IsdB antibody–mediated sepsis following S. aureus surgical site infection
Kohei Nishitani, Masahiro Ishikawa, Yugo Morita, Noriaki Yokogawa, Chao Xie, Karen L. de Mesy Bentley, Hiromu Ito, Stephen L. Kates, John L. Daiss, Edward M. Schwarz
Kohei Nishitani, Masahiro Ishikawa, Yugo Morita, Noriaki Yokogawa, Chao Xie, Karen L. de Mesy Bentley, Hiromu Ito, Stephen L. Kates, John L. Daiss, Edward M. Schwarz
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Research Article Bone biology Infectious disease

IsdB antibody–mediated sepsis following S. aureus surgical site infection

Abstract

Staphylococcus aureus is prevalent in surgical site infections (SSI) and leads to death in approximately 1% of patients. Phase IIB/III clinical trial results have demonstrated that vaccination against the iron-regulated surface determinant protein B (IsdB) is associated with an increased mortality rate in patients with SSI. Thus, we hypothesized that S. aureus induces nonneutralizing anti-IsdB antibodies, which facilitate bacterial entry into leukocytes to generate “Trojan horse” leukocytes that disseminate the pathogen. Since hemoglobin (Hb) is the primary target of IsdB, and abundant Hb-haptoglobin (Hb-Hp) complexes in bleeding surgical wounds are normally cleared via CD163-mediated endocytosis by macrophages, we investigated this mechanism in vitro and in vivo. Our results demonstrate that active and passive IsdB immunization of mice renders them susceptible to sepsis following SSI. We also found that a multimolecular complex containing S. aureus protein A–anti-IsdB–IsdB–Hb-Hp mediates CD163-dependent bacterial internalization of macrophages in vitro. Moreover, IsdB-immunized CD163–/– mice are resistant to sepsis following S. aureus SSI, as are normal healthy mice given anti-CD163–neutralizing antibodies. These genetic and biologic CD163 deficiencies did not exacerbate local infection. Thus, anti-IsdB antibodies are a risk factor for S. aureus sepsis following SSI, and disruption of the multimolecular complex and/or CD163 blockade may intervene.

Authors

Kohei Nishitani, Masahiro Ishikawa, Yugo Morita, Noriaki Yokogawa, Chao Xie, Karen L. de Mesy Bentley, Hiromu Ito, Stephen L. Kates, John L. Daiss, Edward M. Schwarz

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Figure 3

Anti-IsdB mAb passive immunization renders mice susceptible to sepsis following SSI.

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Anti-IsdB mAb passive immunization renders mice susceptible to sepsis fo...
(A) Mice were passively immunized with anti-IsdB or irrelevant control mAb (n = 9), challenged with a USA300LAX:Luc-contaminated transtibial implant, and longitudinal BLI was performed as described in Methods. The BLI signal within the tibial ROI for individual mice on the indicated day after challenge is presented with the mean for the group (*P < 0.05 on day 3, **P < 0.01 on days 1 and 10 via exact Wilcoxon test with an adaptive Hochberg multiplicity adjustment). (B) CFUs on the tibial pin and in internal organs were determine on day 14 after infection of passively immunized mice. The incidence and mean level of CFUs on the implants in both groups were similar (lower limit of detection <10). However, CFUs in internal organs of control mAb-treated mice were not detected (N.D.), while anti-IsdB mAb–treated mice displayed evidence of MRSA dissemination (n = 9, *P < 0.05 via Fisher’s exact test, lower limit of detection <10). (C) Longitudinal BLI images with heatmap signal intensities of a representative mouse passively immunized with IsdB with evidence of MRSA dissemination from the surgical site (red circled region) to internal organs (red arrow). (D–G) Gross anatomy and renal histology of internal organs from mice passively immunized with control IgG and anti-IsdB mAb, illustrating the normal versus pale kidneys (white arrows) and evidence of renal tubular necrosis (black arrow) in anti-IsdB–treated mice. Scale bar: 20 μm.