To investigate the basis for these differences, the levels of cytokines and chemokines in broncho-alveolar lavage (BAL) fluids were measured early (24 h) p.i. This showed that there were enhanced levels of IL-2, IL-6, TNF-α, CCL11, CXCL9 and CXCL10 following infection with vΔ169 compared to both control viruses, whereas the levels of CCL2, CCL9, IL-12 and IL-15 were unchanged (Fig 11B and 11C). This evidence concerns the gene IL15 and infection.