HIV/SIV enteropathy

Transmissible Gastroenteritis Virus Infection Promotes the Self-Renewal of Porcine Intestinal Stem Cells via Wnt/β-Catenin Pathway

Intestinal stem cells (ISCs) play an important role in tissue repair after injury. A recent report delineates the effect of transmissible gastroenteritis virus (TGEV) infection on the small intestine of recovered pigs. However, the mechanism behind the epithelium regeneration upon TGEV infection remains unclear. To address this, we established a TGEV infection model based on the porcine intestinal organoid monolayer. The results illustrated that the porcine intestinal organoid monolayer was susceptible to TGEV. In addition, the TGEV infection initiated the interferon and inflammatory responses following the loss of absorptive enterocytes and goblet cells. However, TGEV infection did not disturb epithelial integrity but induced the proliferation of ISCs. Furthermore, TGEV infection activated the Wnt/β-catenin pathway by upregulating the accumulation and nuclear translocation of β-catenin, as well as promoting the expression of Wnt target genes, such as C-myc, Cyclin D1, Mmp7, Lgr5, and Sox9, which were associated with the self-renewal of ISCs. Collectively, these data demonstrated that the TGEV infection activated the Wnt/β-catenin pathway to promote the self-renewal of ISCs and resulted in intestinal epithelium regeneration. IMPORTANCE The intestinal epithelium is a physical barrier to enteric viruses and commensal bacteria. It plays an essential role in maintaining the balance between the host and intestinal microenvironment. In addition, intestinal stem cells (ISCs) are responsible for tissue repair after injury. Therefore, prompt self-renewal of intestinal epithelium will facilitate the rebuilding of the physical barrier and maintain gut health. In the manuscript, we found that the transmissible gastroenteritis virus (TGEV) infection did not disturb epithelial integrity but induced the proliferation of ISCs and facilitated epithelium regeneration. Detailed mechanism investigations revealed that the TGEV infection activated the Wnt/β-catenin pathway to promote the self-renewal of ISCs and resulted in intestinal epithelium regeneration. These findings will contribute to understanding the mechanism of intestinal epithelial regeneration and reparation upon viral infection.

Gut Microbiome Alterations in Men Who Have Sex with Men-a Preliminary Report

BACKGROUND

Studies have found that HIV is mainly transmitted through the mucosal surface, and the entrance of early progression of the disease is the rectal and colonic mucosa. So, this paper aimed to explore and analyze the structural differences of gut microbiome between men who have sex with men (MSM) and those who haven't sex with men (Non-MSM), expecting finding novel biological factors that potentially impact transmission and/or disease in MSM population.

METHODS

We collected a total of 33 stool samples, 16 were MSM and 17 were Non-MSM. The 16S rRNA gene amplification sequencing was used to detect the alteration and structure of the gut microbiome community in two groups.

RESULTS

The difference in β diversity of gut microbiome of two groups of subjects was statistically significant (P<0.001), indicating that the difference in the structure of the gut microbiome of two groups was statistically significant. Compared with the phylum and genus level of Non-MSM group, the relative abundances of Actinobacteria, Proteobacteria, genera Collinsella, Prevotella, Bifidobacterium and Ralstonia in MSM group were higher (P<0.001, P<0.05, LDA score(log10)>2), and the relative abundance of Bacteroidetes, genera Erysipelotrichaceae incertae sedis, Bilophila, Holdemania, Clostridium XIVb and Bacteroidaceae in MSM group was lower (P<0.01, LDA score(log10)>2).

CONCLUSIONS

There are some differences in the structure of gut microbiome between MSM group and Non-MSM group. It indicates the differences in behavior and characteristics between MSM and Non-MSM population may be related to the difference in the structure of gut microbiome.

Asymptomatic small intestinal ulcerative lesions: Obesity and Helicobacter pylori are likely to be risk factors

It is often difficult to explain why ulcerative lesions are found in the small intestine because there are no obvious aggressors such as gastric acid. In particular, the treatment of small intestinal ulcerative lesions in asymptomatic patients with no symptoms, normal physical examinations, and normal blood test findings is not well documented. According to a summary of capsule endoscopy studies in healthy subjects, approximately 10% of subjects have small intestinal mucosal breaks. The number of mucosal breaks in these instances is approximately 1-3. We examined small intestinal mucosal breaks in healthy subjects recruited from our past two studies. Mucosal breaks were observed in approximately 10% of subjects, and the average number was 0.24 ± 1.21. The number of mucosal breaks in the small intestine was correlated with body mass index and was significantly higher in Helicobacter pylori-infected subjects and higher in males. These results indicate that 1-2 small ulcerative lesions, such as erosions in the small intestine, can be considered to be in the normal range, and close examination is not required. It is assumed that a follow-up medical examination is required for such asymptomatic persons. The presence of many small ulcerative lesions or an unequivocal ulcer indicates an abnormality for which close examination is desired. However, in many cases, it is sufficient to scrutinize after detecting anemia, but it is difficult to make a judgment due to insufficient reports, and future studies are required.

