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Macrophage membrane proteins: possible role in the regulation of priming for enhanced respiratory burst activity
Abstract:
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.
Insights
Protease enzymes like trypsin prime macrophages to release more superoxide anion (O2-). This priming involves membrane protein modification, enhancing the respiratory burst response.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Macrophages play a crucial role in the immune response.
- The respiratory burst, involving superoxide anion (O2-) production, is a key microbicidal mechanism.
- Regulation of the respiratory burst is critical for effective immune function.
Purpose of the Study:
- To investigate the effect of protease exposure on macrophage priming.
- To elucidate the molecular mechanisms underlying protease-induced priming of the respiratory burst.
- To identify specific membrane proteins involved in regulating macrophage superoxide production.
Main Methods:
- Macrophages were briefly exposed to proteolytic enzymes (papain, elastase, trypsin).
- Superoxide anion (O2-) production was measured using spectrophotometric assays after stimulation with phorbol myristate acetate (PMA).
- Cell surface proteins were analyzed using radioiodination and gel electrophoresis.
Main Results:
- Protease treatment (papain, elastase, trypsin) primed macrophages for enhanced O2- production.
- Papain treatment cleaved a ~305 kDa membrane protein; C. parvum elicitation reduced ~305 kDa and ~270 kDa proteins; LPS elicitation reduced a ~175 kDa protein.
- Protease-treated cells exhibited a reduced lag time in O2- release.
- Inhibitors of protein synthesis augmented the priming effect.
Conclusions:
- Protease exposure primes macrophages for an enhanced respiratory burst.
- This priming is likely mediated by the inactivation of specific plasma membrane proteins that down-regulate O2- production.
- The findings suggest a novel regulatory mechanism for macrophage activation and the respiratory burst.