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 r esponse to stress. Here we describe the effect of heat shock induced b y elevated temperatures on the processing and presentation of an exoge nous Ag, cytochrome c, to an Ag-specific class Ii-restricted T cell hy brid. Heat shock markedly enhances processing of Ag entering the B cel l 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 shoc k 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 measur able 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 cl ass II purified from cells grown at 37 degrees C, indicating that clas s II formed during a stress response is not identical to that formed u nder normal conditions. The effect of heat shock on B cell Ag processi ng reported here is likely to be relevant to processing in vivo, which may often proceed under conditions that induce the heat shock respons e, such as during viral or bacterial infections, inflammation, and fev er.