Gastrointestinal manifestations of human immunodeficiency virus and coronavirus disease 2019: Understanding the intersecting regions between the two epidemics

In March 2020, the World Health Organization declared coronavirus disease (COVID-19) a pandemic. As of February 2021, there were 107 million COVID-19 cases worldwide. As a comparison, there are approximately 38 million people living with human immunodeficiency virus (PLHIV) worldwide. The coexistence of both epidemics, and the syndemic effect of both viruses could lead to a delirious impact both at individual and community levels. Many intersecting points were found between severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the causative agent of COVID-19, and HIV; among which, gastrointestinal (GI) manifestations are the most notable.

GI manifestations represent a common clinical presentation in both HIV and SARS-CoV-2. The emergence of GI symptoms as a result of SARS-CoV-2 infection provides a new dynamic to COVID-19 diagnosis, management, and infection control measures, and adds an additional diagnostic challenge in case of coinfection with HIV. The presence of GI manifestations in PLHIV during the COVID-19 pandemic could be referred to HIV enteropathy, presence of opportunistic infection, adverse effect of antiretrovirals, or coinfection with COVID-19. Thus, it is important to exclude SARS-CoV-2 in patients who present with new-onset GI manifestations, especially in PLHIV, to avoid the risk of disease transmission during endoscopic interventions.

Structural similarities between both viruses adds a valuable intersecting point, which has mutual benefits in the management of both viruses. These similarities led to the hypothesis that antiretrovirals such as lopinavir/Rironavir have a role in the management of COVID-19, which was the target of our search strategy using the available evidence. These similarities may also facilitate the development of an efficient HIV vaccine in the future using the advances in COVID-19 vaccine development.

Integrin α4β7 in HIV-1 infection: A critical review

Over the past decade, a series of observations linking α4β7, the principal gut-homing integrin, with various aspects of HIV-1 infection have generated considerable interest in the field of HIV-1 research. After the initial report that the major HIV-1 envelope glycoprotein, gp120, can bind to α4β7, intensive research efforts have been focused on the role of α4β7 as a key factor in HIV-1 pathogenesis and as a potential target for prevention and treatment. The interaction between α4β7 and its natural ligand, MAdCAM-1, directs infected CD4⁺ T cells and HIV-1 virions carrying incorporated α4β7 to the gut mucosa, which may facilitate HIV-1 seeding and replication in the intestinal compartment during the early stages of infection. In addition, cells that express high levels of α4β7, such as Th17 cells, represent preferential targets for infection, and their frequency in the circulation was shown to correlate with susceptibility to HIV-1 infection and disease progression. A number of in vivo studies in nonhuman primates have investigated whether blockage of α4β7 may affect SIV transmission and pathogenesis. Administration of a primatized anti-α4β7 antibody that blocks MAdCAM-1 binding to α4β7 was reported to reduce SIV mucosal transmission in rhesus macaques. However, the mechanism responsible for such a protective effect is still undefined, and conflicting results have been reported on the effects of the same antibody, in combination with ART, during the early chronic phase of SIV infection. Thus, despite a series of tantalizing results accrued over the past decade, the jury is still out on the role of α4β7 in HIV-1 infection.

HIV, Sexual Orientation, and Gut Microbiome Interactions

Recent studies have raised interest in the possibility that dysbiosis of the gut microbiome (i.e., the communities of bacteria residing in the intestine) in HIV-infected patients could contribute to chronic immune activation, and, thus, to elevated mortality and increased risk of inflammation-related clinical diseases (e.g., stroke, cardiovascular disease, cancer, long-bone fractures, and renal dysfunction) found even in those on effective antiretroviral therapy. Yet, to date, a consistent pattern of HIV-associated dysbiosis has not been identified. What is becoming clear, however, is that status as a man who has sex with men (MSM) may profoundly impact the structure of the gut microbiota, and that this factor likely confounded many HIV-related intestinal microbiome studies. However, what factor associated with MSM status drives these gut microbiota-related changes is unclear, and what impact, if any, these changes may have on the health of MSM is unknown. In this review, we outline available data on changes in the structure of the gut microbiome in HIV, based on studies that controlled for MSM status. We then examine what is known regarding the gut microbiota in MSM, and consider possible implications for research and the health of this population. Lastly, we discuss knowledge gaps and needed future studies.

