Complement Receptor 3 and Toll-Like Receptor 4 Act Sequentially in Uptake and Intracellular Killing of UnopsonizedSalmonella entericaSerovar Typhimurium by Human Neutrophils

Abstract

The uptake and subsequent killing of Salmonella enterica serovar Typhimurium by human neutrophils was studied. In particular, two pattern recognition receptors, complement receptor 3 (CR3) and Toll-like receptor 4 (TLR4), were found to be essential for the efficient uptake and activation, respectively, of the NADPH oxidase. The uptake of Salmonella was almost completely inhibited by various monoclonal antibodies against CR3, and neutrophils from a patient with leukocyte adhesion deficiency type 1, which lack CR3, showed almost no uptake of Salmonella. A lipopolysaccharide (LPS) mutant strain of Salmonella was used to show that the expression of full-length, wild-type, or so-called smooth LPS is important for the efficient killing of intracellular Salmonella. Infection with wild-type-LPS-expressing Salmonella resulted in the generation of reactive oxygen species (ROS) in TLR4-decorated, Salmonella-containing vacuoles, whereas ROS were not induced by an LPS mutant strain. In addition, the recognition of Salmonella by neutrophils, leading to ROS production, was shown to be intracellular, as determined by priming experiments with intact bacteria under conditions where the bacterium is not taken up. Finally, the generation of ROS in the wild-type-Salmonella-infected neutrophils was largely inhibited by the action of a TLR4-blocking, cell-permeable peptide, showing that signaling by this receptor from the Salmonella-containing vacuole is essential for the activation of the NADPH oxidase. In sum, our data identify the sequential recognition of unopsonized Salmonella strains by CR3 and TLR4 as essential events in the efficient uptake and killing of this intracellular pathogen.

Candidate inhibitors of porcine complement

“…Importantly, this also indicate the rational for inhibition of these upstream effector systems The possible crosstalk in these findings were interesting in the light of the findings by van Bruggen et al, where CR3 was shown to be essential for uptake of the Gram-negative bacteria Salmonella enterica and LPS-signaling via TLR4 was essential for the subsequent killing of the bacteria via production of ROS by the NADPH oxidase in the phagosome (194).…”

Pattern Recognition Receptors and Their Role in Innate Immunity: Focus on Microbial Protein Ligands

“…It has been reported to interact with yeast zymosan, and to mediate non-opsonic binding and phagocytosis of several bacterial species including M. tuberculosis, Pseudomonas aeruginosa, Bordetella pertussis, Coxiella burnetii and Salmonella typhimurium [19,70]. In M. tuberculosis, two ligands for CR3 have been described.…”

Subversion of Innate Immunity by Periodontopathic Bacteria via Exploitation of Complement Receptor-3

“…A recent report has presented evidence suggesting that CR3 and TLR4 cooperate for the uptake and intracellular killing of Salmonella enterica serovar Typhimurium (van Bruggen et al, 2007). Although this was shown in neutrophils, rather than in macrophages, it could be speculated that CR3 may be exploited in a contextual way, i.e., dependent upon which TLR is predominantly activated by the pathogen.…”