Thrombospondin-1 restrains neutrophil granule serine protease function and regulates the innate immune response during Klebsiella pneumoniae infection

Abstract

Neutrophil elastase (NE) and cathepsin G (CG) contribute to intracellular microbial killing but, if left unchecked and released extracellularly, promotes tissue damage. Conversely, mechanisms that constrain neutrophil serine protease activity protect against tissue damage but may have the untoward effect of disabling the microbial killing arsenal. The host elaborates thrombospondin-1 (TSP-1), a matricellular protein released during inflammation, but its role during neutrophil activation following microbial pathogen challenge remains uncertain. Mice deficient in thrombospondin-1 (thbs1−/−) showed enhanced lung bacterial clearance, reduced splenic dissemination, and increased survival compared with WT controls during intrapulmonary Klebsiella pneumoniae infection. More effective pathogen containment was associated with reduced burden of inflammation in thbs1−/− mouse lungs compared with WT controls. Lung NE activity was increased in thbs1−/− mice following Klebsiella pneumoniae challenge, and thbs1−/− neutrophils showed enhanced intracellular microbial killing that was abrogated with recombinant TSP-1 administration or WT serum. Thbs1−/− neutrophils exhibited enhanced NE and CG enzymatic activity and a peptide corresponding to amino acid residues 793–801 within the type 3 repeats domain of TSP-1 bridled neutrophil proteolytic function and microbial killing in vitro. Thus, TSP-1 restrains proteolytic action during neutrophilic inflammation elicited by Klebsiella pneumoniae, providing a mechanism that may regulate the microbial killing arsenal.

Moraxella catarrhalis Evades Host Innate Immunity via Targeting Cartilage Oligomeric Matrix Protein

“…Further, because host cells recognize and internalize M. catarrhalis through integrin a5b1-associated fibronectin in an opsonin-independent manner, the inhibition of phagocytosis could also be due to a blockade of M. catarrhalis-fibronectin-integrin association by the competitive binding of COMP to fibronectin and integrins (15,48). Interestingly, another thrombospondin family member, thrombospondin-1, which is localized in the epithelial layer of skin, blood, and myocardium, also inhibits phagocytosis of bacterial and fungal pathogens by neutrophils and macrophages in mouse models (49)(50)(51). Thrombospondin-1 restrains the activity of neutrophil elastase and enhances dissemination and infection of Klebsiella pneumoniae in mice (51).…”

“…Interestingly, another thrombospondin family member, thrombospondin-1, which is localized in the epithelial layer of skin, blood, and myocardium, also inhibits phagocytosis of bacterial and fungal pathogens by neutrophils and macrophages in mouse models (49)(50)(51). Thrombospondin-1 restrains the activity of neutrophil elastase and enhances dissemination and infection of Klebsiella pneumoniae in mice (51). Based on similar structures of thrombospondin-1 and COMP, COMP may use a similar pattern to block phagocytic killing and, therefore, promote M. catarrhalis infection of the respiratory tracts.…”

CD36 Provides Host Protection AgainstKlebsiella pneumoniaeIntrapulmonary Infection by Enhancing Lipopolysaccharide Responsiveness and Macrophage Phagocytosis

“…We sought to determine the contribution of this receptor to pulmonary host defense against the K2 strain, which is a well-known ATCC research strain that is pathogenic in mice [21]. At 24 and 48 hours following bacterial inoculation of 2 × 10 3 CFU, Cd36 −/− mice showed a higher bacterial burden in the lungs, compared with WT mice ( Figure 1A).…”

“…Initial studies indicated that the K. pneumoniae K2 strain grown to early logarithmic phase but not at the late logarithmic phase induced a reproducible pathogenic phenotype in the lungs of wild-type (WT) mice, and subsequent studies used an OD 600 nm of 0.2 to prepare the bacterial inoculum. We have previously described a detailed method of intratracheal administration of bacteria by direct visualization [21,23].…”

“…Using 3 distinct serotypes of the gram-negative pathogen K. pneumoniae-a research strain that expresses the K2 capsular polysaccharide serotype and is virulent in mice (hereafter, the "K2 strain") [21], a clinical strain that expresses the hypermucoviscous K1 capsular serotype causing liver and lung abscesses in Asia and is highly virulent in mice and humans (hereafter, the "K1 strain") [22], and a KPC-producing multidrug-resistant clinical strain (hereafter, the "K41 strain")-we show that CD36 is required for optimal control of K. pneumoniae in the lung and extrapulmonary bacterial dissemination to distant organ sites. In addition, we show that CD36 mediates recognition of LPS, enhances phagocytosis of K. pneumoniae by alveolar macrophages, and enhances JNK activation for optimal cytokine production in the lung.…”