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IL-16 promotes T. whipplei replication by inhibiting phagosome conversion and modulating macrophage activation.

Ghigo E, Barry AO, Pretat L, Al Moussawi K, Desnues B, Capo C, Kornfeld H, Mege JL - PLoS ONE (2010)

Bottom Line: Second, the full transcriptional response of murine macrophages to T. whipplei showed that T. whipplei specifically modulated the expression of 231 probes in IL-16(-/-) macrophages.Gene Ontology analysis revealed that 10 of 13 over-represented terms were linked to immune responses, including proinflammatory transcriptional factors of the NF-κB family.Our results demonstrated a previously unreported function for IL-16 in promoting bacterial replication through inhibited phagolysosome biogenesis and modulated macrophage activation program.

View Article: PubMed Central - PubMed

Affiliation: URMITE, CNRS UMR 6236-IRD 3R198, Université de la Méditerranée, Marseille, France.

ABSTRACT
The replication of Tropheryma whipplei (the agent of Whipple's disease) within human macrophages is associated with the expression of IL-16, a cytokine known for its chemotactic and inflammatory properties. In this study, we asked whether IL-16 acts on T. whipplei replication by interfering with the endocytic pathway. We observed that in macrophages, T. whipplei was located within late phagosomes that were unable to fuse with lysosomes; in monocytes, T. whipplei was eliminated in phagolysosomes. Moreover, adding IL-16 to monocytes induced bacterial replication and inhibited phagolysosome formation. On the other hand, blocking IL-16 activity, either with anti-IL-16 antibodies in human macrophages or by using murine IL-16(-/-) bone marrow-derived macrophages, inhibited T. whipplei replication and rescued phagolysosome biogenesis. Furthermore, we propose that IL-16-mediated interference with the endocytic pathway is likely related to macrophage activation. First, IFNγ induced T. whipplei elimination and phagolysosome formation and inhibited IL-16 production by macrophages. Second, the full transcriptional response of murine macrophages to T. whipplei showed that T. whipplei specifically modulated the expression of 231 probes in IL-16(-/-) macrophages. Gene Ontology analysis revealed that 10 of 13 over-represented terms were linked to immune responses, including proinflammatory transcriptional factors of the NF-κB family. Our results demonstrated a previously unreported function for IL-16 in promoting bacterial replication through inhibited phagolysosome biogenesis and modulated macrophage activation program.

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Analysis of transcriptional responses of BMDMs to T. whipplei.BMDMs were stimulated with T. whipplei (50 bacteria/cell) for six hours and host responses were analyzed using whole genome microarrays. (A) Significant features were compared between wt (blue) and IL-16−/− (green) BMDMs and represented by a Venn diagram. Common significant features are displayed in grey. (B) Significantly over-represented GO biological processes in T. whipplei-stimulated wt (blue) and IL-16−/− (green) BMDM were determined by applying the two-tailed Fisher's exact test (p<0.05).
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pone-0013561-g008: Analysis of transcriptional responses of BMDMs to T. whipplei.BMDMs were stimulated with T. whipplei (50 bacteria/cell) for six hours and host responses were analyzed using whole genome microarrays. (A) Significant features were compared between wt (blue) and IL-16−/− (green) BMDMs and represented by a Venn diagram. Common significant features are displayed in grey. (B) Significantly over-represented GO biological processes in T. whipplei-stimulated wt (blue) and IL-16−/− (green) BMDM were determined by applying the two-tailed Fisher's exact test (p<0.05).

