Chemokine expression by Balb/c and C57Bl/6 mice following infection with PVM 15. Five to six week-old Balb/c and C57Bl/6 mice were inoculated with medium, 30 pfu, 300 pfu, or 3000 pfu of PVM 15 and lungs were collected from four mice per group on days 3 (A–D) and 5 p.i. (E–H). The expression levels of CXCL8 (A and E), CXCL10 (B and F), CCL3 (C and G), and CCL2 (D and H) were calculated using the Bio-Rad analysis software (Bio-Rad CFX Manager Version 2.0), normalized against the expression of both β-actin and GAPDH housekeeping genes, and expressed as the normalized fold-change over mock-infected control animals euthanized on the same day p.i.. Each data point represents a single animal and the line represents the group median. *, p <0.05.