Heat shock enhances antigen processing and accelerates the formation of compact class II alpha beta dimers

The heat shock response is a universal and highly conserved cellular response to stress. Here we describe the effect of heat shock induced by elevated temperatures on the processing and presentation of an exogenous Ag, cytochrome c, to an Ag-specific class II-restricted T cell hybrid. Heat shock markedly enhances processing of Ag entering the B cell either through fluid phase pinocytosis or through receptor-mediated endocytosis. B cells undergoing a stress response require less time to process and present Ag and achieve higher levels of T cell activation as compared with control cells. Augmented processing and presentation requires that the Ag be present during the stress response. Heat shock has no effect on the presenting ability of B cells that had already processed Ag; and heat shock in the absence of Ag has little effect on subsequent processing or presentation of Ag. Heat shock has no measurable effect on the cell surface expression of class II as measured by flow cytometry but markedly accelerates the formation of compact alpha beta dimers in B cells. The class II purified from heat shocked cells is more active in Ag presentation assays in vitro as compared with class II purified from cells grown at 37 degrees C, indicating that class II formed during a stress response is not identical to that formed under normal conditions. The effect of heat shock on B cell Ag processing reported here is likely to be relevant to processing in vivo, which may often proceed under conditions that induce the heat shock response, such as during viral or bacterial infections, inflammation, and fever.