CMA1 and infection: To address if the mast cell-specific protease chymase mMCP-4 would have an impact on the protection of the host during infection with G. intestinalis, we infected seven to 13 weeks old (referred to as young) and 18 to 36 weeks old (referred to as mature adult) congenic mMCP-4+/+, mMCP-4+/− and chymase-deficient mMCP-4−/− littermate mice in a series of completely blinded experiments (Table 1).