The neutrophil antimicrobial peptide cathelicidin promotes Th17 differentiation

The host defence peptide cathelicidin (LL-37 in humans, mCRAMP in mice) is released from neutrophils by de-granulation, NETosis and necrotic death; it has potent anti-pathogen activity as well as being a broad immunomodulator. Here we report that cathelicidin is a powerful Th17 potentiator which enhances aryl hydrocarbon receptor (AHR) and ROR gamma t expression, in a TGF-beta 1-dependent manner. In the presence of TGF-beta 1, cathelicidin enhanced SMAD2/3 and STAT3 phosphorylation, and profoundly suppressed IL-2 and T-bet, directing T cells away from Th1 and into a Th17 phenotype. Strikingly, Th17, but not Th1, cells were protected from apoptosis by cathelicidin. We show that cathelicidin is released by neutrophils in mouse lymph nodes and that cathelicidin-deficient mice display suppressed Th17 responses during inflammation, but not at steady state. We propose that the neutrophil cathelicidin is required for maximal Th17 differentiation, and that this is one method by which early neutrophilia directs subsequent adaptive immune responses. Neutrophils secrete numerous immune effector molecules including cathelicidin which is associated with antimicrobial properties. Here the authors implicate neutrophil derived cathelicidin in modulation of CD4 T cell homoeostasis and the promotion of Th17 CD4 T cells.

Automated summary

The host defence peptide cathelicidin is a potent Th17 potentiator, enhancing aryl hydrocarbon receptor and ROR gamma t expression in a TGF-beta 1-dependent manner, directing T cells towards Th17 phenotype while protecting them from apoptosis. Neutrophils secrete cathelicidin, which is required for maximum Th17 differentiation and plays a role in early neutrophilia directing subsequent adaptive immune responses.