To study the impact of MRP14 deficiency on cytokine release in gram-negative pneumonia, we measured the levels of cytokines (TNF-α, IL-1β, IL-6, IL-10) and chemokines (MIP-2, KC) in lung homogenates and plasma (TNF-α, IL-1β and IL-6 only) harvested from mrp14−/− and Wt mice after intranasal infection with Klebsiella. Surprisingly, overall differences between mouse strains were limited. Here, S100A9 is linked to bacterial pneumonia.