Infectious Threats, the Intestinal Barrier, and Its Trojan Horse: Dysbiosis

The ecosystem of the gut microbiota consists of diverse intestinal species with multiple metabolic and immunologic activities and it is closely connected with the intestinal epithelia and mucosal immune response, with which it builds a complex barrier against intestinal pathogenic bacteria. The microbiota ensures the integrity of the gut barrier through multiple mechanisms, either by releasing antibacterial molecules (bacteriocins) and anti-inflammatory short-chain fatty acids or by activating essential cell receptors for the immune response. Experimental studies have confirmed the role of the intestinal microbiota in the epigenetic modulation of the gut barrier through posttranslational histone modifications and regulatory mechanisms induced by epithelial miRNA in the epithelial lumen. Any quantitative or functional changes of the intestinal microbiota, referred to as dysbiosis, alter the immune response, decrease epithelial permeability and destabilize intestinal homeostasis. Consequently, the overgrowth of pathobionts (Staphylococcus, Pseudomonas, and Escherichia coli) favors intestinal translocations with Gram negative bacteria or their endotoxins and could trigger sepsis, septic shock, secondary peritonitis, or various intestinal infections. Intestinal infections also induce epithelial lesions and perpetuate the risk of bacterial translocation and dysbiosis through epithelial ischemia and pro-inflammatory cytokines. Furthermore, the decline of protective anaerobic bacteria (Bifidobacterium and Lactobacillus) and inadequate release of immune modulators (such as butyrate) affects the release of antimicrobial peptides, de-represses microbial virulence factors and alters the innate immune response. As a result, intestinal germs modulate liver pathology and represent a common etiology of infections in HIV immunosuppressed patients. Antibiotic and antiretroviral treatments also promote intestinal dysbiosis, followed by the selection of resistant germs which could later become a source of infections. The current article addresses the strong correlations between the intestinal barrier and the microbiota and discusses the role of dysbiosis in destabilizing the intestinal barrier and promoting infectious diseases.

Disruption of Intestinal Homeostasis and Intestinal Microbiota During Experimental Autoimmune Uveitis

Purpose

We determine the changes in intestinal microbiota and/or disruptions in intestinal homeostasis during uveitis.

Methods

Experimental autoimmune uveitis (EAU) was induced in B10.RIII mice with coadministration of interphotoreceptor retinoid-binding protein peptide (IRBP) and killed mycobacterial antigen (MTB) as an adjuvant. Using 16S rRNA gene sequencing, we looked at intestinal microbial differences during the course of uveitis, as well as intestinal morphologic changes, changes in intestinal permeability by FITC-dextran leakage, antimicrobial peptide expression in the gastrointstinal tract, and T lymphocyte prevalence before and at peak intraocular inflammation.

Results

We demonstrate that increased intestinal permeability and antimicrobial peptide expression in the intestinal tract coincide in timing with increased effector T cells in the mesenteric lymph nodes, during the early stages of uveitis, before peak inflammation. Morphologic changes in the intestine were most prominent during this phase, but also occurred with adjuvant MTB alone, whereas increased intestinal permeability was found only in IRBP-immunized mice that develop uveitis. We also demonstrate that the intestinal microbiota were altered during the course of uveitis, and that some of these changes are specific to uveitic animals, whereas others are influenced by adjuvant MTB alone. Intestinal permeability peaked at 2 weeks, coincident with an increase in intestinal bacterial strain differences, peak lipocalin production, and peak uveitis.

Conclusions

An intestinal dysbiosis accompanies a disruption in intestinal homeostasis in autoimmune uveitis, although adjuvant MTB alone promotes intestinal disruption as well. This may indicate a novel axis for future therapeutic targeting experimentally or clinically.

Not All That Flattens Villi Is Celiac Disease: A Review of Enteropathies

Enteropathies can be overwhelming for clinicians. There is a wide spectrum of diseases involved; their effect on patients can be severe; and their underlying cause can be obscure. In this article, we outline a practical approach to enteropathies that are most common and not to be missed and is applicable to general and specialist physicians.

Marked Enteropathy in an Accelerated Macaque Model of AIDS

Enteropathy in HIV infection is not eliminated with combination antiretroviral therapy and is possibly linked to microbial translocation. We used a rapidly progressing SIV/pigtailed macaque model of HIV to examine enteropathy and microbial translocation. Histologic evidence of intestinal disease was observed in only half of infected macaques during late-stage infection (LSI). Combination antiretroviral therapy initiated during acute infection prevented intestinal disease. In the ileum and colon, enteropathy was associated with increased caspase-3 staining, decreased CD3⁺ T cells, and increased SIV-infected cells. CD3⁺ T cells were preserved in LSI animals without intestinal disease, and levels of CD3 staining in all LSI animals strongly correlated with the number of infected cells in the intestine and plasma viral load. Unexpectedly, there was little evidence of microbial translocation as measured by soluble CD14, soluble CD163, lipopolysaccharide binding protein, and microbial 16s ribosomal DNA. Loss of epithelial integrity indicated by loss of the tight junction protein claudin-3 was not observed during acute infection despite significantly fewer T cells. Claudin-3 was reduced in LSI animals with severe intestinal disease but did not correlate with increased microbial translocation. LSI animals that did not develop intestinal disease had increased T-cell intracytoplasmic antigen 1-positive cytotoxic T lymphocytes, suggesting a robust adaptive cytotoxic T-lymphocyte response may, in part, confer resilience to SIV-induced intestinal damage.

