Mucosal Administration of Flagellin Protects Mice from Streptococcus pneumoniae Lung Infection

Abstract

Streptococcus pneumoniae is a major cause of pneumonia in infants and the elderly. Innate defenses are essential to the control of pneumococcal infections, and deficient responses can trigger disease in susceptible individuals. Here we showed that flagellin can locally activate innate immunity and thereby increase the resistance to acute pneumonia. Flagellin mucosal treatment improved S. pneumoniae clearance in the lungs and promoted increased survival of infection. In addition, lung architecture was fully restored after the treatment of infected mice, indicating that flagellin allows the reestablishment of steady-state conditions. Using a flagellin mutant that is unable to signal through Toll-like receptor 5 (TLR5), we established that TLR5 signaling is essential for protection. In the respiratory tract, flagellin induced neutrophil infiltration into airways and upregulated the expression of genes coding for interleukin 6 (IL-6), tumor necrosis factor alpha (TNF-␣), CXCL1, CXCL2, and CCL20. Using depleting antibodies, we demonstrated that neutrophils are major effectors of protection. Further, we found that B-and T-cell-deficient SCID mice clear S. pneumoniae challenge to the same extent as immunocompetent animals, suggesting that these cell populations are not required for flagellin-induced protection. In conclusion, this study emphasizes that mucosal stimulation of innate immunity by a TLR not naturally engaged by S. pneumoniae can increase the potential to cure pneumococcal pneumonia.

Treatment with anti‐inflammatory drugs in community‐acquired pneumonia

“…In an animal model of pneumococcal pneumonia, triggering of TLR-5 with its ligand, flagellin, leads to substantially improved survival [73]. This indicates the importance of the immediate activation of the innate response in clearance of a pulmonary infection.…”

Sublingual Immunotherapy as an Alternative to Induce Protection Against Acute Respiratory Infections

“…Discard the supernatant and resuspend the pellet in the appropriate volume of sterile saline to obtain a suspension of 4x10 5 CFU/50 µl. This dose corresponds to the minimum bacterial dose of S. pneumoniae serotype 1 E1586 that causes 100% mortality in BALB/c mice according to previous studies 15 . NOTE: When establishing a model of pneumococcal pneumonia in mice, the minimum bacterial dose causing 100% of mortality must be determined for each particular combination of bacterial strain, serotype and mouse strain.…”

“…Apply vet ointment onto the eyes and return the animals to the cage; make sure to maintain normothermia while under anaesthesia. NOTE: In this study bacterial challenge was performed in a volume of 50 µl to ensure delivery of at least 90% of the total CFU into the lungs as determined previously in 15,28 . To minimize distress of the animal's smaller volumes (e.g., 20 µl) can be used.…”

“…Thaw an aliquot of a working stock suspension of Streptococcus pneumoniae of known bacterial CFU number prepared as described in 15 . 2.…”

“…When FliC is sensed by the PRRs an important inflammatory response is triggered. We and others have demonstrated that instillation of purified FliC from Salmonella enterica serovar Typhimurium into the lungs drives swift production of chemokines and cytokines specially when recognized by the lungs' epithelium that in turn orchestrate the recruitment of immune cells into the airways, mainly PMNs 15,[19][20][21] . Although transient, the substantial neutrophil infiltration that takes place into the airways after nasal delivery of FliC could be a concern if moving towards clinical therapies for human use.…”