engleski

The early immune response in Legionella longbeachae serogroup 1 mice infection

Legionella longbeachae serogroup 1 is an important human pathogen responsible for almost half of all cases of legionelosis in Australia. The primary transmission mode of this microorganism is inhalation of dust from contaminated compost or soil. It was shown recently that, in comparison to other Legionella spp., L. longbeachae has an unusual high lethality potential with LD90 of only 105 cfu and causes, in contrast to classic Legionnaires’ disease, a unique focal bronchopneumonia, with a massive recruitment of inflammatory cells in the lungs. In the present study we characterised the cell infiltrate in the lungs, as well as the cytokine profiles in the sera and lungs of infected mice. C57Bl/6 mice were intratracheally inoculated with 105 cfu of L. longbeachae serogroup 1. For immunohistological procedures the lungs were fixed in formalin, dehydrated and embedded in paraffin. Sections were stained either with HE or labelled with different monoclonal antibodies (anti-CD11b, anti GR-1, anti-CD4, anti-CD8, anti-B220). The lungs were digested by collagenase/DNase and leukocytes were separated using a percoll gradient. The cells were phenotypied using monoclonal antibodies specific for the following leukocyte surface antigens: anti-CD11b, anti-GR-1. Three colour immunofluorescence analysis was performed by BD FACS Calibur™ flow cytometer using CellQuest™ software. 72 hours after infection levels of IFN-gamma, TNF-alpha and IL-12 in the sera and lungs were determined by enzyme immunoassays. Immunohistological staining showed an infiltration of CD11b+ and GR1+ cells in the peribronchial and perivascular areas of the lungs at an early phase of infection followed by infiltration of CD8+, CD4+ and B220+ cells. CD11b+ cells were predominant in the cell infiltrate and three cell subpopulations could be distinguished: CD11b+dim/GR-1- CD11b+bright/GR-1- and CD11b+bright/GR-1+ cells. The cytokine profiles in the lungs and sera of infected mice demonstrated a strong Th1 response, characterized by an increase of IFN-gamma, IL-12 and TNF-alfa. CD11b+/GR-1+ neutrophils are predominant cells in the early immune response to L. longbeachae infection accompanied by a strong Th1 cytokine profile.

legionellosis; inflammatory cells; cytokines

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