The dysregulated, unbalanced immune response of sepsis results in a mortality exceeding 20%, yet recent findings by our group indicate that patients with allergic, type 2-mediated immune diseases are protected from developing sepsis. We evaluated CD4+ T helper (Th) cell polarization among patients with Staphylococcus aureus bacteremia and confirmed that survivors had a higher percentage of circulating Th2 cells, but lower frequencies of Th17 cells and neutrophils early in the course of infection. To establish the mechanism of this protection, we employed a mouse model of lethal S. aureus bacteremia and found that intratracheal pretreatment with the type 2-initiating cytokine IL-33 activated pulmonary type 2 innate lymphocytes (ILC2s) and promoted eosinophilia. In addition, stimulation of type 2 immunity prior to lethal infection suppressed the pulmonary neutrophilic response to S. aureus. Mice lacking functional ILC2s did not respond to IL-33 and were not protected from lethal bacteremia, but treatment of these mice with the type 2 cytokines IL-5 and IL-13 rescued them from death. Depletion of eosinophils abrogated IL-33-mediated protection, indicating that eosinophilia is also necessary for the survival benefit. Thus, we have identified a novel mechanism by which type 2 immunity can balance dysregulated septic inflammatory responses, thereby clarifying the protective benefit of type 2 immune diseases on sepsis mortality.
Paulette A. Krishack, Tyler J. Louviere, Trevor S. Decker, Timothy G. Kuzel, Jared A. Greenberg, Daniel F. Camacho, Cara L. Hrusch, Anne I. Sperling, Philip A. Verhoef