Mapping of the rat mast cell granule proteinases RMCPI and II by enzyme-linked immunosorbent assay and paired immunofluorescence.

The distribution of the rat mast cell granule proteinases, rat mast cell proteinase I and II (RMCPI and II respectively) has been determined in rat tissues with the aid of highly sensitive and specific enzyme-linked immunosorbent assays (ELISA) and paired immunofluorescence. The major source of RMCPII is the gastrointestinal tract, although low concentrations were also detected in non-mucosal sites including thymus, mesenteric lymph nodes, liver, bone marrow, heart, kidney and spleen. Cellular localization by paired immunofluorescence showed that most cells contained either RMCPI or RMCPII, although a minor subpopulation in which individual cells contained both proteinases was also identified in a few tissues. RMCPII-containing cells predominated at mucosal surfaces but were also found in non-mucosal tissues. Individual cells expressing both RMCPI and II were present in lung, liver mesenteric lymph node and submucosa of stomach and were occasionally represented amongst serosal cells from the peritoneal cavity. Connective tissue mast cells of skin and tongue were identified as major sources of RMCPI, although this proteinase was widely distributed in all tissues examined. The present study demonstrates the heterogeneity of mast cell proteinase phenotypes in the rat and emphasises the difficulties in determining mast cell subtypes on tissue location alone.