experimental stimulation of sensitized mast cells by CaI or SP, revealed by the release of the activation marker β-hexosaminidase in a time dependent manner (net release=63% ± 2.4 at 6 h),  this was associated with significant increases in gene expression for DPPI and also for CPA3, CHY and TRY. Cal sensitization produced a significant increase in DPPI, CPA3 and CHY in the first 30m of stimulation with gradual decrease in levels with time but still significantly higher than non-stimulated cells (p≤0.05 for all). The reverse for TRY, as the most significant increase in its expression was at 2H. SP produced a gradual increase in gene expression for all studied parameters (p≤0.05 for all) with the most significant increase was for TRY gene at 2h (p˂0.01 vs cal).
Conclusion: DPPI can be released from mast cells on degranulation, and the subsequent increases in gene expression would be consistent with the later replenishment of secretory granules.  This protease may participate in processes of protease activation and other activities outside the cell in inflammatory disease. Thus, DPPI could be represented as an innovative marker for mast cell sensitization which may accurately diagnose the allergic responses specially when measured as panel with CPA3, CHY and TRY.