Aspergillus fumigatus–Induced IL-22 Is Not Restricted to a Specific Th Cell Subset and Is Dependent on Complement Receptor 3

Th cell responses induced by Aspergillus fumigatus have been extensively investigated in mouse models. However, the requirements for differentiation and the characteristics of A. fumigatus-induced human Th cell subsets remain poorly defined. We demonstrate that A. fumigatus induces Th1 and Th17 subsets in human PBMCs. Moreover, we show that the cytokine IL-22 is not restricted to a specific Th subset, in contrast to IL-17A. The pattern recognition and cytokine pathways that skew these Aspergillus-induced Th cell responses are TLR4- and IL-1-, IL-23-, and TNF-α-dependent. These pathways are of specific importance for production of the cytokines IL-17A and IL-22. Additionally, our data reveal that the dectin-1/Syk pathway is redundant and that TLR2 has an inhibitory effect on Aspergillus-induced IL-17A and IL-22 production. Notably, blocking complement receptor (CR)3 significantly reduced Aspergillus-induced Th1 and Th17 responses, and this was independent on the activation of the complement system. CR3 is a known receptor for β-1,3-glucan; however, blocking CR3 had significant effects on Th cell responses induced by heat-killed Aspergillus conidia, which have minimal β-glucan expression on their cell surface. Collectively, these data characterize the human Th cell subsets induced by Aspergillus, demonstrate that the capability to produce IL-22 is not restricted to a specific T cell subset, and provide evidence that CR3 might play a significant role in the adaptive host defense against Aspergillus, although the ligand and its action remain to be elucidated.