REVERSIBLE EXPRESSION OF MOUSE MAST-CELL PROTEASE-2 MESSENGER-RNA ANDPROTEIN IN CULTURED MAST-CELLS EXPOSED TO IL-10

BALB/cJ mouse mast cells derived by culturing bone marrow progenitor c ells in WEHI-3 cell-conditioned medium (BMMC(W)) do not contain mouse mast cell protease 2 (mMCP-2) mRNA, but these cells can be induced to express this transcript after exposure to rIL-10. To study the transla tion and granule accumulation of mMCP-2 in rIL-10-treated BMMC (BMMC(W + IL-10)), a rabbit antibody was developed to a synthetic peptide tha t corresponds to the novel amino acid sequence in mMCP-2 at residues 5 6 to 71. After affinity purification, this antibody, anti-mMCP-2(56-71 ) IgG, reacted in SDS-PAGE/immunoblots against a 28-kDa protein in BMM C(W + IL-10) that had the N-terminal amino acid sequence of mMCP-2. As assessed immunohistochemically, mMCP-2 protein accumulated in the sec retory granules of Kirsten sarcoma virus-immortalized mouse mast cells , BMMC(W + IL-10), and the mucosal mast cells present in the jejunum o f Trichinella spiralis-infected BALB/cJ mice. Time course analyses of the induction of mMCP-2 mRNA and protein in BMMC(W + IL-10) revealed t hat these cells contain a high steady-state level of mMCP-2 mRNA 24 h after their exposure to rIL-10. Although a small amount of immunodetec table mMCP-2 protein is present in the cells treated for 24 h, large a mounts of this protease are not obtained until 7 days of treatment of the cells with rIL-10. Time course analyses of the loss of mMCP-2 mRNA and protein in BMMC(W + IL-10) revealed that the steady-state level o f mMCP-2 mRNA decreased dramatically 24 h after rIL-10 was removed fro m the culture medium, but that the level of mMCP-2 protein did not dec line measurably until day 5 of culture. The fact that the steady-state levels of mMCP-2 mRNA and protein in BMMC can both be reversibly alte red by culturing these mast cells in the presence and absence of rIL-1 0 suggests that the phenotype of mast cells is not fixed. Rather, it i s in a dynamic state regulated by the cytokine network to which mast c ells are exposed in their different microenvironments.