Neutrophil degranulation mediates severe lung damage triggered by streptococcal M1 protein

Abstract

Streptococcus pyogenes of the M1 serotype can cause streptococcal toxic shock syndrome commonly associated with acute lung injury. The aim of the present study was to investigate the role of neutrophils and their secretion products in M1 protein-induced lung damage.The degranulation of neutrophils by M1 protein was studied in whole blood using marker analysis for individual granule subsets. In mice, M1 protein was injected intravenously and the lung damage was assessed by histology, electron microscopy, cell count in bronchoalveolar lavage fluid and analysis of lung vascular permeability. Comparisons were made in mice with intact white blood count, neutropenic mice and neutropenic mice injected with the secretion of activated neutrophils.In whole blood, M1 protein forms complexes with fibrinogen that bind to b 2 -integrins on the neutrophil surface, resulting in degranulation of all four subsets of neutrophil granules. Intravenous injection of M1 protein into mice induced neutrophil accumulation in the lung, increase in vascular permeability and acute lung damage. Depletion of neutrophils from the circulation completely abrogated lung injury and vascular leakage. Interestingly, the lung damage was restored by injecting neutrophil secretion.The present data suggest that neutrophil granule proteins are directly responsible for lung damage induced by the streptococcal M1 protein.

Neutrophil-Derived Hyperresistinemia in Severe Acute Streptococcal Infections

“…In contrast, the heparinbinding protein, highly expressed in severe streptococcal infections and linked to acute vascular leakage, is stored within the secretory vesicles, which are the most readily mobilized granules (20). Taken together, these findings are in line with recent studies underscoring the central role of streptococcus-triggered neutrophil activation and degranulation in the induction of shock and acute organ injury (21,26). In vitro studies of neutrophil and resistin responses confirmed that neutrophils represent a major source of the resistin mobilized in response to bacterial infection.…”

“…One likely candidate was the streptococcal M1 protein that has recently received a lot of attention due to its immunostimulatory activity (18,26,27). Most pertinent to this study is its role as a mediator of potent activation and degranulation of neutrophils that result in vascular leakage and septic shock as well as acute lung injury (21,26). This occurs when soluble M1 protein forms complexes with fibrinogen, which are potent activators of neutrophils through interaction with ␤ 2 -integrins.…”

“…After nuclei and unbroken cells were sedimented by centrifugation, the postnuclear supernatant was separated on Percoll gradients and the localization of subcellular organelles in the gradients was determined by marker analysis of the fractions. Relative amounts of MPO (marker for the azurophil granules), lactoferrin (specific granules), and CD35 (secretory vesicles) were tested by Western blotting for MPO and lactoferrin and by dot blot analysis for CD35 using Abs against respective marker, as described elsewhere (21).…”

Neutrophil-derived azurocidin alarms the immune system

“…In the course of the infection, S. pyogenes shed M1 protein, which forms complexes with fibrinogen [68]. These activate PMN to degranulate in the circulation [69], releasing proteins from all granule subsets, including azurocidin [68]. Degranulation of PMN was found to be causative of the subsequent lung damage and edema formation [69].…”

“…Streptococcus pyogenes infections may lead to the streptococcal toxic shock syndrome, which is characterized by hypotension, multiple organ failure, and lung edema. In the course of the infection, S. pyogenes shed M1 protein, which forms complexes with fibrinogen [68]. These activate PMN to degranulate in the circulation [69], releasing proteins from all granule subsets, including azurocidin [68].…”