Neutrophil infiltration: comparison of strains and species at 48 hours and dynamics over 96 hours. A) Neutrophils in the nasal epithelium from rats inoculated 48 hours earlier with 104 cfu of bacteria from a single species (Rm154, TIGR4 and Poland(6b)-20) or from rats inoculated 96 hours earlier with 106 cfu of H. influenzae and 48 hours earlier with 104 cfu of Poland(6b)-20 were quantified using the MPO assay. Lines indicate median MPO values. P-value is calculated by the Wilcoxon rank sum test. B) Dynamics of neutrophil infiltration in response to nasal colonization by S. pneumoniae (TIGR4) or H. influenzae. Following inoculation groups of 5-8 rats were sacrificed and neutrophil infiltration was measured by MPO assay. Median MPO Units are plotted. Error bars represent SE. Dashed line represents median MPO of uninoculated rats.