Staphylococcus aureus Alpha Toxin Suppresses Effective Innate and Adaptive Immune Responses in a Murine Dermonecrosis Model

Abstract

An optimal host response against Staphylococcus aureus skin and soft tissue infections (SSTI) is dependent on IL-1β and IL-17 mediated abscess formation. Alpha toxin (AT), an essential virulence factor for SSTI, has been reported to damage tissue integrity; however its effect on the immune response has not been investigated. Here, we demonstrate that infection with USA300 AT isogenic mutant (Δhla), or passive immunization with an AT neutralizing mAb, 2A3, 24 h prior to infection with wild type USA300 (WT), resulted in dermonecrotic lesion size reduction, and robust neutrophil infiltration. Infiltration correlates with increase in proinflammatory cytokines and chemokines, as well as enhanced bacterial clearance relative to immunization with a negative control mAb. In addition, infection with Δhla, or with WT +2A3, resulted in an early influx of innate IL-17+γδT cells and a more rapid induction of an adaptive immune response as measured by Th1 and Th17 cell recruitment at the site of infection. These results are the first direct evidence of a role for AT in subverting the innate and adaptive immune responses during a S. aureus SSTI. Further, these effects of AT can be overcome with a high affinity anti-AT mAb resulting in a reduction in disease severity.

The psm α Locus Regulates Production of Staphylococcus aureus Alpha-Toxin during Infection

“…3A) and dermonecrotic skin lesion area (Fig. 3B) compared to WT S. aureus, consistent with previously reported observations (15,21,28,42). S. aureus recovery (CFU) from skin abscesses was similar among all three strains at the 30-h time point (Fig.…”

“…The observed reduction in Hla expression by psm mutant strains in vitro suggested that the attenuated dermonecrosis phenotype observed upon skin infection with the S. aureus ⌬psm␣ psm␤ hld strain was potentially attributable to the loss of Hla activity. In murine and rabbit model systems, disruption of Hla expression or receptor availability results in a moderate reduction in overall skin abscess size but a near-complete attenuation of epidermal injury, corresponding to the maintenance of E-cadherin-based intercellular adherens junctions (15,21,24,42). To determine whether psm loci have a regulatory effect on Hla production in vivo, we performed a comparative analysis of Hla Ϫ and PSM Ϫ strains in the skin and soft tissue model of infection.…”

Anti-Alpha-Toxin Monoclonal Antibody and Antibiotic Combination Therapy Improves Disease Outcome and Accelerates Healing in a Staphylococcus aureus Dermonecrosis Model

“…We previously reported on the prophylactic efficacy and mechanism of action of an anti-AT MAb, 2A3, in the murine dermonecrosis model (9,18). To assess the potential of an AT-neutralizing MAb as a therapeutic for S. aureus skin and soft tissue infections, the therapeutic activity of LC10 (MEDI4893*), an affinity-optimized version of 2A3 (13), was compared with those of two frontline antibiotics, vancomycin and linezolid, in the murine dermonecrosis model.…”

“…Alpha-toxin (AT), a 33-kDa cytolytic pore-forming toxin produced by a majority of S. aureus clinical isolates, has been reported to blunt this protective immune response. In a dermonecrosis model, it has been demonstrated that mice infected with S. aureus isogenic mutants defective for AT expression mount a robust inflammatory cytokine response (e.g., IL-1␤, keratinocyte chemoattractant [KC], IL-6, and IL-17) with accompanying immune cell infiltration, abscess formation, and significant disease attenuation compared to the case for mice infected with wild-type S. aureus (9,10). We reported similar results following prophylactic administration of the AT-neutralizing monoclonal antibody (MAb) 2A3, the MEDI4893* precursor (9).…”

“…In a dermonecrosis model, it has been demonstrated that mice infected with S. aureus isogenic mutants defective for AT expression mount a robust inflammatory cytokine response (e.g., IL-1␤, keratinocyte chemoattractant [KC], IL-6, and IL-17) with accompanying immune cell infiltration, abscess formation, and significant disease attenuation compared to the case for mice infected with wild-type S. aureus (9,10). We reported similar results following prophylactic administration of the AT-neutralizing monoclonal antibody (MAb) 2A3, the MEDI4893* precursor (9). Additionally, Fritz et al reported that patients with an S. aureus SSTI and high serum anti-AT IgG titers were less likely to have a recurrent infection than patients with low anti-AT titers, providing evidence for a role for AT in human disease (11).…”