TNF and cystic fibrosis: Although proinflammatory cytokines in sputum samples are useful markers of lung disease activity in CF patients, there is a large variability in TNF-α and IL-8 concentrations in relation to the clinical condition of patients, with peak values on days 3–6 during exacerbation, and a correlation with the colonization of Pseudomonas aeruginosa or Staphylococcus aureus in the lower airways [40].