CXCL1 regulates CD62L- and CD49d-dependent neutrophil mobilization in pneumococcal pneumonia-derived sepsis. (A-G) WT and Cxcl1^−/− mice were infected intratracheally with S pneumoniae 6303 (5 × 10⁴ CFU). Mice were euthanized at 48 hours postinfection. (A) Neutrophil (CD11b⁺Ly6G⁺) counts in bone marrow, blood, and lungs were measured. (B) Mean fluorescence intensity of CXCR4 on bone marrow neutrophil was measured. (C) Level of CXCL12 in bone marrow lysates. (D-E) Representative histograms and mean fluorescence intensities of the CD62L in neutrophils. (F-G) Representative histograms and mean fluorescence intensities of the CD49d in neutrophils. (H-I) WT and Cxcl1^−/− mice were infected intratracheally with S pneumoniae 6303 (5 × 10⁴ CFU). Mice were treated with L-selectin sheddase inhibitor (TAPI-O or KD-IX-73-4) or mAb against CD49d or vehicle control (dimethyl sulfoxide or IgG) i.p. at 0 and 24 hours postinfection and then euthanized at 48 hours postinfection. The total number of BM neutrophils (CD11b⁺Ly6G⁺) per femur/tibia (H) and the percentage of blood neutrophil (CD11b⁺Ly6G⁺) (I) were measured. (n = 5-6 mice/infection group; n = 3 mice/control group). All experiments were performed 3 times. Statistical significance was determined by unpaired Student t test (A-G) and 1-way ANOVA (followed by Bonferroni’s post hoc comparisons; H-I). *P < .05; **P < .01; ***P <.001.