Increased Susceptibility of Humanized NSG Mice to Panton-Valentine Leukocidin and Staphylococcus aureus Skin Infection

Abstract

Staphylococcus aureus is a leading cause of skin and soft-tissue infections worldwide. Mice are the most commonly used animals for modeling human staphylococcal infections. However a supra-physiologic S. aureus inoculum is required to establish gross murine skin pathology. Moreover, many staphylococcal factors, including Panton-Valentine leukocidin (PVL) elaborated by community-associated methicillin-resistant S. aureus (CA-MRSA), exhibit selective human tropism and cannot be adequately studied in mice. To overcome these deficiencies, we investigated S. aureus infection in non-obese diabetic (NOD)/severe combined immune deficiency (SCID)/IL2rγnull (NSG) mice engrafted with human CD34+ umbilical cord blood cells. These “humanized” NSG mice require one to two log lower inoculum to induce consistent skin lesions compared with control mice, and exhibit larger cutaneous lesions upon infection with PVL+ versus isogenic PVL- S. aureus. Neutrophils appear important for PVL pathology as adoptive transfer of human neutrophils alone to NSG mice was sufficient to induce dermonecrosis following challenge with PVL+ S. aureus but not PVL- S. aureus. PMX53, a human C5aR inhibitor, blocked PVL-induced cellular cytotoxicity in vitro and reduced the size difference of lesions induced by the PVL+ and PVL- S. aureus, but PMX53 also reduced recruitment of neutrophils and exacerbated the infection. Overall, our findings establish humanized mice as an important translational tool for the study of S. aureus infection and provide strong evidence that PVL is a human virulence factor.

Humanized Mice Exhibit Increased Susceptibility toStaphylococcus aureusPneumonia

“…One study examined the role of PVL in skin infection. This study used a neonatal model of humanized mice, whereby pups are transferred with CD34 + cells without irradiation and thymic transplantation [47]. They too achieved high engraftment rates and saw a predominance of T lymphocytes over myeloid cells in the spleen.…”

“…They too achieved high engraftment rates and saw a predominance of T lymphocytes over myeloid cells in the spleen. Subcutaneously infected humanized mice were more susceptible to infection, requiring a lower dose to achieve lesion sizes analogous to those in a standard C57BL/6J mouse [47]. Inactivation of PVL led to reduced lesion sizes but no changes in bacterial burden, and the nature of the immune cells involved in clearance was not defined.…”

Virulence Factor Targeting of the Bacterial Pathogen Staphylococcus aureus for Vaccine and Therapeutics

“…Work by Tseng and others were able to generate humanized mice using CD24+ cells from umbilical blood that require one-two log less inoculum of S. aureus to generate lesions [156]. This decreased inoculum brings the CFU count of S. aureus down to the estimated human range of infection of 10 5 or 10 6 CFU [156–158].…”

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.…”