A Novel Innate Immune-Enhancement Strategy Combined with IVIG Rescues Mice from Fatal Staphylococcus aureus Septicemia

Abstract

Staphylococcus aureus (SA) is a major community-acquired pathogen. The emergence of drug-resistant strains like, methicillin-resistant SA (MRSA), poses stiff challenges to therapeutic intervention. Passive immune-therapy with specific antibodies is being actively examined to treat fulminant infections with limited success. In this study, we demonstrate that P4, a 28-amino acid peptide, derived from pneumococcal surface adhesin A along with pathogen-specific antibody (IVIG; P4 therapy) is successful in enhancing the opsonophagocytic killing (OPK) of S. aureus in vitro. We questioned if it is possible to expand P4 therapy to treat staphylococcal infections in vivo. P4 therapy in combination with IVIG rescued 7/10 morbidly ill S. aureus-infected mice while only 2/10 survived in the control group.

Figure 1

P4-mediated enhancement of in vitro opsonophagocytic killing of Staphylococcus aureus strainN. In vitro opsonophagocytosis killing assay was performed with HL60-cells-derived granulocytes. Addition of P4 increased the opsonophagocytic killing of S. aureus strainN in the presence of strain-specific antibodies. Maximum enhancement (≥70%) was seen with HM904 over control that had all OPKA components except P4 (P < 0.05). Antibodies used in this in vitro assay: Gamunex (IVIG), a pooled human serum having reactivity with a wide range of pathogens including S. aureus; ab35194, rabbit polyclonal directed towards the soluble and structural antigens of the S. aureus; PAbClfA, rabbit polyclonal IgG directed towards the clumping factor A, ClfA of S. aureus, and HM904, humanized mouse monoclonal anti-ClfA IgG.

Figure 2

P4-mediated enhancement of OPK of S. aureus strainN with fresh PMNs isolated from human blood. In vitro opsonophagocytosis killing assay was performed with human peripheral blood PMN's. Addition of P4 increased the opsonophagocytic killing of S. aureus strainN in the presence of strain-specific antibodies. Maximum enhancement (≥100%) was seen with HM904 over control that had all OPKA components except P4 (P < 0.05). Antibodies used in this in vitro assay: Gamunex (IVIG), a pooled human serum having reactivity with a wide range of pathogens including S. aureus; ab35194, rabbit polyclonal directed towards the soluble and structural antigens of the S. aureus; PAbClfA, rabbit polyclonal IgG directed towards the clumping factor A, ClfA of S. aureus, and HM904, humanized mouse monoclonal anti-ClfA IgG.

Figure 3

Survival of S. aureus-strainN-infected mice after P4-treatment. P4 with serotype-specific IgG confers protection to Swiss-Webster mice against intranasal S. aureus strainN challenge. Intravenous injection of P4 (100 μg/mouse) with Gammaglobulin (100 μL/mouse) at 15 and 24 hours after challenge provided highly significant protection (70%; P = 0.02) from S. aureus strainN infection (Kaplan-Meier analysis).