Effect of rLcrV and rYopB from Yersinia pestis on murine peritoneal macrophages in vitro

Susceptibility to Yersinia pseudotuberculosis infection is linked to the pattern of macrophage activation

T helper 1 cells play a crucial role in the clearance of Yersinia pseudotuberculosis infection. By producing cytokines and presenting antigens to T cells, activated macrophages can orientate the adaptive immune response. The pathway used by macrophages to metabolize arginine has been employed as an important parameter to discriminate their activation state. In this study, the pattern of macrophage activation in Y. pseudotuberculosis-infected BALB/c (Yersinia-susceptible) and C57BL/6 (Yersinia-resistant) mice and their immunostimulatory capacity were analysed. In the early phase of infection, macrophages obtained from C57BL/6 mice produced higher levels of NO, lower arginase activity, and larger amounts of IL-12 and TNF-alpha than macrophages from BALB/c mice. On the other hand, macrophages derived from BALB/c mice produced higher levels of IL-10 and TGF-beta than C57BL/6 mice. The Y. pseudotuberculosis infection leads to a fall in the macrophage immunostimulatory capacity of both strains of mice, with T-cell proliferation significantly reduced 12 h after infection. Moreover, we observed in the supernatant of co-culture of macrophages from infected mice with T lymphocytes from heat-killed Yersinia-immunized mice lower IFN-gamma production by cells from BALB/c mice than by C57BL/6 mice, and IL-4 was produced only by BALB/c mice on the first- and third-day post-infection. These results suggest that the pattern of macrophage activation is associated with susceptibility and resistance to Y. pseudotuberculosis infection in BALB/c and C57BL/6 mice.

Plant-derived recombinant F1, V, and F1-V fusion antigens of Yersinia pestis activate human cells of the innate and adaptive immune system

Plague is still endemic in different regions of the world. Current vaccines raise concern for their side effects and limited protection, highlighting the need for an efficacious and rapidly producible vaccine. F1 and V antigens of Yersinia pestis, and F1-V fusion protein produced in Nicotiana benthamiana administered to guinea pigs resulted in immunity and protection against an aerosol challenge of virulent Y. pestis. We examined the effects of plant-derived F1, V, and F1-V on human cells of the innate immunity. F1, V, and F1-V proteins engaged TLR2 signalling and activated IL-6 and CXCL-8 production by monocytes, without affecting the expression of TNF-alpha, IL-12, IL-10, IL-1beta, and CXCL10. Native F1 antigen and recombinant plant-derived F1 (rF1) and rF1-V all induced similar specific T-cell responses, as shown by their recognition by T-cells from subjects who recovered from Y. pestis infection. Native F1 and rF1 were equally well recognized by serum antibodies of Y. pestis-primed donors, whereas serological reactivity to rF1-V hybrid was lower, and that to rV was virtually absent. In conclusion, plant-derived F1, V, and F1-V antigens are weakly reactogenic for human monocytes and elicit cell-mediated and humoral responses similar to those raised by Y. pestis infection.

Early interaction of Yersinia pestis with APCs in the lung

Despite the importance of pneumonic plague, little is known of the early pulmonary immune responses that occur following inhalation of Yersinia pestis. Therefore, we conducted studies to identify the early target cells for uptake of Y. pestis in the lungs following intratracheal or i.v. inoculation. Following intratracheal inoculation, Y. pestis was rapidly internalized primarily by a distinctive population of CD11c+DEC-205+CD11b- cells in the airways, whereas i.v. inoculation resulted in uptake primarily by CD11b+CD11c- macrophages and granulocytes in lung tissues. The airway cells internalized and were infected by Y. pestis, but did not support active replication of the organism. Intratracheal inoculation of Y. pestis resulted in rapid activation of airway CD11c+ cells, followed within 24 h by the selective disappearance of these cells from the airways and lungs and the accumulation of apoptotic CD11c+ cells in draining lymph nodes. When CD11c+ cells in the airways were depleted using liposomal clodronate before infection, this resulted in a significantly increased replication of Y. pestis in the lungs and dissemination to the spleen and draining lymph nodes. These findings suggest that CD11c+ cells in the airways play an important role in suppressing the initial replication and dissemination of inhaled Y. pestis, although these results will also require confirmation using fully virulent strains of Y. pestis. Depletion of these airway cells by Y. pestis may therefore be one strategy the organism uses to overcome pulmonary defenses following inhalation of the organism.

Phosphorylation of p42/44 MAP kinase is required for rF1-induced activation of murine peritoneal macrophages

The Fraction 1 (F1) antigen of Yersinia pestis is known to induce thymocyte proliferation. It serves as a major protective antigen against challenge of Y. pestis. Recently, we reported rF1-induced activation of macrophages. Current investigation elucidates the role of p42/44 mitogen-activated protein kinases (MAPK)-mediated signal transduction in murine peritoneal macrophages on stimulation with rF1 (10 microg/ml) in vitro. The p42/44 MAPK activation was determined by studying the expression of the phosphorylated p42/44 MAPK in rF1-treated macrophages. PD98059, a specific inhibitor of MAPK kinase (MEK) inhibited the p42/44 MAPK phosphorylation, indicating the specificity of the above response. Furthermore, the rF1-induced phosphorylation of p42/44 MAPK is found to blocked by upstream protein kinase C inhibitor H7, tyrosine kinase inhibitor genistein and phosphoinositol-3-kinase (PI3-K) inhibitor wortmannin. Additionally, phosphorylation of JNK and activation of the transcription factor, c-jun and c-fos was also observed in response to rF1 treatment. The rF1-induced activation of p42/44 MAPK was correlated to the functional activation of macrophages by demonstrating the inhibition of actin rearrangement, IL-1, TNF-alpha and NO production caused by PD98059 in the rF1-treated macrophages.

