, 2010). Truly nonencapsulated pneumococci may be a cause of outbreaks of mucosal disease particularly conjunctivitis and have been related to acute otitis media (Martin et al., 2003; Hanage et al., 2006). Thus, nonencapsulated pneumococci MLN0128 in vitro may be highly contagious and cause mucosal disease (Martin et al., 2003). The microbial and host factors that determine carriage are still incompletely characterized. Neutrophils recruited by IL-17 expressing CD4+
T cells seem to contribute to mucosal clearance of pneumococci (Malley et al., 2005; Zhang et al., 2009). Neutrophils kill and degrade bacteria by a range of mechanisms including reactive oxygen species and antimicrobial peptides. The concept has emerged that neutrophil proteases such as neutrophil elastase and cathepsin G also contribute significantly to intracellular and extracellular killing of bacteria Dabrafenib clinical trial (Reeves et al., 2002; Pham, 2006). Thus, neutrophil proteases may be effective in killing bacteria even in the absence of effective phagocytosis. Patients with
deficiency of neutrophil serine protease activity due to Papillon–Lefevre syndrome suffer impaired host defence clinically evident as severe periodontitis and pyogenic liver and renal abscesses (Van Dyke et al., 1984; Almuneef et al., 2003). The importance of neutrophil elastase and cathepsin G for intracellular and extracellular killing of S. pneumoniae by neutrophils was demonstrated recently and may be relevant for colonization (Standish & Weiser, 2009). Extracellular neutrophil protease is present
on the conjunctival and nasal mucosa as it can be demonstrated in tear fluid and nasal secretions (Sakata et al., 1997; Innes et al., 2009). The prevalence of nonencapsulated pneumococci on mucosal surfaces compared to the almost complete absence of nonencapsulated pneumococci in invasive disease suggests nonencapsulated pneumococci possess resistance to important mucosal defences. Indeed, nonencapsulated pneumococci possess greater resistance to cationic antimicrobial peptides (the ∝-defensin human neutrophil protein 1–3) (Peschel, 2002; Beiter et al., 2008). The aim of this study was to investigate the effect of the presence of capsule on the in vitro pneumococcal resistance to extracellular human neutrophil elastase and else cathepsin G. The in vitro bactericidal activities of elastase and cathepsin G were determined as described previously (Standish & Weiser, 2009). In brief, original cultures of pneumococcal wild-type strains and nonencapsulated derivatives (wild-type strain D39 (serotype 2), TIGR4 (serotype 4) and G54 (serotype 19F) and isogenic nonencapsulated derivatives) (Bootsma et al., 2007), were grown to mid-log in tryptic soy broth (TSB) at 37 °C, 5% CO2 without agitation, washed twice in PBS, and then ~ 107 CFU/mL S. pneumoniae were incubated in the presence or absence (control) of purified human 3.39 μM neutrophil elastase (NE; Calbiochem Cat. No. 324681) and 2.