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A1002 - ILC2s and Eosinophils Protect Against Staphylococcus Aureus Induced Sepsis
Author Block: P. Krishack1, T. Louviere1, A. I. Sperling2, P. A. Verhoef3; 1Medicine, University of Chicago, Chicago, IL, United States, 2Medicine/PCCM, University of Chicago, Chicago, IL, United States, 3Univ of Chicago, Chicago, IL, United States.
Rationale: Sepsis is defined as life-threatening organ dysfunction caused by an inappropriate inflammatory response to infection. While this detrimental response remains poorly understood, we recently demonstrated that a pre-existing type 2 response protects against death induced by Staphylococcus aureus (S. aureus) bacteremia. However, the mechanism of this protection remains undetermined.
Methods: C57BL/6 mice were treated intratracheally with PBS or IL-33 for 3 days and intravenously infected with a lethal dose of USA300 S. aureus on day 4. The following day flow cytometry was used to quantify lung ILC2s, neutrophils and eosinophils. For survival analysis, mice were monitored for weight loss and survival. To investigate the role of specific cell types in survival, PLZF-/- mice (lacking functional type 2 innate lymphoid cells or ILC2, and lacking functional natural killer T cells, or NKT), CD1d-/- mice (lacking functional NKT) and Rag1-/- mice (lacking all T cells) were used. Inducible eosinophil depletion was achieved by treating iPHIL mice, which express the diphtheria toxin receptor exclusively on eosinophils, with diphtheria toxin prior to infection. For neutrophil depletion, mice were injected with Ly6G (1A8) antibody prior to infection.
Results: Mice pretreated with IL-33 prior to infection demonstrated an expanded number of ILC2s and type 2 cytokines compared with infected control mice. Infection of PLZF-/- mice, which lack functional ILC2 and NKT cells, resulted in accelerated mortality compared to wild type littermate controls. Moreover, IL-33 did not rescue PLZF-/- mice from death. However, infection of mice deficient in only NKT cells (CD1d-/-) or all T cells (Rag1-/-) demonstrated no difference in mortality compared to controls, likely because both strains retained functional ILC2s. Because ILC2 activation leads to eosinophil recruitment, we evaluated granulocyte subsets in the lungs and noted an increase in the ratio of lung eosinophils to neutrophils in IL-33 treated, S. aureus infected mice, compared to mice infected with S. aureus alone. This suggested that type 2 responses may protect by suppressing lung neutrophilia associated with infection. However, depletion of neutrophils after infection accelerated mortality, even in the presence of IL-33 pretreatment, arguing that some neutrophil function is necessary during sepsis. Remarkably, inducible depletion of eosinophils after infection abrogated IL-33 mediated protection, revealing a novel role for eosinophils in protecting against sepsis.
Conclusions: Type 2 innate immunity provided by ILC2-dependent eosinophilia is critical for protection against S. aureus-mediated death.