Yersinia rLcrV and rYopB inhibits the activation of murine peritoneal macrophages in vitro

Yersinia antigenic proteins LcrV and YopB are translocators of effector Yops in type III secretion system. Recently, we have reported that rLcrV and rYopB inhibit the production of TNF-alpha, IFN-gamma, and IL-12 in murine peritoneal macrophages. It was also demonstrated that IL-10 and TLR2 signaling pathways and inhibition of MAPK cascade is involved in rLcrV- and rYopB-induced immunomodulation. In the present study, it is reported that rLcrV and rYopB inhibited the LPS-induced production of IL-1beta in macrophages. Pretreatment of macrophages with rLcrV and rYopB also inhibited the LPS-induced transcription of IL-6 but not of GM-CSF. However, the transcription of chemokines like MCP-1, MIP-1alpha, MIP-1beta, and RANTES were inhibited by rLcrV and rYopB. Both proteins also affected the cytoskeleton and lipid rafts in macrophages. It is further observed that IL-10 antibodies abrogated the rLcrV- and rYopB-induced inhibition of IL-1beta production in LPS-treated macrophages. The data, therefore, suggests a possible role of IL-10 in rLcrV and rYopB mediated inhibition of LPS-induced production of IL-1beta in macrophages.

Involvement of c-Jun N-Terminal Kinase in rF1 Mediated Activation of Murine Peritoneal Macrophages In Vitro

Fraction 1 (F1) protein forms a capsule on the surface of Yersinia pestis. Recently, we reported rF1-induced activation of macrophages. In current investigation, we studied the role of JNK MAPK signal transduction pathway in rF1-induced activation of macrophages in vitro. SP600125, a specific inhibitor of JNK, inhibited JNK MAPK phosphorylation, indicating the specificity of the above response. Though, the rF1-induced phosphorylation of JNK MAPK was also inhibited by upstream protein kinase C inhibitor H7, tyrosine kinase inhibitor genestein and PI3-K inhibitor wotmannin. Activation of the transcription factor NF-kB (phosphorylation of IkB) and c-Jun was observed in response to rF1 treatment. The rF1-induced JNK MAPK activity was correlated to the functional activation of macrophages by demonstrating the inhibition of NO, TNF-alpha production and microtubule polymerization caused by SP600125. Taken together, the data suggests the involvement of JNK MAPK/NF-kB pathway in rF1-induced activation of macrophages.

Recombinant fraction 1 protein of Yersinia pestis activates murine peritoneal macrophages in vitro

Fraction 1 antigen of Yersinia pestis is a capsule protein of 17.5kDa, known to induce thymocyte proliferation and have anti-phagocytic role in macrophages. It serves as a major protective antigen against challenge of Y. pestis by inducing high concentration of IgG1 antibody response. In the present investigation it is observed that 10microg/ml of rF1 antigen activated murine peritoneal macrophages in vitro. rF1 induced the production of TNF-alpha, IL-1, IL-6, and NO. rF1 treatment also induced increased transcription of IFN-gamma and its related chemokines KC, IP-10, MIP-1alpha, MIP-1beta, MCP-1, RANTES in macrophages. Significantly increased transcription of TLR5 was observed in macrophages treated with rF1, while the expression of TLR2 and TLR4 remained unaffected.

Yersinia V antigen induces both TLR homo- and heterotolerance in an IL-10-involving manner

The virulence antigen (LcrV) of pathogenic yersiniae "silences" macrophages against stimulation with the TLR2-agonist zymosan A in a CD14/TLR2-dependent fashion via IL-10 induction. This pathogenically important "silencing" resembles TLR tolerance phenomena; in these, pre-exposure to a primary tolerizing TLR-agonist renders macrophages unresponsive to stimulation with a secondary challenging TLR-agonist which may involve either the same (TLR homotolerance) or a different TLR (TLR heterotolerance) as the primary TLR-agonist. Here, we show that rLcrV induces TLR homo- and heterotolerance against TLR2- or TLR4-agonists both in human and murine macrophages, respectively. The underlying mechanism of LcrV-induced tolerance is most likely not due to changes in TLR2- or TLR4 expression, but involves LcrV-mediated IL-10 production, since LcrV-induced TLR homo- and heterotolerance is highly impaired in IL-10(-/-) macrophages. Moreover, the involvement of IL-10 in TLR tolerance induction seems to be a more general phenomenon as shown by experiments using different TLR-agonists in IL-10(-/-) macrophages. Since LcrV acts as a secreted protein upon macrophages without requiring direct cell contact, as shown in transwell assays, we propose that yersiniae exploit IL-10-involving TLR tolerance mechanisms by the virulence factor LcrV.