Impaired immune functions of monocytes and macrophages in Whipple's disease

Widespread colonization of the lung by Tropheryma whipplei in HIV infection

RATIONALE

Lung infections caused by opportunistic or virulent pathogens are a principal cause of morbidity and mortality in HIV infection. It is unknown whether HIV infection leads to changes in basal lung microflora, which may contribute to chronic pulmonary complications that increasingly are being recognized in individuals infected with HIV.

OBJECTIVES

To determine whether the immunodeficiency associated with HIV infection resulted in alteration of the lung microbiota.

METHODS

We used 16S ribosomal RNA targeted pyrosequencing and shotgun metagenomic sequencing to analyze bacterial gene sequences in bronchoalveolar lavage (BAL) and mouths of 82 HIV-positive and 77 HIV-negative subjects.

MEASUREMENTS AND MAIN RESULTS

Sequences representing Tropheryma whipplei, the etiologic agent of Whipple's disease, were significantly more frequent in BAL of HIV-positive compared with HIV-negative individuals. T. whipplei dominated the community (>50% of sequence reads) in 11 HIV-positive subjects, but only 1 HIV-negative individual (13.4 versus 1.3%; P = 0.0018). In 30 HIV-positive individuals sampled longitudinally, antiretroviral therapy resulted in a significantly reduced relative abundance of T. whipplei in the lung. Shotgun metagenomic sequencing was performed on eight BAL samples dominated by T. whipplei 16S ribosomal RNA. Whole genome assembly of pooled reads showed that uncultured lung-derived T. whipplei had similar gene content to two isolates obtained from subjects with Whipple's disease.

CONCLUSIONS

Asymptomatic subjects with HIV infection have unexpected colonization of the lung by T. whipplei, which is reduced by effective antiretroviral therapy and merits further study for a potential pathogenic role in chronic pulmonary complications of HIV infection.

Evaluation of arginine metabolism for the analysis of M1/M2 macrophage activation in human clinical specimens

BACKGROUND

Macrophage heterogeneity reflects their plasticity in response to environmental stimuli. Usually human macrophages are characterized by analysis of surface molecules or cytokine expression while functional assays are established in the mouse system but lacking for various human specimens.

METHODS

To evaluate the value of analysis of arginine metabolism for characterization of human macrophage differentiation, we analyzed nitrite production and arginase activity in plasma, duodenal biopsies, and in vitro differentiated macrophages of patients with classical Whipple's disease.

RESULTS

We demonstrate that it is feasible to determine the content of urea in supernatants of stimulated duodenal biopsies, arginase activity in fresh duodenal biopsies and plasma samples, and arginase activity and nitrite production in lysates and supernatants of in vitro differentiated macrophages. However, only selected tests are appropriate to define macrophage polarization in human specimens.

CONCLUSION

Analysis of arginine metabolism is not suitable for the characterization of in vitro differentiated human macrophages. Besides the measurement of nitrite in duodenal biopsy supernatants, the determination of arginase activity in human plasma seems to be a reasonable functional test to detect enhanced M2 macrophage activation and, thus, is of great value for the analysis of macrophage activity with a minimum of material and costs.

Tropheryma whipplei as a commensal bacterium

Tropheryma whipplei is the bacterial agent of the well-known and rare Whipple's disease, mainly observed among Caucasians. This bacterium has recently been involved in other chronic and acute infections. For a long time, the only known source of the bacterium was patients with Whipple's disease; however, thanks to the advent of molecular biology, T. whipplei has now been detected in specimens from healthy individuals, mainly in stool and saliva samples. The prevalence of carriage depends on several factors, such as age, exposure and geographical area, reaching 75% in stool specimens from children less than 4 years old in rural Africa. T. whipplei is a commensal bacterium that only causes Whipple's disease in a subset of individuals, probably those with a still-uncharacterized specific immunological defect.

Resolution of whipple disease-induced pulmonary hypertension following antibiotic therapy

Whipple disease is a disorder caused by Tropheryma whipplei, a ubiquitous Gram-positive bacillus. In addition to gastrointestinal manifestations, many other systems may be involved in Whipple disease. Pulmonary hypertension (PH) is a rare manifestation of Whipple disease, and its clinical course is not well established. We report a case of a 45-year-old woman who presented with typical gastrointestinal manifestations of Whipple disease, which was diagnosed by duodenal biopsy. She was also noted to have elevated pulmonary arterial pressures on transthoracic echocardiography. There was no evidence of left-sided valvular disease, hypertrophy, or dyskinesis, and there was no evidence of endocarditis. The patient was started on intravenous ceftriaxone for 6 weeks and then transitioned to oral trimethoprim-sulfamethoxazole for a year. The patient demonstrated clinical improvement, endoscopic and histologic improvement, and also resolution of PH. This is the third reported case of PH that is convincingly secondary to Whipple disease that resolved after appropriate antibiotic therapy.