Mentions: As wt BMDMs infected with T. whipplei have been shown to display an atypical activation program combining M2 polarization, a type I IFN response and apoptosis [36], host responses towards T. whipplei in IL-16−/− BMDM were monitored using a full genome microarray, and data were compared to those previously reported [36] (GEO database at NCBI, accession number GSE16180). After a six-hour stimulation with T. whipplei, 356 and 273 probes were significantly modulated in wt and IL-16−/− BMDMs, respectively. Among them, only 42 probes were similarly modulated in both wt and IL-16−/− BMDMs (Figure 8A and Table S1). Next, the genes were annotated according to functional classes. Gene Ontology (GO) biological processes at level 3 did not detect major differences between wt and IL-16−/− BMDM responses to T. whipplei (Figure 8B). Indeed, the GO terms of immune response (GO: 0006955), defense response (GO: 0006952), response to external stimulus (GO: 0009605), regulation of biological process (GO: 0050789) and cytokine production (GO: 0001816) were significantly over-represented in both wt and IL-16−/− BMDMs. In contrast, when GO biological processes were analyzed at lower levels, functional differences were identified. For example, analysis of GO biological processes at level 5 revealed 2 over-represented GO terms in wt BMDMs, different from the 13 over-represented GO terms in IL-16−/− BMDMs. Importantly, among these 13 GO terms, 10 were linked to immune response (Figure 8B). A closer analysis of GO biological processes at level 8 revealed that the regulation of the I-κB kinase/NF-κB cascade (GO: 0043122) was over-represented in IL-16−/− BMDMs but not in their wt counterparts (Figure 8B). These observations were further confirmed by an analysis of over-represented genes according to their transcription factors. Specifically, c-Rel and STAT were over-represented in wt BMDMs (Figure 9A), in accordance with recent data demonstrating that T. whipplei induces type I IFN-dependent responses in these cells [36]. In contrast, in IL-16−/− BMDMs, the main transcription factors regulated by T. whipplei were NF-κB, CP2/LBP-1C/LSF and c-Rel (Figure 9B), all involved in inflammatory responses. Taken together, these results show that the activation programs induced by T. whipplei in wt and IL-16−/− BMDMs are different, and that IL-16 might be involved in macrophage activation. This effect was specific because no significant terms were found between wt and IL-16−/− BMDMs stimulated with lipolysaccharide (LPS). Using the FatiGO Compare tool, 11,235 and 12,107 features were significantly modulated in wt and IL-16−/− BMDMs, respectively. The large majority (9121) of them were common to both wt and IL-16−/− BMDMs (Figure S2).


IL-16 promotes T. whipplei replication by inhibiting phagosome conversion and modulating macrophage activation.

Ghigo E, Barry AO, Pretat L, Al Moussawi K, Desnues B, Capo C, Kornfeld H, Mege JL - PLoS ONE (2010)

Analysis of transcriptional responses of BMDMs to T. whipplei.BMDMs were stimulated with T. whipplei (50 bacteria/cell) for six hours and host responses were analyzed using whole genome microarrays. (A) Significant features were compared between wt (blue) and IL-16−/− (green) BMDMs and represented by a Venn diagram. Common significant features are displayed in grey. (B) Significantly over-represented GO biological processes in T. whipplei-stimulated wt (blue) and IL-16−/− (green) BMDM were determined by applying the two-tailed Fisher's exact test (p<0.05).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2958842&req=5

