Host defence duringKlebsiellapneumonia relies on haematopoietic-expressed Toll-like receptors 4 and 2

Abstract

In this study, the relative roles of Toll-like receptor (TLR)2 and TLR4 were investigated independently and together. Moreover, we studied the role of haematopoietic compartment in anti-Klebsiella host defence.We infected TLR2 and TLR4 single-, and TLR264 double knockout (KO) animals with different doses of Klebsiella pneumoniae. In addition, bone marrow chimeric mice were created and infected.TLR4 played a more prominent role in antibacterial defence than TLR2, considering that only TLR4 KO mice demonstrated enhanced bacterial growth in lungs and spleen 24 h after infection with 3610 3 colony-forming units of Klebsiella compared with wild-type (WT) mice. In late-stage infection or after exposure to a higher infectious dose, bacterial counts in lungs of TLR2 KO animals were elevated compared with WT mice and TLR264 KO animals were more susceptible to infection than TLR4 KO mice. TLR signalling in cells of haematopoietic origin is of primary importance in host defence against K. pneumoniae. These data suggest that: 1) TLR4 drives the antibacterial host response after induction of pneumonia with relatively low Klebsiella doses; 2) TLR2 becomes involved at a later phase of the infection and/or upon exposure to higher bacterial burdens; and 3) haematopoietic TLR2 and TLR4 are important for an adequate host response during Klebsiella pneumonia.

Anti-LPS antibodies protect against Klebsiella pneumoniae by empowering neutrophil-mediated clearance without neutralizing TLR4

“…These pathways are required for the host to sense a bacterial pathogen and to mount a protective immune response (34)(35)(36). In fact, TLR4-knockout mice, which lack the ability to respond to LPS, exhibit a defect in clearing multiple Gram-negative pathogens, including K. pneumoniae (37)(38)(39). Unlike the knockout mice, neutralization of LPS with 54H7 did not reduce animal survival or increase bacterial burden as compared with c-IgG, despite reducing levels of proinflammatory cytokines in the lung.…”

Immunological Variation Between Inbred Laboratory Mouse Strains

“…124,140 As a general rule, Tlr4 mutant mice are more susceptible to gram-negative infections, such as Klebsiella pneumonia. 174 Among the more common laboratory mouse strains, only C3H/HeJ has a point mutation in the Tlr4 gene that renders it unresponsive to LPS. A less common strain, C57BL10/ScCr, has a different null mutation of Tlr4.…”

Kinase Activity Profiling of Gram-Negative Pneumonia

“…Both CFU counts and cytokine/chemokine levels increased rapidly in time. Notably, this infectious dose results in approximately 80% lethality, starting from 48 h after infection (11,14). Hence, this model represents severe pneumonia, and samples were obtained from shortly after infection until shortly before the first deaths occurred.…”

“…Bacterial pneumonia was induced as described previously (11,14). K. pneumoniae serotype 2 (ATCC 43816) were grown in Tryptic Soy broth (Difco, Detroit, MI, USA) to midlogarithmic phase at 37°C.…”

“…NOD-like receptors (NLRs) may interact with DNA (AIM2) (9), peptidoglycan (NOD2, NALP1/3) and flagellin (IPAF) (9,10). Multiple PRRs detect their respective PAMPs simultaneously and interplay between pathways is highly likely to arise during an evolving infection (7,11).…”