Whipple's disease

Whipple's disease is a chronic multisystemic infection, due to Tropheryma whipplei, a bacterium ubiquitously present in the environment. Although it is very rare, its clinical features are non-specific and can affect several different districts. Whipple's disease is therefore a condition that should always be kept in mind by doctors working in several branches of medicine, such as internal medicine, gastroenterology, rheumatology, neurology, and cardiology. The condition is fatal if not promptly recognized and treated, but the best treatment is still not completely defined, especially in relapsing disease, neurological manifestations, and in cases of immunoreconstitution after initiation of antibiotic treatment.

Infectious causes of chronic diarrhoea

Infections are an uncommon cause of chronic diarrhoea. Parasites are most likely, including protozoa like giardia, cryptosporidia and cyclospora. Bacteria are unlikely to cause chronic diarrhoea in immunocompetent individuals with the possible exception of Yersinia, Plesiomonas and Aeromonas. Infectious diarrhoea can trigger other causes of chronic diarrhoea, including inflammatory bowel disease, irritable bowel syndrome and "Brainerd-type" diarrhoea. A thorough evaluation should detect most infections causing chronic diarrhoea.

Haemophilus ducreyi-induced interleukin-10 promotes a mixed M1 and M2 activation program in human macrophages

During microbial infection, macrophages are polarized to classically activated (M1) or alternatively activated (M2) cells in response to microbial components and host immune mediators. Proper polarization of macrophages is critical for bacterial clearance. To study the role of macrophage polarization during Haemophilus ducreyi infection, we analyzed a panel of macrophage surface markers in skin biopsy specimens of pustules obtained from experimentally infected volunteers. Lesional macrophages expressed markers characteristic of both M1 and M2 polarization. Monocyte-derived macrophages (MDM) also expressed a mixed M1 and M2 profile of surface markers and cytokines/chemokines upon infection with H. ducreyi in vitro. Endogenous interleukin 10 (IL-10) produced by infected MDM downregulated and enhanced expression of several M1 and M2 markers, respectively. Bacterial uptake, mediated mainly by class A scavenger receptors, and activation of mitogen-activated protein kinase and phosphoinositide 3-kinase signaling pathways were required for H. ducreyi-induced IL-10 production in MDM. Compared to M1 cells, IL-10-polarized M2 cells displayed enhanced phagocytic activity against H. ducreyi and similar bacterial killing. Thus, IL-10-modulated macrophage polarization may contribute to H. ducreyi clearance during human infection.

Comparative analysis of the interaction of Helicobacter pylori with human dendritic cells, macrophages, and monocytes

Helicobacter pylori may cause chronic gastritis, gastric cancer, or lymphoma. Myeloid antigen-presenting cells (APCs) are most likely involved in the induction and expression of the underlying inflammatory responses. To study the interaction of human APC subsets with H. pylori, we infected monocytes, monocyte-derived dendritic cells (DCs), and monocyte-derived (classically activated; M1) macrophages with H. pylori and analyzed phenotypic alterations, cytokine secretion, phagocytosis, and immunostimulation. Since we detected CD163(+) (alternatively activated; M2) macrophages in gastric biopsy specimens from H. pylori-positive patients, we also included monocyte-derived M2 macrophages in the study. Upon H. pylori infection, monocytes secreted interleukin-1β (IL-1β), IL-6, IL-10, and IL-12p40 (partially secreted as IL-23) but not IL-12p70. Infected DCs became activated, as shown by the enhanced expression of CD25, CD80, CD83, PDL-1, and CCR7, and secreted IL-1β, IL-6, IL-10, IL-12p40, IL-12p70, and IL-23. However, infection led to significantly downregulated CD209 and suppressed the constitutive secretion of macrophage migration inhibitory factor (MIF). H. pylori-infected M1 macrophages upregulated CD14 and CD32, downregulated CD11b and HLA-DR, and secreted mainly IL-1β, IL-6, IL-10, IL-12p40, and IL-23. Activation of DCs and M1 macrophages correlated with increased capacity to induce T-cell proliferation and decreased phagocytosis of dextran. M2 macrophages upregulated CD14 and CD206 and secreted IL-10 but produced less of the proinflammatory cytokines than M1 macrophages. Thus, H. pylori affects the functions of human APC subsets differently, which may influence the course and the outcome of H. pylori infection. The suppression of MIF in DCs constitutes a novel immune evasion mechanism exploited by H. pylori.

