As HMGB1 levels in sputum of patients with COPD13, asthma14, and cystic fibrosis15, and HMGB1 levels in bronchoalveolar lavage of patients with L. pneumophila pneumonia16, have been linked to disease severity28, we hypothesised that the level of HMGB1 in sputum would be related to pneumonia severity. This evidence concerns the gene HMGB1 and pneumonia.