Sara van den Berg

103 4 CMV on influenza infection We next investigated whether CMV infection was associated with more severe symptoms during influenza virus infection compared to CMV- individuals. No significant differences between CMV- and CMV+ individuals were observed in the number of symptoms during influenza virus infection ( Figure 5B ), total duration of symptoms ( Figure 5C ), or severity of symptoms as assessed by a combination of duration and number of symptoms ( Figure 5D ). When investigating the influenza virus infection symptoms individually, CMV+ individuals did suffer less often from muscle pain ( Figure 5E) and although coughing was not different between CMV+ and CMV-, CMV+ tended to cough less long compared to CMV- individuals (data not shown). When the frequency of individuals coughing was plotted over time, we indeed found a faster decline in the frequency of coughing individuals amongst CMV+ individuals compared to CMV- individuals ( Figure 5F ). Of note, both the increased frequency of muscle pain and the longer persistence of coughing among CMV- individuals could not be ascribed to the difference in virus strain infection between CMV- and CMV+ individuals (data not shown). Together, this suggests that CMV infection does not worsen the number and duration of influenza virus infection symptoms, and may actually be slightly beneficial. DISCUSSION In this study we tested the role of CMV infection on the immune response to influenza virus infection at older age. We found that CMV infection induces a more differentiated and senescent phenotype in the CD8 + T-cell pool. Importantly, CMV+ older individuals had lower frequencies of influenza virus-specific CD8+ T-cells compared to CMV- older individuals. However, these lower frequencies of influenza virus-specific T-cells in CMV+ older individuals did not hamper the induction of a T-cell response during active influenza virus infection. Also, severity of influenza-associated symptoms was not negatively affected by CMV infection. Investigating two hypothesis of CMV-enhanced ageing, we did not find evidence supporting a negative effect of CMV infection in some CMV+ individuals by ‘limited immunological space’ or by presence of pro-inflammatory mediators. In contrast, a small positive association of CMV infection might be present, as T-cell responses against influenza were slightly increased in CMV+ individuals early after influenza virus infection (<72 hours after fever onset) and positively associated with the height of the CMV-specific T-cell response 2 weeks and 8 weeks after influenza virus infection. Pre-existing T-cells and timing of the influenza virus-specific CD8+ T-cell response are thought to play an important role in the reduction of severity of influenza-related symptoms [23, 24]. An early T-cell response is thought to reduce the level of inflammation and to accelerate viral clearance, whereas delayed and prolonged T-cell response leads to high and prolonged levels of inflammation and increased severity of disease [24, 25]. Unfortunately, pre-existing T-cell responses could not be investigated in this study. Our data suggest that CMV+ individuals have an increased early or accelerated influenza virus-specific T-cell response compared to CMV- individuals. We speculate that this may lead to earlier viral clearance, and thereby might explain the faster recovery of coughing and decreased frequency of muscle pain. When we assessed severity of symptoms by the number and