Furthermore, a moderate increase in CTLA4 expression was also observed at first week post-infection (6 dpi) in both infected groups, which coincided with the peak of viral load in lung (virulent Lena strain) or tracheobronchial lymph node (low virulent 3249 strain) and correlated with the severity of lung lesion in both infected groups (ρ > 0.6). Here, CTLA4 is linked to infection.