Staphylococcal Superantigen-Like Protein 1 and 5 (SSL1 & SSL5) Limit Neutrophil Chemotaxis and Migration through MMP-Inhibition.

Matrix metalloproteinases (MMPs) are endopeptidases that degrade components of the extracellular matrix, but also modulate inflammation. During bacterial infections, MMPs are important in the recruitment and migration of inflammatory cells. Besides facilitating cell migration by degrading extracellular matrix components, they potentiate the action of several inflammatory molecules, including cytokines, chemokines, and antimicrobial peptides. Staphylococcus aureus secretes an arsenal of immune evasion molecules that interfere with immune cell functioning and hamper proper immune responses. An earlier study identified staphylococcal superantigen-like protein 5 (SSL5) as an MMP9 inhibitor. Since multiple MMPs are involved in neutrophil recruitment, we set up an in-depth search for additional MMP inhibitors by testing a panel of over 70 secreted staphylococcal proteins on the inhibition of the two main neutrophil MMPs: MMP8 (neutrophil collagenase) and MMP9 (neutrophil gelatinase B). We identified SSL1 and SSL5 as potent inhibitors of both neutrophil MMPs and show that they are actually broad range MMP inhibitors. SSL1 and SSL5 prevent MMP-induced cleavage and potentiation of IL-8 and inhibit the migration of neutrophils through collagen. Thus, through MMP-inhibition, SSL1 and SSL5 interfere with neutrophil activation, chemotaxis, and migration, all vital neutrophil functions in bacterial clearance. Studies on MMP-SSL interactions can have therapeutic potential and SSL based derivatives might prove useful in treatment of cancer and destructive inflammatory diseases.

Pneumococcal immune evasion: ZmpC inhibits neutrophil influx.

Neutrophil recruitment is essential in clearing pneumococcal infections. The first step in neutrophil extravasation involves the interaction between P-selectin on activated endothelium and P-Selectin Glycoprotein 1 (PSGL-1) on neutrophils. Here, we identify pneumococcal Zinc metalloproteinase C as a potent inhibitor of PSGL-1. ZmpC degrades the N-terminal domain of PSGL-1, thereby disrupting the initial rolling of neutrophils on activated human umbilical vein endothelial cells. Furthermore, mice infected with wild-type strain in the model of pneumococcal pneumonia showed lower lungs neutrophil infiltration compare to animals infected with ZmpC mutant. In addition, we confirmed the association of zmpC with serotype 8 and 11A and found it to be associated with serotype 33F as well. In conclusion, wereport PSGL-1 as a novel target for ZmpC and show that ZmpC inhibits neutrophil extravasation during pneumococcal pneumonia.

Identification of an immunomodulating metalloprotease of Pseudomonas aeruginosa (IMPa).

Phagocytosis by neutrophils is the essential step in fighting Pseudomonas infections. The first step in neutrophil recruitment to the site infection is the interaction of P-selectin (on endothelial cells) with P-selectin glycoprotein ligand-1 (PSGL-1) on neutrophils. Pseudomonas aeruginosa secretes various proteases that degrade proteins that are essential for host defence, such as elastase and alkaline protease. Here we identify PA0572 of P. aeruginosa as an inhibitor of PSGL-1 and named this secreted hypothetical protease immunomodulating metalloprotease of P. aeruginosa or IMPa. Proteolytic activity was confirmed by cleavage of recombinant and cell-surface expressed PSGL-1. Functional inhibition was demonstrated by impaired PSGL-1-mediated rolling of IMPa-treated neutrophils under flow conditions. Next to PSGL-1, IMPa targets CD43 and CD44 that are also involved in leucocyte homing. These data indicate that IMPa prevents neutrophil extravasation and thereby protects P. aeruginosa from neutrophil attack.