Daan Pieren

155 Regulatory KIR+RA+ CD8+ T cells accumulate with age Blood samples from older adults suffering from a common respiratory virus infection (62-83 years of age, n=36) were analyzed at the acute phase (0) (within two days of fever onset), and during follow-up at +2 and +8 weeks. Healthy asymptomatic individuals (61-82 years of age, n=8) from the same cohort were used as control samples. ( A ) Frequency of KIR + RA + T cells amongst the CD8 + T-cell population at the three time points in older adults infected with a seasonal coronavirus (n=5), influenza B virus (n=5), Rhinovirus (n=5), human metapneumovirus (hMPV) (n=4), or respiratory syncytial virus (RSV) (n=2). ( B ) Flow cytometry plots showing the proportion of CD69 + cells in KIR + RA + T cells in influenza A infected older adults at each of the indicated points in time. ( C ) Flow cytometry plots of the proportion of CD69 + cells within each of the indicated CD8 + T-cell subsets. ( D ) Bar graph indicates the symptom duration in days monitored in Influenza-A infected older adults (n=15) from which the symptom score was calculated. Statistical significance of data presented in bar graphs (mean ± s.d.) ( A ) was determined using row-matched one-way ANOVA (with Geisser- Greenhouse correction and Dunnett’s post-test) for the difference between the time points and Mann-Whitney U test was used to determine the difference between infected and asymptomatic healthy individuals. (The exact p -value is shown or ns=not significant.) 5