Evaluating the Role of STAT3 in CD4(+) T Cells in Susceptibility to Invasive Aspergillosis

We aimed to determine whether T cell-specific STAT3 deletion influences the immune response to Aspergillus in the immunosuppressed context in CD4(Stat3)(−/−) mice. Immunosuppressed and nonimmunosuppressed CD4(Stat3)(−/−) mice and littermate Stat3(flox/flox) (Stat3(fl/fl)) mice were infected with Aspergillus fumigatus in an aerosol chamber, and the weight, activity, appearance, and respiratory rate of the mice were monitored daily for 21 days to evaluate their survival. Aspergillus infection was confirmed by lung fungal culture counts, histology, and a galactomannan test. Cytokines were measured at 3 days postinfection in bronchoalveolar lavage (BAL) fluid and serum. Immunosuppressed CD4(Stat3)(−/−) mice began succumbing to infection by day 4, and by day 7, only 30% of mice survived. Immunosuppressed Stat3(fl/fl) mice started to succumb to the disease on day 5, and 40% of mice remained by day 7. The nonimmunosuppressed control Stat3(fl/fl) and CD4(Stat3)(−/−) mice maintained their weight over the study period, without any evidence of infection by A. fumigatus by histology. In the BAL fluid, tumor necrosis factor alpha (TNF-α), interleukin-6 (IL-6), interferon gamma (IFN-γ), IL-17A, and IL-22 levels were elevated in Stat3(fl/fl) immunosuppressed mice compared to immunosuppressed CD4(Stat3)(−/−) mice at 3 days postinfection. STAT3 in CD4(+) T cells modulates the production of cytokines in the IL-17 pathway in immunosuppressed mice. However, it has no meaningful effect on the clearance of Aspergillus or the concomitant increase in susceptibility to Aspergillus infection.