Abstract
Yersinia pestis, a Gram-negative bacterium that causes bubonic and pneumonic plague, is able to rapidly disseminate to other parts of its mammalian hosts. Y. pestis expresses plasminogen activator (PLA) on its surface, which has been suggested to play a role in bacterial dissemination. It has been speculated that Y. pestis hijacks antigen-presenting cells, such as macrophages (MPhis) and dendritic cells, to be delivered to lymph nodes to initiate dissemination and infection. Both alveolar MPhis and pulmonary dendritic cells express a C-type lectin receptor, DEC-205 (CD205), which mediates antigen uptake and presentation. However, no ligand has been identified for DEC-205. In this study, we show that the invasion of alveolar MPhisby Y. pestis depends both in vitro and in vivo on the expression of PLA. DEC-205-expressing MPhis and transfectants, but not their negative counterparts, phagocytosed PLA-expressing Y. pestis and Escherichia coli K12 more efficiently than PLA-negative controls. The interactions between PLA-expressing bacteria and DEC-205-expressing transfectants or alveolar MPhis could be inhibited by an anti-DEC-205 antibody. Importantly, the blockage of the PLA-DEC-205 interaction reduced the dissemination of Y. pestis in mice. In conclusion, murine DEC-205 is a receptor for PLA of Y. pestis, and this host-pathogen interaction appears to play a key role in promoting bacterial dissemination.
Highlights
Yersinia pestis, a Gram-negative bacterium that causes bubonic and pneumonic plague, is able to rapidly disseminate to other parts of its mammalian hosts
Two corresponding E. coli K12 strains CS180 and CS1861 (CS180 expressing an O-antigen, smooth) were used as controls. We have used these sets of strains to demonstrate that exposure of the core-LPS of E. coli and Y. pestis is essential to initiate the interaction of core-LPS and DC-SIGN/SIGN-R1 [19, 20, 47, 50]4 (Table 1)
Interactions of CHO-DEC-205 and Alveolar Macrophages with plasminogen activator (PLA)-expressing Y. pestis and E. coli Is Inhibited by DEC-205 Antibody—To verify the specificity of the Y. ing pPCP plasmid), and KIM10Ϫ, were examined for their ability to interact with interaction of PLA-expressing Y. pestis KIM10Ϫ-⌬ail and E. coli
Summary
Bacterial Strains—Escherichia coli K12 strain CS180 contains core LPS but lacks O-antigen [33]. The number of associated bacteria (adherent and internalized) per cell was quantified by washing the cells three times with RPMI medium containing 2% FCS and plating the culture after the cells were lysed by the addition of 0.5% saponin (Calbiochem). 1 ϫ 105 mouse cells were seeded into each well of 96-well plates, containing RPMI medium with 2% FCS and gentamicin at a concentration of 100 g/ml and were incubated for 1.5 h to allow the M⌽s to adhere to plates and kill the extracellular bacteria. Each well was washed three times with RPMI medium containing 2% FCS to remove nonadherent cells and lysed with saponin, following the same procedures as used in the in vitro phagocytosis assays. 1) 30 min before inoculation, mice were injected with ampicillin at a final concentration of 50 g/g of mouse body weight to maintain the plasmid-based expression of O-antigen in KIM6ϩ-Oϩ and PLA in KIM10ϩPLA. The rationale for the high dose of bacteria (ϳ109/ml) in the inoculum is discussed in depth under “Discussion.” 2) To meet biosafety and regulatory requirements, the tetracycline marker on the original pBR322 has been deleted. 3) The Y. pestis strains used in this study were cultured at 26 °C; at this temperature, Y. pestis does not produce the F1 capsule, which is capable of blocking interactions with host cells [15, 16, 20]
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