Gastrointestinal viral load and enteroendocrine cell number are associated with altered survival in HIV-1 infected individuals

Human immunodeficiency virus type 1 (HIV-1) infects and destroys cells of the immune system leading to an overt immune deficiency known as HIV acquired immunodeficiency syndrome (HIV/AIDS). The gut associated lymphoid tissue is one of the major lymphoid tissues targeted by HIV-1, and is considered a reservoir for HIV-1 replication and of major importance in CD4+ T-cell depletion. In addition to immunodeficiency, HIV-1 infection also directly causes gastrointestinal (GI) dysfunction, also known as HIV enteropathy. This enteropathy can manifest itself as many pathological changes in the GI tract. The objective of this study was to determine the association of gut HIV-1 infection markers with long-term survival in a cohort of men who have sex with men (MSM) enrolled pre-HAART (Highly Active Antiretroviral Therapy). We examined survival over 15-years in a cohort of 42 HIV-infected cases: In addition to CD4+ T cell counts and HIV-1 plasma viral load, multiple gut compartment (duodenum and colon) biopsies were taken by endoscopy every 6 months during the initial 3-year period. HIV-1 was cultured from tissues and phenotyped and viral loads in the gut tissues were determined. Moreover, the tissues were subjected to an extensive assessment of enteroendocrine cell distribution and pathology. The collected data was used for survival analyses, which showed that patients with higher gut tissue viral load levels had a significantly worse survival prognosis. Moreover, lower numbers of serotonin (duodenum) and somatostatin (duodenum and colon) immunoreactive cell counts in the gut tissues of patients was associated with significant lower survival prognosis. Our study, suggested that HIV-1 pathogenesis and survival prognosis is associated with altered enteroendocrine cell numbers, which could point to a potential role for enteroendocrine function in HIV infection and pathogenesis.

HIV infection and the intestinal mucosal barrier

HIV infection induces a barrier defect of the intestinal mucosa, which is closely linked to immune activation and CD4 T cell depletion. The HIV-induced barrier defect is initiated in early acute and maintained through chronic infection. In acute infection, increased epithelial permeability is associated with increased epithelial apoptosis possibly caused by perforin-expressing cytotoxic T cells. In chronic infection, mucosal production of inflammatory cytokines is associated with increased epithelial permeability, epithelial apoptosis, and alterations of epithelial tight junctions. In addition to HIV-induced immune-mediated effects, viral proteins have the potential to directly affect epithelial barrier function. After prolonged viral suppression by antiretroviral therapy, there is, at least partial, restoration of the HIV-associated intestinal mucosal barrier defect despite persisting alterations of the mucosal immune system.

Microbial translocation in HIV infection: causes, consequences and treatment opportunities

Systemic immune activation is increased in HIV-infected individuals, even in the setting of virus suppression with antiretroviral therapy. Although numerous factors may contribute, microbial products have recently emerged as potential drivers of this immune activation. In this Review, we describe the intestinal damage that occurs in HIV infection, the evidence for translocation of microbial products into the systemic circulation and the pathways by which these products activate the immune system. We also discuss novel therapies that disrupt the translocation of microbial products and the downstream effects of microbial translocation.

Plasmacytoid dendritic cells are recruited to the colorectum and contribute to immune activation during pathogenic SIV infection in rhesus macaques

In SIV/HIV infection, the gastrointestinal tissue dominates as an important site because of the impact of massive mucosal CD4 depletion and immune activation-induced tissue pathology. Unlike AIDS-susceptible rhesus macaques, natural hosts do not progress to AIDS and resolve immune activation earlier. Here, we examine the role of dendritic cells (DCs) in mediating immune activation and disease progression. We demonstrate that plasmacytoid DCs (pDCs) in the blood up-regulate β7-integrin and are rapidly recruited to the colorectum after a pathogenic SIV infection in rhesus macaques. These pDCs were capable of producing proinflammatory cytokines and primed a T cytotoxic 1 response in vitro. Consistent with the up-regulation of β7-integrin on pDCs, in vivo blockade of α4β7-integrin dampened pDC recruitment to the colorectum and resulted in reduced immune activation. The up-regulation of β7-integrin expression on pDCs in the blood also was observed in HIV-infected humans but not in chronically SIV-infected sooty mangabeys that show low levels of immune activation. Our results uncover a new mechanism by which pDCs influence immune activation in colorectal tissue after pathogenic immunodeficiency virus infections.

Correlation between CD4+ T-cell loss and Gag-specific T cells in different intestinal sites of chronically SIV-infected rhesus monkeys

OBJECTIVE

To determine the loss of CD4+ T cells and virus-specific cytotoxic T cells (CTL) in different mucosal sites of rhesus monkeys infected with simian immunodeficiency virus (SIV).

DESIGN

A cross-sectional comparative investigation of seven different mucosal sites from chronically SIV-infected rhesus monkeys was performed by analyzing blood and mucosal lymphocytes.

