CCL5 and viral infectious disease: We also noticed that the expression of Ccl5 and Il12a/Il12p70 reached the peak on 5 d.p.i., which could reflect the activation of T and natural killer (NK) cells during viral infection (p = 0.0050 for Ccl5 in C57BL/6, p < 0.0001 for Il12a/Il12p70 in BALB/c and C57BL/6).