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Open AccessArticle

Human Neutrophil Granule Exocytosis in Response to Mycobacterium smegmatis

Department of Microbiology & Immunology, School of Medicine, University of Louisville, 505 S. Hancock St., Louisville, KY 40202, USA
Department of Medicine, School of Medicine, University of Louisville, 570 S. Preston St., Louisville, KY 40202, USA
Authors to whom correspondence should be addressed.
Pathogens 2020, 9(2), 123;
Received: 12 July 2019 / Revised: 5 February 2020 / Accepted: 12 February 2020 / Published: 15 February 2020
(This article belongs to the Section Human Pathogens)
Mycobacterium smegmatis rarely causes disease in the immunocompetent, but reported cases of soft tissue infection describe abscess formation requiring surgical debridement for resolution. Neutrophils are the first innate immune cells to accumulate at sites of bacterial infection, where reactive oxygen species and proteolytic enzymes are used to kill microbial invaders. As these phagocytic cells play central roles in protection from most bacteria, we assessed human neutrophil phagocytosis and granule exocytosis in response to serum opsonized or non-opsonized M. smegmatis mc2. Although phagocytosis was enhanced by serum opsonization, M. smegmatis did not induce exocytosis of secretory vesicles or azurophilic granules at any time point tested, with or without serum opsonization. At early time points, opsonized M. smegmatis induced significant gelatinase granule exocytosis compared to non-opsonized bacteria. Differences in granule release between opsonized and non-opsonized M. smegmatis decreased in magnitude over the time course examined, with bacteria also evoking specific granule exocytosis by six hours after addition to cultured primary single-donor human neutrophils. Supernatants from neutrophils challenged with opsonized M. smegmatis were able to digest gelatin, suggesting that complement and gelatinase granule exocytosis can contribute to neutrophil-mediated tissue damage seen in these rare soft tissue infections. View Full-Text
Keywords: human neutrophils; granule exocytosis; environmental mycobacteria human neutrophils; granule exocytosis; environmental mycobacteria
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Miralda, I.; Klaes, C.K.; Graham, J.E.; Uriarte, S.M. Human Neutrophil Granule Exocytosis in Response to Mycobacterium smegmatis. Pathogens 2020, 9, 123.

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