Regulatory T cells in patients with Whipple's disease

Classical Whipple's disease (CWD) is caused by chronic infection with Tropheryma whipplei that seems to be associated with an underlying immune defect. The pathognomonic hallmark of CWD is a massive infiltration of the duodenal mucosa with T. whipplei-infected macrophages that disperse systemically to many other organ systems. An alleviated inflammatory reaction and the absence of T. whipplei-specific Th1 reactivity support persistence and systemic spread of the pathogen. In this article, we hypothesized that regulatory T cells (T(reg)) are involved in immunomodulation in CWD, and we asked for the distribution, activation, and regulatory capacity of T(reg) in CWD patients. Whereas in the lamina propria of CWD patients before treatment numbers of T(reg) were increased, percentages in the peripheral blood were similar in CWD patients and healthy controls. However, peripheral T(reg) of CWD patients were more activated than those of controls. Elevated secretion of IL-10 and TGF-β in the duodenal mucosa of CWD patients indicated locally enhanced T(reg) activity. Enhanced CD95 expression on peripheral memory CD4(+) T cells combined with reduced expression of IFN-γ and IL-17A upon polyclonal stimulation by CD4(+) cells from untreated CWD patients further hinted to T(reg) activity-related exhaustion of effector CD4(+) T cells. In conclusion, increased numbers of T(reg) can be detected within the duodenal mucosa in untreated CWD, where huge numbers of T. whipplei-infected macrophages are present. Thus, T(reg) might contribute to the chronic infection and systemic spread of T. whipplei in CWD but in contrast prevent mucosal barrier defect by reducing local inflammation.

Macrophage polarization and bacterial infections

PURPOSE OF REVIEW

Macrophages are the first line of defense against pathogens, and the mode of their activation will determine the success or failure of the host response to pathogen aggression. Based on limited numbers of markers, activated macrophages can be classified as classically activated (M1) macrophages that support microbicidal activity or alternatively activated (M2) macrophages that are not competent to eliminate pathogens. The development of high-throughput gene expression methods affords a reappraisal of the concept of macrophage activation in human infectious diseases.

RECENT FINDINGS

By combining microarray data and conventional approaches, it is becoming clear that the M1 polarization program is associated with gastrointestinal infections (e.g. typhoid fever and Helicobacter pylori gastritis) and active tuberculosis. An M2 signature is observed in lepromatous leprosy, Whipple's disease, and localized infections (keratitis, chronic rhinosinusitis). However, these findings could not be predicted from the analysis of the M1/M2 programs of macrophages stimulated in vitro.

SUMMARY

The reappraisal of macrophage polarization by high-throughput methods is critical to understanding the role of macrophage polarization in infectious diseases. Only the identification of individual profiles will support promising therapeutic approaches based on target determination.

Orientia tsutsugamushi stimulates an original gene expression program in monocytes: relationship with gene expression in patients with scrub typhus

Orientia tsutsugamushi is the causal agent of scrub typhus, a public health problem in the Asia-Pacific region and a life-threatening disease. O. tsutsugamushi is an obligate intracellular bacterium that mainly infects endothelial cells. We demonstrated here that O. tsutsugamushi also replicated in monocytes isolated from healthy donors. In addition, O. tsutsugamushi altered the expression of more than 4,500 genes, as demonstrated by microarray analysis. The expression of type I interferon, interferon-stimulated genes and genes associated with the M1 polarization of macrophages was significantly upregulated. O. tsutsugamushi also induced the expression of apoptosis-related genes and promoted cell death in a small percentage of monocytes. Live organisms were indispensable to the type I interferon response and apoptosis and enhanced the expression of M1-associated cytokines. These data were related to the transcriptional changes detected in mononuclear cells isolated from patients with scrub typhus. Here, the microarray analyses revealed the upregulation of 613 genes, which included interferon-related genes, and some features of M1 polarization were observed in these patients, similar to what was observed in O. tsutsugamushi-stimulated monocytes in vitro. This is the first report demonstrating that monocytes are clearly polarized in vitro and ex vivo following exposure to O. tsutsugamushi. These results would improve our understanding of the pathogenesis of scrub typhus, during which interferon-mediated activation of monocytes and their subsequent polarization into an M1 phenotype appear critical. This study may give us a clue of new tools for the diagnosis of patients with scrub typhus.

