Interleukin 1 enhances vaccine-induced antifungal T-helper 17 cells and resistance against blastomyces dermatitidis infection

Vaccine-induced T-helper 17 (Th17) cells are necessary and sufficient to protect against fungal infection. Although live fungal vaccines are efficient in driving protective Th17 responses and immunity, attenuated fungi may not be safe for human use. Heat-inactivated formulations and subunit vaccines are safer but less potent and require adjuvant to increase their efficacy. Here, we show that interleukin 1 (IL-1) enhances the capacity of weak vaccines to induce protection against lethal Blastomyces dermatitidis infection in mice and is far more effective than lipopolysaccharide. While IL-1 enhanced expansion and differentiation of fungus-specific T cells by direct action on those cells, cooperation with non-T cells expressing IL-1R1 was necessary to maximize protection. Mechanistically, IL-17 receptor signaling was required for the enhanced protection induced by IL-1. Thus, IL-1 enhances the efficacy of safe but inefficient vaccines against systemic fungal infection in part by increasing the expansion of CD4⁺ T cells, allowing their entry into the lungs, and inducing their differentiation to protective Th17 cells.