Macrophage membrane proteins: possible role in the regulation of priming for enhanced respiratory burst activity.

Brief exposure of macrophages to the proteolytic enzymes papain, elastase, or trypsin primed them for enhanced production of superoxide anion (O2-) in response to stimulation by phorbol myristate acetate (PMA). Priming by trypsin was achieved at 0 degree C, at which temperature trypsin functions as a protease but is not internalized, supporting the concept that protease priming depends on modification of the plasma membrane. Analysis of external membrane proteins after radioiodination of intact cells and separation by gel electrophoresis indicated that papain treatment of macrophages resulted in the cleavage of a membrane protein with a molecular weight of approximately 305K. Membranes from macrophages primed by elicitation with Corynebacterium parvum also demonstrated a reduced amount of the membrane protein at approximately 305 kDa, as well as a reduction of a protein at about 270 kDa. Lipopolysaccharide-elicited macrophages showed a reduced amount of a protein at about 175 kDa. Continuous spectrophotometric assays of O2- release from adherent macrophages indicated that after exposure to a stimulus, protease-treated cells produced O2- more quickly than did control cells (reduced lag time). Inhibitors of protein synthesis augmented the priming effect of papain when added with the protease. These results suggest that protease-induced priming results from inactivation of a membrane protein (or proteins) that exerts a down-regulating effect on the respiratory burst.