For example, Robbins et al. (2006) exposed C57BL/6 mice for 3–5 months to mainstream tobacco smoke and then to influenza A and showed that smoke exposure caused suppression of inflammatory responses to low-dose influenza in bronchoalveolar lavage fluid (neutrophils, mononuclear cells) but no change for levels of cytokines IL-6, TNFα, or macrophage-inflammatory protein-2. Here, IL6 is linked to influenza.