In experiments where mice were first exposed to CB and then RSV, viral titers in RSV + CB mice were lower than RSV alone on days 2-4 of infection, and yet by day 7 of expsoure neutrophil numbers, proinflammatory cytokine mRNA expression, and protein levels of TNF-alpha and the Th2 cytokine interleukin (IL)-13 were increased in the lungs of RSV + CB mice, indicating an exacerbation of infection [26]. Here, IL13 is linked to infection.