pone-0013561-g008: Analysis of transcriptional responses of BMDMs to T. whipplei.BMDMs were stimulated with T. whipplei (50 bacteria/cell) for six hours and host responses were analyzed using whole genome microarrays. (A) Significant features were compared between wt (blue) and IL-16−/− (green) BMDMs and represented by a Venn diagram. Common significant features are displayed in grey. (B) Significantly over-represented GO biological processes in T. whipplei-stimulated wt (blue) and IL-16−/− (green) BMDM were determined by applying the two-tailed Fisher's exact test (p<0.05).
Mentions: As wt BMDMs infected with T. whipplei have been shown to display an atypical activation program combining M2 polarization, a type I IFN response and apoptosis [36], host responses towards T. whipplei in IL-16−/− BMDM were monitored using a full genome microarray, and data were compared to those previously reported [36] (GEO database at NCBI, accession number GSE16180). After a six-hour stimulation with T. whipplei, 356 and 273 probes were significantly modulated in wt and IL-16−/− BMDMs, respectively. Among them, only 42 probes were similarly modulated in both wt and IL-16−/− BMDMs (Figure 8A and Table S1). Next, the genes were annotated according to functional classes. Gene Ontology (GO) biological processes at level 3 did not detect major differences between wt and IL-16−/− BMDM responses to T. whipplei (Figure 8B). Indeed, the GO terms of immune response (GO: 0006955), defense response (GO: 0006952), response to external stimulus (GO: 0009605), regulation of biological process (GO: 0050789) and cytokine production (GO: 0001816) were significantly over-represented in both wt and IL-16−/− BMDMs. In contrast, when GO biological processes were analyzed at lower levels, functional differences were identified. For example, analysis of GO biological processes at level 5 revealed 2 over-represented GO terms in wt BMDMs, different from the 13 over-represented GO terms in IL-16−/− BMDMs. Importantly, among these 13 GO terms, 10 were linked to immune response (Figure 8B). A closer analysis of GO biological processes at level 8 revealed that the regulation of the I-κB kinase/NF-κB cascade (GO: 0043122) was over-represented in IL-16−/− BMDMs but not in their wt counterparts (Figure 8B). These observations were further confirmed by an analysis of over-represented genes according to their transcription factors. Specifically, c-Rel and STAT were over-represented in wt BMDMs (Figure 9A), in accordance with recent data demonstrating that T. whipplei induces type I IFN-dependent responses in these cells [36]. In contrast, in IL-16−/− BMDMs, the main transcription factors regulated by T. whipplei were NF-κB, CP2/LBP-1C/LSF and c-Rel (Figure 9B), all involved in inflammatory responses. Taken together, these results show that the activation programs induced by T. whipplei in wt and IL-16−/− BMDMs are different, and that IL-16 might be involved in macrophage activation. This effect was specific because no significant terms were found between wt and IL-16−/− BMDMs stimulated with lipolysaccharide (LPS). Using the FatiGO Compare tool, 11,235 and 12,107 features were significantly modulated in wt and IL-16−/− BMDMs, respectively. The large majority (9121) of them were common to both wt and IL-16−/− BMDMs (Figure S2).

Bottom Line: Second, the full transcriptional response of murine macrophages to T. whipplei showed that T. whipplei specifically modulated the expression of 231 probes in IL-16(-/-) macrophages.Gene Ontology analysis revealed that 10 of 13 over-represented terms were linked to immune responses, including proinflammatory transcriptional factors of the NF-κB family.Our results demonstrated a previously unreported function for IL-16 in promoting bacterial replication through inhibited phagolysosome biogenesis and modulated macrophage activation program.

View Article: PubMed Central - PubMed

Affiliation: URMITE, CNRS UMR 6236-IRD 3R198, Université de la Méditerranée, Marseille, France.

ABSTRACT
The replication of Tropheryma whipplei (the agent of Whipple's disease) within human macrophages is associated with the expression of IL-16, a cytokine known for its chemotactic and inflammatory properties. In this study, we asked whether IL-16 acts on T. whipplei replication by interfering with the endocytic pathway. We observed that in macrophages, T. whipplei was located within late phagosomes that were unable to fuse with lysosomes; in monocytes, T. whipplei was eliminated in phagolysosomes. Moreover, adding IL-16 to monocytes induced bacterial replication and inhibited phagolysosome formation. On the other hand, blocking IL-16 activity, either with anti-IL-16 antibodies in human macrophages or by using murine IL-16(-/-) bone marrow-derived macrophages, inhibited T. whipplei replication and rescued phagolysosome biogenesis. Furthermore, we propose that IL-16-mediated interference with the endocytic pathway is likely related to macrophage activation. First, IFNγ induced T. whipplei elimination and phagolysosome formation and inhibited IL-16 production by macrophages. Second, the full transcriptional response of murine macrophages to T. whipplei showed that T. whipplei specifically modulated the expression of 231 probes in IL-16(-/-) macrophages. Gene Ontology analysis revealed that 10 of 13 over-represented terms were linked to immune responses, including proinflammatory transcriptional factors of the NF-κB family. Our results demonstrated a previously unreported function for IL-16 in promoting bacterial replication through inhibited phagolysosome biogenesis and modulated macrophage activation program.

Show MeSH
Related in: MedlinePlus