Proinflammatory cytokine levels in the lung are reduced after heterosubtypic challenge in mice exposed to HDM following PR8 infection and positively correlate with increased viral load. (A) Schematic of the experimental timeline for data in B. (B) Quantification of Ifng, Il6, and Tnf transcript expression in whole lung tissue on experimental day 55 as measured by qRT-PCR. Data are pooled from 1–12 mice per group from five independent experiments. (C) Correlation of viral transcript expression and Ifng expression in whole lung tissue, Il6 expression in whole lung tissue, and level of T-bet expression in NP-specific CD4⁺ T cells isolated from the lung on experimental day 55. *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001. Graphs in B show mean ± SD. Data in B were analyzed by Mann–Whitney test, data in C were analyzed by Spearman’s rank correlation. pfu, plaque-forming units. IAV, influenza A virus; o.p., oropharyngeal. gMFI, geometric mean fluorescence intensity.