Simultaneous induction of HSP70 expression, and degranulation, in IgE/Ag‐stimulated or extracellular HSP70‐stimulated mast cells

Abstract Background In mast cells, induction of HSP 70 expression during antigen stimulation has not been reported. Methods Mouse bone marrow‐derived mast cells ( BMMC ) were stimulated with IgE/Ag or HSP 70. Induction of HSP 70 expression and signaling protein phosphorylation were evaluated by immunoblotting. Results HSP 70 expression is induced in BMMC at an early stage of IgE/Ag‐dependent stimulation, some of which is released from the cells in a granule‐associated form. Induction of HSP 70 expression was also observed with an IgE/Ag‐stimulated human basophilic cell line, indicating that the phenomenon is not restricted to mouse BMMC . The induction of HSP 70 expression, and its release, followed a similar time course to that of degranulation. Released HSP 70 seems to be responsible for degranulation and production of eicosanoids, at least in part, because a neutralizing anti‐ HSP 70 antibody mitigated these activities and because exogenous HSP 70 not only induced immediate degranulation followed by autocrine HSP 70 expression but also enhanced degranulation in IgE/Ag‐stimulated BMMC . Extracellular HSP 70 was found to induce phosphorylation of linker for activation of T cells ( LAT ) and a series of downstream signaling molecules in BMMC . We further found that Fyn, Lyn, and spleen tyrosine kinase (Syk), which are known to concern LAT phosphorylation in IgE/Ag‐stimulated BMMC , were not phosphorylated in HSP 70‐stimulated BMMC , whereas lymphocyte‐specific protein tyrosine kinase (Lck) was phosphorylated. Conclusion Fcε RI stimulation in BMMC and basophils induces HSP 70 expression and its release. Extracellular HSP 70 induces degranulation and mediator release via phosphorylation of LAT .