METHODS

Mucosal lymphocytes were isolated from duodenum, jejunum, ileum and colon as well as from vagina, cervix and uterus of SIV-infected rhesus monkeys at necropsy. CD4+ T cells and SIV-Gag-specific CTL were determined in blood and mucosal samples by flow cytometry.

RESULTS

A significant depletion of CD4+ T cells was observed in blood and all mucosal sites of SIV-infected rhesus monkeys compared to uninfected animals. But the mean percentage loss of CD4+ T cells varied between 66 and 95% between the different mucosal tissues. The frequency of CTL ranged between 0.4 and 2.4% with the highest proportions in vagina and cervix. Among the intestinal sites the mean levels of CTL correlated with mean percentage loss of CD4+ T cells.

CONCLUSION

A discriminative pronounced loss of CD4+ T cells among the mucosal tissues confirmed that viral replication affects different mucosal sites in a distinct way. Despite high levels of CTL, especially in vagina and cervix, the severe loss of mucosal CD4+ T cells could not be prevented during chronic SIV infection. However, within the four sites of the intestine a high virus-specific cellular immune response correlated with better preservation of CD4+ T cells.

Th17 cytokines and the gut mucosal barrier

Local immune responses serve to contain infections by pathogens to the gut while preventing pathogen dissemination to systemic sites. Several subsets of T cells in the gut (T-helper 17 cells, gammadelta T cells, natural killer (NK), and NK-T cells) contribute to the mucosal response to pathogens by secreting a subset of cytokines including interleukin (IL)-17A, IL-17F, IL-22, and IL-26. These cytokines induce the secretion of chemokines and antimicrobial proteins, thereby orchestrating the mucosal barrier against gastrointestinal pathogens. While the mucosal barrier prevents bacterial dissemination from the gut, it also promotes colonization by pathogens that are resistant to some of the inducible antimicrobial responses. In this review, we describe the contribution of Th17 cytokines to the gut mucosal barrier during bacterial infections.

Advances in sexually transmitted infections of the gastrointestinal tract

The gastrointestinal mucosa is a target of many sexually transmitted infections, and major advances have increased our understanding of the consequences of such infections within the gastrointestinal system. HIV-1 is associated with a marked loss of mucosal CD4(+) T cells that express CC-chemokine receptor 5. This process seems to be more rapid and more severe in mucosa-associated lymphoid tissue than in the peripheral blood. Mechanistic insights into the underlying cause of acute and chronic gastrointestinal damage with HIV infection-microbial translocation, defects in intestinal epithelial barrier function and activation of a systemic immune response-have also been achieved. Increased understanding of the pathogenesis of mucosal HIV-1 infection may identify therapeutic targets to restore immunological function and the integrity of the intestinal mucosal epithelial barrier. The increasing prevalence of lymphogranuloma venereum in Europe, mostly in HIV-positive men who have sex with men, suggests a change in the epidemiology of what was previously considered to be a 'tropical' disease. The increasing incidence of acute HCV infection transmitted via sexual contact has also been fueled by high-risk sexual behaviors among men who have sex with men, many of whom are also HIV-positive. The first part of this Review discusses the pathogenesis and gastrointestinal complications of HIV infection, and the second part summarizes advances in our understanding of other sexually transmitted infections of the gastrointestinal system.

Immunopathogenesis of asymptomatic chronic HIV Infection: the calm before the storm

PURPOSE OF REVIEW

HIV and pathogenic simian immunodeficiency virus infection are characterized by chronic immune activation. This review addresses the factors that influence immune activation and may thus determine the rate of disease progression during the asymptomatic period of HIV.

RECENT FINDINGS

Immune activation stems from foreign antigen stimulation, including HIV, microbial products and coinfections and compensatory homeostatic mechanisms. Continuous immune stimulation creates a permissive environment for further viral replication, while temporarily allowing successful replenishment of the T-cell pool. Type I interferon, microbial translocation, activated (but ineffective) effector T cells, unruly regulatory T cells and inadequate T helper 17 cells all play important roles in the cycle of activation, functional exhaustion and T-cell death that leads to immunodeficiency.

SUMMARY

The asymptomatic chronic phase of HIV infection is a dynamic balance between host and virus, the outcome of which determines an individual's course of disease. Evaluation of the factors that determine the immunologic threshold of disease progression could assist in designing therapeutic strategies, including individualized timing of ART.

