CXCL1 and infection: Similarly, neutrophil clusters were nearly absent in the lungs of WT mice infected with the small bacterium S. pneumonia 24 hr after infection but potent clustering was elicited in Cybb-deficient animals (Figure 4D) along with elevated IL-1β, CXCL1, and CXCL2 expression without a significant increase in bacterial burden (Figures 4D, right, and S5E).