Mast cell chymase: a useful serum marker in anaphylaxis

RATIONALE: The reliable diagnosis of anaphylaxis can present challenge. We have explored mast cell chymase as a potential marker for anaphylaxis.METHODS: A sandwich-based ELISA was developed with monoclonal antibodies we have prepared against chymase, and validated for application to serum samples. The enzymatic activity of chymase was determined in parallel using the chromogenic substrates suc-AAPF-pNA and RETF-4NA. Tryptase, carboxypeptidase and DPPI were measured by ELISA. Serum was collected from cases of anaphylaxis provoked by food, drug and insect stings (n=181); from healthy blood donors (n=123); and from patients allergic to food (n=76) or drugs (n=26).RESULTS: The ELISA allowed detection of chymase in all serum samples, and values obtained were unaffected by the presence of alpha-2-macroglobulin or other inhibitors. Chymase levels in serum collected from patients within 8h of anaphylaxis were greater than those in the control group (p=0.0069); and concentrations remained high at least 24h after onset of the reaction. Chymase levels in anaphylaxis correlated with levels of mast cell carboxypeptidase and with dipeptidyl peptidase 1 (DPPI), but not tryptase. Concentrations of chymase measured by ELISA were weakly associated with serum chymase activity. Addition of DPPI to serum increased the chymase activity in samples collected prior to allergen challenge (p=0.0008) consistent with the presence of pro-forms of chymase in the circulation. However, DPPI-induced increases in serum chymase activity were not observed in samples collected following a reaction (when serum DPPI concentrations were elevated).CONCLUSIONS: Measurement of mast cell chymase in serum should be useful as a means for laboratory confirmation of anaphylaxis