Mast cells in the rat liver are phenotypically heterogeneous and exhibit features of immaturity

Gastrointestinal hypersensitivity to food allergens is a significant but relatively poorly understood allergic disease. Recent evidence from a rat model of IgE‐mediated gastrointestinal hypersensitivity has suggested that hepatic mast cells (HMC) may play an important role in such reactions. The present study was undertaken to better define their phenotype. Livers from Australian albino Wistar (AaW), Brown Norway (BN) and PVG/c rats were examined using traditional histological techniques and reverse transcription–polymerase chain reaction (RT‐PCR). Hepatic mast cells were overwhelmingly Alcian blue positive, sensitive to formalin fixation and predominantly rat mast cell protease (RMCP) 1+/2– (AaW 57%; BN 53%). Such a phenotype has previously been associated with an immature mast cell phenotype. A significant number of HMC also stained RMCP 1–/2+ (AaW 15%; BN 19%) or were RMCP 1+/2+ (AaW 24%; BN 26%). In contrast to previous reports, RT‐PCR showed that the liver expressed mRNA of other mast cell proteases, including the chymase RMCP 5 as well as two tryptases, RMCP 6 and RMCP 7. These results suggest that HMC are a heterogeneous population of mast cells with some characteristics previously associated with immature cells.