Circulating and tumor-infiltrating myeloid cells predict survival in human pleural mesothelioma

BACKGROUND

Malignant pleural mesothelioma (MPM) tumor cells produce copious amounts of myeloid cell-stimulating factors. The current study examined the prognostic significance of circulating monocytes and tumor-infiltrating macrophages on overall survival in patients with MPM.

METHODS

The authors retrospectively reviewed 667 patients with MPM who underwent cytoreductive surgery at the Brigham and Women's Hospital in Boston, Massachusetts between 1989 and 2009. Kaplan-Meier and Cox proportional hazards models were used to determine the impact of preoperative circulating monocytes on overall survival. Immunohistochemical staining for CD68 was performed on a tissue microarray of MPM tumors from 52 patients undergoing cytoreductive surgery. The phenotype of circulating monocytes and tumor-infiltrating macrophages in 7 additional patients was determined by flow cytometry.

RESULTS

The median survival for all patients was 13.4 months, and 35% of patients had tumors of nonepithelial histology. For patients with nonepithelial compared with epithelial tumors, survival was significantly worse (9.3 months vs 16.6 months; P < .0001), the number of monocytes was significantly higher (580 ± 20 cells/μL vs 520 ± 10 cells/μL; P = .002), and higher monocyte counts were associated with higher tumor stage. Increasing monocyte counts were correlated with poor survival for all patients with MPM. Within MPM tumors, macrophages comprised 27% ± 9% of the tumor area and demonstrated an immunosuppressive phenotype with high expression of CD163, CD206, and interleukin-4 receptor α. The degree of macrophage infiltration was found to be negatively correlated with survival in patients with nonepithelial (P = .008) but not those with epithelial (P = .7) MPM, independent of disease stage.

CONCLUSIONS

Higher numbers of circulating monocytes are associated with poor survival in all patients with MPM and higher densities of tumor-infiltrating macrophages are associated with poor survival in patients with nonepithelial MPM. Both may enable a novel target for immunotherapy.

Intestinal macrophages and response to microbial encroachment

Macrophages in the gastrointestinal mucosa represent the largest pool of tissue macrophages in the body. In order to maintain mucosal homeostasis, resident intestinal macrophages uniquely do not express the lipopolysaccharide (LPS) co-receptor CD14 or the IgA (CD89) and IgG (CD16, 32, and 64) receptors, yet prominently display Toll-like receptors (TLRs) 3-9. Remarkably, intestinal macrophages also do not produce proinflammatory cytokines in response to TLR ligands, likely because of extracellular matrix (stromal) transforming growth factor-β (TGF-β) dysregulation of nuclear factor (NF)-κB signal proteins and, via Smad signaling, expression of IκBα, thereby inhibiting NF-κB-mediated activities. Thus, in noninflamed mucosa, resident macrophages are inflammation anergic but retain avid scavenger and host defense function, an ideal profile for macrophages in close proximity to gut microbiota. In the event of impaired epithelial integrity during intestinal infection or inflammation, however, blood monocytes also accumulate in the lamina propria and actively pursue invading microorganisms through uptake and degradation of the organism and release of inflammatory mediators. Consequently, resident intestinal macrophages are inflammation adverse, but when the need arises, they receive assistance from newly recruited circulating monocytes.

Specific and nonspecific B-cell function in the small intestines of patients with Whipple's disease

Whipple's disease is a chronic multisystemic infection caused by Tropheryma whipplei that is characterized by arthritis, weight loss, and diarrhea. The immunological defects in the duodenal mucosa, the site of major replication of the agent underlying the pathogenesis of Whipple's disease, are poorly understood. Mucosal immunoglobulins are essential for the defense against intestinal pathogens; therefore, we analyzed the B-cell response in duodenal specimens and sera of Whipple's disease patients. Whereas systemic immunoglobulin production was affected only marginally, duodenal biopsy specimens of Whipple's disease patients contained reduced numbers of immunoglobulin-positive plasma cells and secreted less immunoglobulin compared to healthy controls but showed a weak secretory IgA response toward T. whipplei. This T. whipplei-specific intestinal immune response was not observed in controls. Thus, we were able to demonstrate that general mucosal immunoglobulin production in Whipple's disease patients is impaired. However, this deficiency does not completely abolish T. whipplei-specific secretory IgA production that nonetheless does not protect from chronic infection.