Two-dimensional gel electrophoresis analysis in simultaneous influenza pneumonia and bacterial infection in mice

Animal models of polymicrobial pneumonia

Pneumonia is one of the leading causes of severe and occasionally life-threatening infections. The physiopathology of pneumonia has been extensively studied, providing information for the development of new treatments for this condition. In addition to in vitro research, animal models have been largely used in the field of pneumonia. Several models have been described and have provided a better understanding of pneumonia under different settings and with various pathogens. However, the concept of one pathogen leading to one infection has been challenged, and recent flu epidemics suggest that some pathogens exhibit highly virulent potential. Although "two hits" animal models have been used to study infectious diseases, few of these models have been described in pneumonia. Therefore the aims of this review were to provide an overview of the available literature in this field, to describe well-studied and uncommon pathogen associations, and to summarize the major insights obtained from this information.

Critical role of IL-1 receptor-associated kinase-M in regulating chemokine-dependent deleterious inflammation in murine influenza pneumonia

Influenza virus is a common cause of respiratory infection and morbidity, which is often due to deleterious host immune responses directed against the pathogen. We investigated the role of IL-1 receptor-associated kinase-M (IRAK-M), an inhibitor of MyD88-dependent TLR signaling, in modulating the innate inflammatory response during influenza pneumonia using a murine model. The intranasal administration of influenza resulted in the upregulation of IRAK-M mRNA and protein levels in the lungs within 2 d after infectious challenge. Pulmonary influenza infection in mice deficient in IRAK-M (IRAK-M(-/-)) resulted in substantially increased mortality compared with similarly treated wild-type animals. Increased mortality in IRAK-M(-/-) mice was associated with enhanced early influx of neutrophils, high permeability edema, apoptosis of lung epithelial cells, markedly increased expression of inflammatory cytokines/chemokines, and release of neutrophil-derived enzymes, including myeloperoxidase and neutrophil elastase. Early viral clearance was not different in mutant mice, whereas viral titers in lungs and blood were significantly higher in IRAK-M(-/-) mice compared with wild-type animals. Increased lethality observed in IRAK-M(-/-) mice after influenza challenge was abrogated by Ab-mediated blockade of CXCR2. Collectively, our findings indicate that IRAK-M is critical to preventing deleterious neutrophil-dependent lung injury during influenza infection of the respiratory tract.

A patient with fulminant influenza-related bacterial pneumonia due to Streptococcus pneumoniae followed by Mycobacterium tuberculosis infection

A 74-year-old man with poorly controlled diabetes mellitus was admitted to our hospital because of severe respiratory disturbance, fever, and sputum. We found massive consolidation of the right lung and nodular shadows on the left lung on chest X-ray, and detected influenza virus and Streptococcus pneumoniae antigen from a nasopharyngeal swab and urine sample, respectively. Co-infection with influenza virus and bacteria was suspected, and oseltamivir and biapenem were prescribed. Laboratory data improved after the addition of sivelestat sodium hydrate, an inhibitor of neutrophil-derived elastase; however, chest X-ray findings became worse on Day 8, and we administered 1 g methylprednisolone intravenously for two days. On Day 12, we detected Mycobacterium tuberculosis in the sputum, even though we did not previously detect any acid-fast bacilli, and started anti-tuberculosis drugs, such as isoniazid, rifampicin, ethambutol hydrochloride, and pyrazinamide; however, the patient died 12 days later. Severe influenza-related bacterial pneumonia with Streptococcus pneumoniae and subsequently secondary tuberculosis infection were finally suspected in this case. This was a very rare case in which additional tuberculosis infection was found in a patient with fulminant pneumonia due to co-infection of influenza virus and bacteria. It is necessary to observe patients with influenza carefully, especially when steroids are used, even if antibiotics are also administered.