Sara van den Berg

99 4 CMV on influenza infection T-cell response to influenza virus infection in older adults is not impaired by CMV, but increased in the early phase To investigate whether the T-cell response during influenza virus infection is influenced by CMV infection, we analyzed CMV+ and CMV- individuals separately. No significant effect of CMV-seropositivity on influenza virus-specific CD8 + T-cell percentages or on the percentage of T EM cells among the influenza virus-specific T-cells was observed ( Figure 2D,E ). Likewise, influenza virus-specific IFN γ responses were not negatively associated with CMV-seropositivity ( Figure 2F ) or with CMV-specific antibody levels in CMV+ individuals at any of the time points investigated ( Supplementary Figure 2B ). Surprisingly, in the acute phase (<72 hours after fever onset), CMV+ individuals even showed a significantly higher influenza virus-specific IFN γ T-cell response than CMV- individuals ( Figure 2F ), also when corrected for the percentage of T-cells among all lymphocytes a trend was observed ( Supplementary Figure 2A, right panel). Of note, this increased influenza T-cell responses in CMV+ individuals could not be explained by the moment of sampling within the 72 hours after fever onset (data not shown). Large CMV-specific T-cell responses are not associated with impaired influenza virus-specific T-cell responses As CMV might only affect the immune system in individuals with large CMV-specific T-cell responses, we next investigated the association between CMV infection and the T-cell response to influenza by taking into account the magnitude of the IFN γ CMV-specific T-cell responses within CMV+ individuals. No negative correlation between expanded CMV-specific T-cell responses and the height of the IFN γ T-cell response to influenza virus infection was observed at any of the three time points ( Figure 3A ). Surprisingly, we even observed a significant positive correlation between the height of the CMV-specific IFN γ T-cell response and the height of the influenza virus-specific IFN γ T-cell response at 2 and 8 weeks after fever onset ( Figure 3A ) (R: 0.52, p=0.016 and R:0.45, p=0.014 respectively). This argues against a competition between CMV-specific memory T-cells and influenza virus-specific T-cells during influenza virus infection. Cytokine levels in serum of influenza-infected individuals are not affected by CMV and not associated with influenza virus-specific T-cell responses We also investigated whether pro-inflammatory mediators may be associated with a negative impact of CMV infection on an immune response to a heterologous infection . Therefore, we investigated the levels of pro-inflammatory cytokines in serum of CMV+ and CMV- individuals, and their potential association with the influenza-specific T-cell response. At the early phase of infection, the inflammation-associated factors IL-6 and CRP were elevated in serum compared to 2 and 8 weeks later ( Figure 4A ). No significant difference in IL-6 and CRP levels was observed between CMV+ and CMV- individuals ( Figure 4A ). Also at the peak of the T-cell response (2 weeks later) and at steady state (week 8 after fever onset), CMV- and CMV+ individuals showed comparable cytokine profiles ( Figure 4A ). As it was suggested that a shift in the IFN γ :IL-10 ratio leads to a decline in influenza T-cell responses