Human galectin-1 and galectin-3 promote Tropheryma whipplei infection.

Tropheryma whipplei, is an actinobacterium that causes different infections in humans, including Whipple's disease. The bacterium infects and replicates in macrophages, leading to a Th2-biased immune response. Previous studies have shown that T. whipplei harbors complex surface glycoproteins with evidence of sialylation. However, the exact contribution of these glycoproteins for infection and survival remains obscure. To address this, we characterized the bacterial glycoprofile and evaluated the involvement of human ß-galactoside-binding lectins, Galectin-1 (Gal-1) and Galectin-3 (Gal-3) which are highly expressed by macrophages as receptors for bacterial glycans. Tropheryma whipplei glycoproteins harbor different sugars including glucose, mannose, fucose, ß-galactose and sialic acid. Mass spectrometry identification revealed that these glycoproteins were membrane- and virulence-associated glycoproteins. Most of these glycoproteins are highly sialylated and N-glycosylated while some of them are rich in poly-N-acetyllactosamine (Poly-LAcNAc) and bind Gal-1 and Gal-3. In vitro, T. whipplei modulates the expression and cellular distribution of Gal-1 and Gal-3. Although both galectins promote T. whipplei infection by enhancing bacterial cell entry, only Gal-3 is required for optimal bacterial uptake. Finally, we found that serum levels of Gal-1 and Gal-3 were altered in patients with T. whipplei infections as compared to healthy individuals, suggesting that galectins are also involved in vivo. Among T. whipplei membrane-associated proteins, poly-LacNAc rich-glycoproteins promote infection through interaction with galectins. T. whipplei modulates the expression of Gal-1 and Gal-3 both in vitro and in vivo. Drugs interfering with galectin-glycan interactions may provide new avenues for the treatment and diagnosis of T. whipplei infections.

Tropheryma whipplei, the agent of Whipple's disease, affects the early to late phagosome transition and survives in a Rab5- and Rab7-positive compartment.

Tropheryma whipplei, the agent of Whipple's disease, inhibits phago-lysosome biogenesis to create a suitable niche for its survival and replication in macrophages. To understand the mechanism by which it subverts phagosome maturation, we used biochemical and cell biological approaches to purify and characterise the intracellular compartment where Tropheryma whipplei resides using mouse bone-marrow-derived macrophages. We showed that in addition to Lamp-1, the Tropheryma whipplei phagosome is positive for Rab5 and Rab7, two GTPases required for the early to late phagosome transition. Unlike other pathogens, inhibition of PI(3)P production was not the mechanism for Rab5 stabilisation at the phagosome. Overexpression of the inactive, GDP-bound form of Rab5 bypassed the pathogen-induced blockade of phago-lysosome biogenesis. This suggests that Tropheryma whipplei blocks the switch from Rab5 to Rab7 by acting on the Rab5 GTPase cycle. A bio-informatic analysis of the Tropheryma whipplei genome revealed a glyceraldehyde-3-phosphate dehydrogenase (GAPDH) homologous with the GAPDH of Listeria monocytogenes, and this may be the bacterial protein responsible for blocking Rab5 activity. To our knowledge, Tropheryma whipplei is the first pathogen described to induce a "chimeric" phagosome stably expressing both Rab5 and Rab7, suggesting a novel and specific mechanism for subverting phagosome maturation.

Type I interferon induction is detrimental during infection with the Whipple's disease bacterium, Tropheryma whipplei.

Macrophages are the first line of defense against pathogens. Upon infection macrophages usually produce high levels of proinflammatory mediators. However, macrophages can undergo an alternate polarization leading to a permissive state. In assessing global macrophage responses to the bacterial agent of Whipple's disease, Tropheryma whipplei, we found that T. whipplei induced M2 macrophage polarization which was compatible with bacterial replication. Surprisingly, this M2 polarization of infected macrophages was associated with apoptosis induction and a functional type I interferon (IFN) response, through IRF3 activation and STAT1 phosphorylation. Using macrophages from mice deficient for the type I IFN receptor, we found that this type I IFN response was required for T. whipplei-induced macrophage apoptosis in a JNK-dependent manner and was associated with the intracellular replication of T. whipplei independently of JNK. This study underscores the role of macrophage polarization in host responses and highlights the detrimental role of type I IFN during T. whipplei infection.

Tropheryma whipplei infection.

Whipple's disease was initially described in 1907. Over the next century, the clinical and pathological features of this disorder have been better appreciated. Most often, weight loss, diarrhea, abdominal and joint pain occur. Occasionally, other sites of involvement have been documented, including isolated neurological disease, changes in the eyes and culture-negative endocarditis. In the past decade, the responsible organism Tropheryma whipplei has been cultivated, its genome sequenced and its antibiotic susceptibility defined. Although rare, it is a systemic infection that may mimic a wide spectrum of clinical disorders and may have a fatal outcome. If recognized, prolonged antibiotic therapy may be a very successful form of treatment.

Tropheryma whipplei glycosylation in the pathophysiologic profile of Whipple's disease.

BACKGROUND: Tropheryma whipplei is a bacterium commonly found in people with Whipple's disease, a rare systemic chronic infection. In the present study, we hypothesized that bacterium glycosylation may impair the immune response. METHODS: Bacterial extracts were analyzed by glycostaining, and reactive proteins, identified by matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) mass spectometry, were purified to generate antibodies that could be used in immunofluorescence studies. The reactivity of serum samples obtained from patients and asymptomatic carriers was tested against native or deglycosylated bacteria, for which the fate in macrophages was also investigated. RESULTS: To our knowledge, we evidenced, for the first time in T. whipplei, a 110-kDa glycoprotein containing sialic acid. This protein, identified as an Wnt1-inducible signaling pathway (WiSP) protein, is associated with periodic acid-Schiff (PAS) staining in infected intramacrophage biofilm. Consistent with the lack of enzymes required for the glycosylation pathway in this bacterium, the glycoproteins disappear during in vitro axenic subcultures, whereas human transcriptome analysis reveals the up-regulation of corresponding genes within infected macrophages. Proteic antigens are not recognized by the serum samples obtained from patients compared with those obtained from nonsick carriers, and T. whipplei that exhibits a low glycosylation profile does not efficiently multiply in macrophages in vitro. CONCLUSIONS: T. whipplei glycosylation is likely to impair antibody-mediated immune recognition in patients. Such an intracellular antigen masking system in bacteria has not previously been described.