Humanized Mice Exhibit Increased Susceptibility toStaphylococcus aureusPneumonia

Abstract

Staphylococcus aureus is a highly successful human pathogen that has evolved in response to human immune pressure. The common USA300 methicillin-resistant S. aureus (MRSA) strains express a number of toxins, such as Panton-Valentine leukocidin and LukAB, that have specificity for human receptors. Using nonobese diabetic (NOD)-scid IL2Rγ null (NSG) mice reconstituted with a human hematopoietic system, we were able to discriminate the roles of these toxins in the pathogenesis of pneumonia. We demonstrate that expression of human immune cells confers increased severity of USA300 infection. The expression of PVL but not LukAB resulted in more-severe pulmonary infection by the wild-type strain (with a 30-fold increase in the number of colony-forming units/mL; P < .01) as compared to infection with the lukS/F-PV (Δpvl) mutant. Treatment of mice with anti-PVL antibody also enhanced bacterial clearance. We found significantly greater numbers (by 95%; P < .05) of macrophages in the airways of mice infected with the Δpvl mutant compared with those infected with the wild-type strain, as well as significantly greater expression of human tumor necrosis factor and interleukin 6 (84% and 51% respectively; P < .01). These results suggest that the development of humanized mice may provide a framework to assess the contribution of human-specific toxins and better explore the roles of specific components of the human immune system in protection from S. aureus infection.Keywords. Staphylococcus aureus; pneumonia; lung; respiratory; host-pathogen; humanized; mouse model; PVL; Panton-Valentine leukocidin.Staphylococcus aureus is a well-recognized human pathogen associated with infection in diverse hosts; it is an important cause of healthcare-associated infection but also a major cause of morbidity and mortality in healthy patients with no factors predisposing them to infection. Nasal colonization with S. aureus is associated with subsequent infection and occurs in up to 30% of unselected individuals [1,2]. Yet, despite the prevalence of S. aureus in the general population, the specific correlates of protective immunity against staphylococcal infection are not well defined.A number of S. aureus virulence factors, including several bicomponent toxins, are specific for human receptors [3,4]. One of the first of these human-specific toxins to be fully characterized was Panton-Valentine leukocidin (PVL), which targets neutrophils, macrophages, and monocytes [5,6]. Although epidemiologically linked to severe infection in humans [7,8], the PVL null mutant (lukS/lukF) did not consistently demonstrate the expected phenotype in murine models [5,[8][9][10][11][12][13], although it was significantly attenuated in rabbit models of pneumonia [5]. The molecular basis for this discrepancy was ascribed to the high human (and rabbit) specificity for the PVL receptors, C5aR and C5L2 [14]. Additional toxins, LukAB and HlgCB, have also been shown to have high specificity to the human forms of the receptors, CD11b and C5aR, respectively [4,14,15]. These ...

Animal models of hospital-acquired pneumonia: current practices and future perspectives

“…A recent study using NSG (NOD scid gamma) background mouse strain grafted with human CD34 cells showed increased susceptibility towards clinical isolate USA300 S. aureus strain compared to wild type animals (113). Furthermore, this study identified specific bacterial toxins that were more effective in the humanized mouse strain (113). This indicates that specific host-pathogen interactions drive pneumonia development and illustrates the importance of humanized animal models to study HAP.…”

“…A humanized bacterial pneumonia model could offer significant advantages over wild type animals. A recent study using NSG (NOD scid gamma) background mouse strain grafted with human CD34 cells showed increased susceptibility towards clinical isolate USA300 S. aureus strain compared to wild type animals (113). Furthermore, this study identified specific bacterial toxins that were more effective in the humanized mouse strain (113).…”

Staphylococcus aureus pore-forming toxins: The interface of pathogen and host complexity

“…Recent approaches to addressing PVL pathobiology have attempted to circumvent the lack of PVL interaction with murine receptors by using humanized mice models, in which immune incompetent NSG (non-obese diabetic/severe combined immune deficiency/IL2rγ null or NOD.Cg- Prkdc scid Il2rg 1Wjl /SzJ) mice are engrafted with human hematopoietic cells from cord blood (CD34 + ) [145]. These mice are highly susceptible to dermonecrosis and pneumonia caused by PVL-expressing S. aureus in a human PMN-dependent manner [146, 147]. These model systems may provide further insights regarding PVL activity involving the immune response.…”

Targeting fundamental pathways to disrupt Staphylococcus aureus survival: clinical implications of recent discoveries

“…More recently, several reports have addressed modeling S. aureus infections in so-called "humanized" mice (160)(161)(162), which are immunocompromised animals engineered to accept human hematopoietic stem cells and subsequently develop a human immune system (163). Initial reports indicate that humanized mice in the NOD/SCID γ (NSG) background may be an improved model, as a reduced inoculum (up to 1-2 logs lower than that required for WT mice in the soft-tissue model) is able to induce dermonecrosis.…”

“…Initial reports indicate that humanized mice in the NOD/SCID γ (NSG) background may be an improved model, as a reduced inoculum (up to 1-2 logs lower than that required for WT mice in the soft-tissue model) is able to induce dermonecrosis. Moreover, humanized NSG mice exhibit a pathologic phenotype for factors with selective human tropism (160)(161)(162). However, the high cost; the potential confounding by nonimmune compartments, such as epithelial cells; and the incomplete humanization of the immune system, including low neutrophil counts and lack of complement, remain barriers for general acceptance of the model.…”