The role of secondary lymphatic tissue in immune deficiency of HIV infection

HIV infection is a disease primarily of lymphatic tissues, in which most viral replication occurs in CD4 T cells. The most common measures of the impact of HIV infection are made by counting CD4 T cells in peripheral blood. Peripheral blood, however, contains only 2% of the total CD4 cell population in the body and these are typically effector memory cells in transit; the vast majority of CD4 cells reside in the secondary lymphoid tissues (e.g. lymph nodes and mucosal lymphatic tissues) and the impact of HIV replication is most profound on the population residing within these compartments. Within organized follicular aggregates in mucosal tissues and the very precise structures of lymph nodes most viral replication occurs in the parafollicular T-cell zone, both in primary infection and throughout the course of the disease, such that by the time the patient presents with symptoms of HIV seroconversion approximately 50% of the population is already depleted. Therefore, if we are to understand the pathophysiology and pathogenesis of HIV and its related complications fully, we need to examine the structure and function of secondary lymphoid tissues before and during HIV infection and before and during HIV treatment. This may provide valuable insights into the underlying pathogenesis of a range of disorders associated with HIV infection, and potentially aid in the development of therapies aimed at emerging complications of long-term HIV infection.

Simian immunodeficiency virus-induced intestinal cell apoptosis is the underlying mechanism of the regenerative enteropathy of early infection

The enteropathic manifestations of the human immunodeficiency virus (HIV) and the simian immunodeficiency virus (SIV) in late infection are usually due to infection by other microbes, but in early infection the viruses themselves cause an enteropathy by heretofore undetermined mechanisms. Here we report that SIV induces massive apoptosis of intestinal epithelial cells lining the small and large bowel, thus identifying apoptosis as the driving force behind the regenerative pathology of early infection. We found that apoptosis of gut epithelium paralleled the previously documented apoptosis and massive depletion of CD4 T cells in gut lamina propria, triggered by established mechanisms of gut epithelial cell apoptosis and, at peak, possibly by virus interactions with GPR15/Bob, an intestinal epithelial cell-associated alternative coreceptor for SIV and HIV-1. Apoptosis in early SIV infection is thus the common theme of the pathological processes that quickly afflict the innate as well as adaptive arms of the gut immune system.

FIV infection induces unique changes in phenotype and cellularity in the medial iliac lymph node and intestinal IEL

Studies of human immunodeficiency virus-1 (HIV-1)-infected patients and simian immunodeficiency virus (SIV)-infected macaques have identified profound depletion of CD4(+) T cells and expansion of CD8(+) T cells in the gastrointestinal lamina propria. Less attention has been given to CD8(+) intraepithelial lymphocytes (IEL), and no studies have concurrently examined inductive sites such as draining lymph nodes. Our preliminary data in the feline immunodeficiency virus (FIV) animal model suggested additional changes in IEL, and marked differences in the responses of lymph nodes draining different mucosal sites. To address this, we quantified the absolute leukocyte yield and examined the phenotype of cells from small intestinal IEL, mesenteric lymph node (MLN), and medial iliac lymph node (ILN) from chronically FIV-infected cats. The cellularity of the ILN was increased 530% in FIV-infected animals with an expansion of CD62L(+) cells, suggesting an increased population of naive T cells. The number of CD4(+), as well as CD8(+), T cells was increased in the ILN, resulting in a CD4:CD8 ratio greater than 1:1. In contrast, reduced cellularity, specific loss of CD4(+) T cells, and inversion of the CD4:CD8 ratio was observed in the MLN, which drains the intestine. In IEL, loss of CD8alpha, CD8beta, and CD4-expressing T cells was found in FIV-infected cats. Furthermore, expression intensity of CD8alpha and CD5, markers known to be important in T cell function, was markedly decreased on IEL. These findings expand the array of immune alterations induced by lentiviral infection and indicate that characterization of multiple mucosal sites will be necessary to fully understand the pathogenesis of HIV-1 infection.

Unique pathology in simian immunodeficiency virus-infected rapid progressor macaques is consistent with a pathogenesis distinct from that of classical AIDS

Simian immunodeficiency virus (SIV) infection of macaques and human immunodeficiency virus type 1 (HIV-1) infection of humans result in variable but generally fatal disease outcomes. Most SIV-infected macaques progress to AIDS over a period of 1 to 3 years, in the face of robust SIV-specific immune responses (conventional progressors [CP]). A small number of SIV-inoculated macaques mount transient immune responses and progress rapidly to AIDS (rapid progressors [RP]). We speculated that the underlying pathogenic mechanisms may differ between RP and CP macaques. We compared the pathological lesions, virus loads, and distribution of virus and target cells in SIVsmE660- or SIVsmE543-infected RP and CP rhesus macaques at terminal disease. RP macaques developed a wasting syndrome characterized by severe SIV enteropathy in the absence of opportunistic infections. In contrast, opportunistic infections were commonly observed in CP macaques. RP and CP macaques showed distinct patterns of CD4(+) T-cell depletion, with a selective loss of memory cells in RP macaques and a generalized (naive and memory) CD4 depletion in CP macaques. In situ hybridization demonstrated higher levels of virus expression in lymphoid tissues (P < 0.001) of RP macaques and a broader distribution to include many nonlymphoid tissues. Finally, SIV was preferentially expressed in macrophages in RP macaques whereas the primary target cells in CP macaques were T lymphocytes at end stage disease. These data suggest distinct pathogenic mechanisms leading to the deaths of these two groups of animals, with CP macaques being more representative of HIV-induced AIDS in humans.

