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Functional inactivation and structural disruption of human alpha 2-macroglobulin by neutrophils and eosinophils
V Y Reddy1, S V Pizzo, S J Weiss
1Department of Internal Medicine, Simpson Memorial Research Institute, University of Michigan, Ann Arbor 48109.
Abstract:
Human alpha 2-macroglobulin (alpha 2M) rapidly lost functional and structural integrity in the course of a short-term incubation with either triggered neutrophils or eosinophils. In contrast to native alpha 2M, the modified antiproteinase was unable to bind neutrophil elastase or pancreatic elastase in a manner that restricted the enzymes' access to high molecular weight substrates. In addition to the complete loss of its antiproteolytic potential, the conformation of the dysfunctional inhibitor was radically altered and susceptible to further modification by exogenous proteinases as assessed by polyacrylamide gel electrophoresis. Analysis of the mechanism by which alpha 2M was inactivated by neutrophils revealed that the process was dependent on the generation of hypochlorous acid, an oxidant generated by the hydrogen peroxide-myeloperoxidase-chloride system. In contrast to the neutrophil, maximal eosinophil-dependent inactivation required the presence of physiologic concentrations of bromide and appeared to involve the generation of hypobromous acid. The ability of either hypochlorous acid or hypobromous acid to directly disrupt alpha 2M function and structure was confirmed under cell-free conditions. These results demonstrate that alpha 2M, an antiproteinase heretofore considered to be resistant to physiologic inactivation, could be destroyed by two populations of human phagocytes via oxidative modifications mediated by hypophalous acids.
Insights
Human alpha 2-macroglobulin (alpha 2M), an antiproteinase, is rapidly inactivated by neutrophils and eosinophils. Oxidative modifications by hypohalous acids disrupt alpha 2M function and structure, challenging its resistance to physiologic inactivation.
Area of Science:
- Biochemistry
- Immunology
- Cell Biology
Background:
- Human alpha 2-macroglobulin (alpha 2M) is a key antiproteinase in plasma.
- Alpha 2M is generally considered resistant to physiological inactivation.
- Neutrophils and eosinophils are crucial phagocytes in the innate immune system.
Purpose of the Study:
- To investigate the susceptibility of alpha 2M to inactivation by human neutrophils and eosinophils.
- To elucidate the mechanisms underlying alpha 2M inactivation by these phagocytes.
- To determine the role of oxidants in the degradation of alpha 2M.
Main Methods:
- Incubation of alpha 2M with triggered neutrophils and eosinophils.
- Assessing alpha 2M's ability to inhibit elastase activity.
- Analyzing structural changes in alpha 2M using polyacrylamide gel electrophoresis.
- Investigating the role of hypochlorous acid and hypobromous acid in alpha 2M inactivation under cell-free conditions.
Main Results:
- Alpha 2M rapidly lost functional and structural integrity upon incubation with neutrophils or eosinophils.
- Inactivated alpha 2M could not inhibit neutrophil or pancreatic elastase.
- Neutrophil-mediated inactivation involved hypochlorous acid (HOCl).
- Eosinophil-mediated inactivation required bromide and involved hypobromous acid (HOBr).
- Both HOCl and HOBr directly disrupted alpha 2M structure and function.
Conclusions:
- Alpha 2M is susceptible to oxidative inactivation by human neutrophils and eosinophils.
- Hypohalous acids, HOCl and HOBr, are key mediators of alpha 2M destruction.
- These findings challenge the long-held view of alpha 2M's resistance to physiological inactivation.