Influenza infections cause millions of hospitalizations globally each year, resulting in hundreds of thousands of deaths and exacting a large toll on the economy. Accordingly, new interventions are highly desired including the elusive universal influenza vaccine capable of providing long-lasting immunity to all strains of influenza, including those which have not yet circulated in humans. It is vital to determine factors which suppress immunity to influenza infection and worsen host outcomes during infection. The food additive, tert-butylhydroquinone (tBHQ), was shown by our lab to modulate CD4+ T cell activation and function in ex vivo analyses, in part by activating the stress-activated transcription factor, nuclear factor erythroid 2-related factor 2 (Nrf2). However, it was unknown if tBHQ hindered T cell function in vivo. To assess this, we fed mice diets with or without 0.0014% tBHQ and infected them with sublethal influenza A virus. Following primary infection, mice exposed to tBHQ had fewer CD8+ T cells in the lungs, and these cells displayed a phenotype consistent with reduced effector function. Notably, these findings correlated with augmented viral RNA levels in the lungs. Following secondary infection with a heterosubtypic strain of influenza virus, mice on tBHQ-containing diets had exacerbated weight loss and delayed recovery compared to mice on control diets, indicating that tBHQ impaired heterosubtypic memory responses. It was further revealed that splenic memory T cell populations were diminished 28 days following primary infection in mice on the tBHQ diet, suggesting failure to form a memory T cell population could be the cause for the diminished heterosubtypic immunity. To begin elucidating the molecular mechanism by which tBHQ suppressed the T cell response to influenza infection, two different models were utilized. The first model used adoptive transfer of wildtype or Nrf2-null T cells into T cell-deficient hosts prior to dietary exposure to tBHQ and infection with influenza virus. Interestingly, tBHQ had no effect on wildtype T cells in this model. However, this model demonstrated that Nrf2 in T cells contributes to influenza-associated morbidity, as mice with Nrf2-deficient T cells had reduced lung damage and ultimately lost less weight than their control counterparts. The other model exploited Cre/Lox technology to generate a conditional knockout mouse line with Nrf2-deficient T cells. In this model, the effects of tBHQ seen in wildtype mice during primary infection were shown to require Nrf2 in T cells. Additionally, this model also showed that mice with Nrf2-deficient T cells were protected from influenza-associated morbidity, though this only occurred in the presence of tBHQ. These studies collectively show that Nrf2 modulates the T cell response to influenza virus and contributes to host morbidity. Additionally, Nrf2 activation by tBHQ suppresses T cell responses to infection leading to failed memory responses. These are the first studies to investigate the role of tBHQ on T cellmediated immunity in vivo in addition to interrogating the role of Nrf2 in T cell responses to influenza virus infection.
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