The pathology of malabsorption: current concepts

Intestinal malabsorption results from a wide variety of causes, which can most easily be organized into three groups. Maldigestion arises from problems with mixing or with digestive mediators, and includes post-gastrectomy patients and those with deficiencies of pancreatic or intestinal enzymes, or of bile salts. Mucosal and mural causes of malabsorption are abundant, and include gluten-sensitive enteropathy, tropical sprue, autoimmune enteropathy, and HIV/AIDS-related enteropathy, as well as mural conditions such as systemic sclerosis. Finally, microbial causes of malabsorption include bacterial overgrowth, Whipple's disease, and numerous infections or infestations that are most frequently seen in immunocompromised patients. An overview of the most common and interesting entities in each of these categories follows, along with a discussion of current concepts. Mucosal conditions and microbial causes of malabsorption are given special attention.

HIV enteropathy: crypt stem and transit cell hyperproliferation induces villous atrophy in HIV/Microsporidia-infected jejunal mucosa

OBJECTIVES

The study aim was to analyse the kinetics of stem and transit cells in the crypts of jejunal mucosa infected with HIV and Microsporidia.

DESIGN

The size of villi, depth of crypts and proliferative activity of transit and stem cells in jejunal mucosa were measured using morphometric techniques.

METHODS

The surface area/volume ratio (S/V) of jejunal biopsies was estimated under light microscopy using a Weibel graticule. Crypt length was measured by counting enterocytes along the crypt side from the base to the villus junction, and the mean crypt length was calculated. The S/V and crypt lengths of the jejunal mucosa of 21 HIV and Microsporidia-infected test cases were compared with 14 control cases. The labelling index in relation to the crypt cell position of 10 of the test cases was analysed compared with 13 control cases.

RESULTS

Differences were found in the S/V and crypt length, and there was a negative correlation between S/V and crypt length in test and control cases combined. Cell labelling indices fell into low and high proliferation groups. There were significant differences in labelling indices between low proliferation test cases and controls, between high proliferation test cases and controls, and between high and low proliferation test cases.

CONCLUSION

Villous atrophy induced by HIV and Microsporidia is attributed to crypt cell hyperplasia and the encroachment of crypt cells onto villi. These infections induce crypt hypertrophy by stimulating cell mitosis predominantly in transit cells but also in stem cells. Increased stem cell proliferation occurs only in high proliferation cases.

An approach to duodenal biopsies

The introduction of endoscopy of the upper digestive tract as a routine diagnostic procedure has increased the number of duodenal biopsy specimens. Consequently, the pathologist is often asked to evaluate them. In this review, a practical approach to the evaluation of a duodenal biopsy specimen is discussed. An overview of the handling of specimens is given and the normal histology and commonly encountered diseases are discussed. Finally, a description of commonly seen infections is provided, together with an algorithmic approach for diagnosis.

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Optimization of methods to assess human mucosal T-cell responses to HIV infection

The majority of HIV-1 infections occur via sexual transmission at mucosal epithelia lining the vagina, cervix or rectum. Mucosal tissues also serve as viral reservoirs. However, our knowledge of human mucosal T-cell responses is limited. There is a need for reliable, sensitive, and reproducible methods for assessing mucosal immunity. Here we report on the collaborative efforts of two laboratories to optimize methods for processing, culturing, and analyzing mucosal lymphocytes. Rectal biopsy tissue was obtained by flexible sigmoidoscopy, which is rapid, minimally invasive, and well tolerated. Of the four methods compared for isolating mucosal mononuclear cells (MMC), collagenase digestion reproducibly yielded the most lymphocytes (4-7 x 10(6)). Furthermore, 0.5-1 x 10(6) MMC could be polyclonally expanded to yield 17 x 10(6) CD8+ T cells allowing mapping of responses to overlapping peptides spanning the HIV-1 genome using IFN-gamma enzyme-linked immunospot (ELISpot). Expansion also reduced the spontaneous IFN-gamma production normally detected in fresh MMC. Piperacillin-tazobactam and amphotericin B reduced contamination of MMC cultures to 4%. Taken together, these methods will be useful for studies of mucosal immunity to HIV-1 and other pathogens during natural infection and following vaccination.

Intestinal flora and mucosal immune responses

The normal intestinal flora and the mucosal immune system exist in close spatial proximity. A normal structure and function of both very complex systems is required for health and develops in a constant and interactive process. An abnormal host response to the normal intestinal flora leads to chronic intestinal inflammation. Probiotic bacteria may modulate the intestinal flora and the mucosal immune response and are an effective therapy for remission maintenance of ulcerative colitis and pouchitis.

