23.05 IL-33 DRIVES TYPE 2 CYTOKINES THROUGH ILC2 IN THE LUNGS AFTER HEMORRHAGIC SHOCK/TRAUMA (HS/T)

J. Xu¹, J. Guardado¹, R. Hoffman¹, H. R. Turnquist¹, T. R. Billiar^{1  1}UPMC,Surgery Department,Pittsburgh, PA, USA

Introduction: The immunosuppression/immune dysregulation that follows severe injury includes a strong bias towards type 2 immune responses. These responses, which are characterized by the production of the type 2 cytokines (IL-4, IL-5 and IL-13), are typically thought to be the result of polarization of CD4⁺ T cells towards a Th2 phenotype. However, polarization of naïve T cells can take several days while elevations of type 2 cytokine production is often detected early after injury. This lead us to hypothesize that IL-33, an alarmin released early after injury, and type II innate lymphoid cells (ILC2) , a recently described population of T cell receptor negative innate lymphocyte cells (most abundant in the lungs), contribute to the early type 2 immune responses after injury.

Methods:  IL-33, and the type 2 cytokines (IL-4, IL-5 and IL-13) levels were detected in the plasma of blunt trauma patients. C57BL/6, IL-33^-/- and ILC2 deficient mice were subjected to resuscitated hemorrhagic shock + bilateral lower extremity injury (HS/T), ILC2 percentage and activation were assessed by flow cytometry of lung leukocytes using IL-5 as a representative type 2 cytokine. Mice deficient in ILC2 were generated by reconstituting irradiated wild type (WT) with bone marrow from staggerer (Rora^sg/sg) mice.

Results: Severely injured human blunt trauma patients (n=493, average ISS=20.2) exhibited early elevations in plasma IL-33 which correlated positively with increases in IL-4, IL-5 and IL-13. In C57BL/6 mice, HS/T led to a significant increase in lung IL-5 (measured by flow), IL-33 (measured by ELISA) and ILC2 percentage (CD45⁺Lineage^–CD25⁺ CD127⁺CD90.2⁺ ST2⁺Sca-1⁺ CD117^int) in the lungs at 6 hrs (p<0.05, n=4 for each time point). IL-5⁺ ILC2 were easily identified in the lungs by 6hrs. However, the increases in both ILC2 percentage and ILC2 IL-5 expression were absent in IL-33^-/- mice subjected to HS/T (n=4/group). IL-5 could also be detected in PMN (Ly6G+CD11b+) in the lungs of injured mice but this was suppressed by IL-33^-/- or ILC2 deletion. Using cultured PMN, we confirmed that exogenous IL-5 could lead to the increase of PMN IL-5 expression, measured by both flow and PCR (n=4/group).

Conclusion: These data show that early IL-33 elevations correlate with type 2 cytokines levels in blunt trauma patients. Reverse translation experiments in mice establishes that IL-33 drives ILC2 activation and type 2 cytokine production in the lungs of injured mice within 6 hrs. Furthermore, ILC2 derived IL-5 appears to upregulate IL-5 in PMNs thus amplifying the local type 2 response.  Combined these data show that the shift towards type 2 responses occurs rapidly after injury involve innate lymphoid cells responding to IL-33.