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 1

Active IsdB immunization renders mice susceptible to sepsis following SSI.

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Active IsdB immunization renders mice susceptible to sepsis following SS...
(A) Anti-IsdB titers in sera of actively immunized and adjuvant control mice were determined by ELISA before transtibial implant surgery (n = 10 per group, ***P < 0.0001 via Mann-Whitney test, lower limit of detection <100). (B) Longitudinal BLI images, with heatmap signal intensities, of a representative IsdB actively immunized mouse, with evidence of MRSA dissemination from the surgical site region of interest (ROI, red circled region) to internal organs (red arrow). (C) BLI signal within the tibial ROI are shown for individual mice, with the mean for the group (*P < 0.05 on day 7 via exact Wilcoxon test with an adaptive Hochberg multiplicity adjustment). (D) The body weight of the mice actively immunized against IsdB protein, or adjuvant only control, was obtained on the indicated days before and after challenge. Note that IsdB-immunized mice did not gain weight after MRSA challenge (n = 10 per group, *P < 0.05 on day 14 via 2-way ANOVA). Images of liver abscess (E) and pale kidneys (F) in anti-IsdB mAb–treated mice. (G) CFUs on the tibial pin and in internal organs were determine on day 14 after infection. The incidence and mean level of CFUs on the implants in both groups were similar (lower limit of detection <50). CFUs in internal organs of control mice were not detected (N.D.), while IsdB-immunized mice display evidence of MRSA dissemination (n = 10 per group, *P < 0.05 via Fisher’s exact test, lower limit of detection <10).