T helper type-2 cells induce ileal villus atrophy, goblet cell metaplasia, and wasting disease in T cell-deficient mice

BACKGROUND & AIMS

T helper (Th) 1 and Th2 cell subsets significantly influence the pathological features of inflammation in the gastrointestinal tract in a distinct manner. It is now established that the transfer of CD4(+)CD45RB(Hi) (RB(Hi)) T cells to either severe combined immunodeficient (SCID) or recombinase activation gene 2-deficient (RAG(-/-)) mice results in a severe granulomatous hypertrophic colitis mediated by Th1 cells. We have modified this approach to address the role of Th2 cells.

METHODS

RB(Hi) T cells from wild-type (Wt) mice or mice genetically predisposed to Th2 responses (interferon-gamma-defective [IFN-gamma(-/-)]) with or without B cells were transferred to T cell receptor (TCR)-beta and delta-chain-defective (TCR(-/-)) or SCID mice.

RESULTS

Transfer of Wt RB(Hi) T cells induced wasting disease with severe colitis in the TCR(-/-) mice. In contrast, IFN-gamma(-/-) RB(Hi) T cells induced severe weight loss and hypoalbuminemia without significant inflammation in the colon. The small intestine of these mice exhibited villus atrophy, a decrease in brush-border enzymes, reduced enterocyte proliferation, and an increased number of goblet cells. The presence of B cells was necessary for these changes, because SCID recipients required cotransfer of B cells, together with IFN-gamma(-/-) RB(Hi) T cells for ileal lesions to develop. Treatment of TCR(-/-) recipients of IFN-gamma(-/-) RB(Hi) T cells with anti-IL-4 mAb abrogated both the wasting disease and the villus atrophy.

CONCLUSIONS

Dysregulated Th2 cells cause atrophic changes and goblet cell transformation in the small intestinal epithelium and wasting disease mediated by excess interleukin-4 and B cells.

Supernatants of HIV-infected immune cells affect the barrier function of human HT-29/B6 intestinal epithelial cells

OBJECTIVES

Characterization of the diarrhoea-inducing effect of altered cytokine production in HIV infection.

METHODS

Monocyte-derived macrophages (MDM) were infected with macrophagetropic (SF162) and lymphocytotropic (IIIB) HIV-1 strains and cocultured with autologous peripheral blood mononuclear cells (PBMC). After 24 h the supernatants were collected and tested for their immunoreactive levels of cytokines by enzyme-linked immunosorbent assay. The effects of the supernatants and the respective recombinant human cytokines on barrier function of HT-29/B6 cells were determined.

RESULTS

Infection of MDM with HIV-1 SF162 or IIIB led to increased production of tumour necrosis factor-alpha (TNFalpha), interleukin-1-beta, interferon-alpha and interferon-gamma after cell-cell contact with PBMC. Supernatants of infected cells decreased transepithelial resistance (R(t)), with higher effects on R(t) in HIV IIIB infection, which was due to higher cytokine concentrations. The effect was not due to cytotoxicity (negative LDH assay) or epithelial monolayer disruption [zonula occludens protein-1 (ZO-1) immunofluorescence staining]. The effect of HIV-1 IIIB coculture supernatants could be mimicked by the respective recombinant human cytokines. TNFalpha is an effector cytokine, because inhibition of TNFalpha by its soluble receptor decreased the effect of the supernatants on transepithelial resistance. Conductance scanning indicated the cytokine-induced barrier defect to be due to both, induction of epithelial apoptoses and tight junction alterations.

CONCLUSIONS

Cell-cell interaction of HIV-infected macrophages with PBMC leads to a release of cytokines sufficient to alter intestinal epithelial barrier function. The main effect was mediated by TNFalpha inducing a leak-flux which may contribute to the diarrhoea by HIV per se (HIV-enteropathy).

Simian immunodeficiency virus (SIV)-specific cytotoxic T lymphocytes in gastrointestinal tissues of chronically SIV-infected rhesus monkeys

Although systemic virus-specific cytotoxic T lymphocyte (CTL) responses are of critical importance in controlling virus replication in individuals infected with human immunodeficiency virus 1 (HIV-1), little is known about this immune response in the gastrointestinal (GI) tract. This study investigated the GI tract CTL response in a nonhuman primate model for HIV-1 infection, simian immunodeficiency virus (SIV)-infected rhesus monkeys. Lymphocytes from duodenal pinch biopsy specimens were obtained from 9 chronically SIVmac-infected rhesus monkeys and GI tract lymphocytes were harvested from the jejunum and ileum of 4 euthanized SIVmac-infected rhesus monkeys. Lymphocytes were also assessed in GI mucosal tissues by in situ staining in histologic specimens. SIVmac Gag-specific CTLs were assessed in the monkeys using the tetramer technology. These GI mucosal tissues of chronically SIVmac-infected rhesus monkeys contained levels of CTLs comparable to those found in the peripheral blood and lymph nodes. The present studies suggest that the CD8(+) CTL response in GI mucosal sites is comparable to that seen systemically in SIVmac-infected rhesus monkeys.