CXCL9 and pneumonia: The greater expression of interferon-induced genes in S. pneumoniae infection was also reflected at the protein level as shown by the significantly higher amounts of interferon-induced CXCL9 (Figure 4A) and CXCL10 (Figure 4B) in serum of S. pneumonia-infected mice in comparison with S. aureus-infected or PBS-treated mice.