We found that MMP-9 was highly up-regulated in the lungs of mice after intranasal challenge with S. pneumoniae. Furthermore, depletion of DCs resulted in significant reduction in the levels of MMP-9 in the infected lungs, which supports that DCs are either a direct source of MMP-9 during pneumococcal pneumonia or that they modulate MMP-9 production by other cell types. Here, MMP9 is linked to pneumococcal pneumonia.