Emerging concepts in gastrointestinal aspects of HIV-1 pathogenesis and management

Smad7 as a positive regulator of intestinal inflammatory diseases

In physiological conditions, the human gut contains more immune cells than the rest of the body, but no overt tissue damage occurs, because several regulatory mechanisms control the activity of such cells thus preventing excessive and detrimental responses. One such mechanism relies on the action of transforming growth factor (TGF)-β1, a cytokine that targets both epithelial cells and many immune cell types. Loss of TGF-β1 function leads to intestinal pathology in both mice and humans. For instance, disruption of TGF-β1 signaling characterizes the destructive immune-inflammatory response in patients with Crohn's disease and patients with ulcerative colitis, the major human inflammatory bowel disease (IBD) entities. In these pathologies, the defective TGF-β1-mediated anti-inflammatory response is associated with elevated intestinal levels of Smad7, an antagonist of TGF-β1 signaling. Consistently, knockdown of Smad7 restores TGF-β1 function thereby attenuating intestinal inflammation in patients with IBD as well as in mice with IBD-like colitis. Up-regulation of Smad7 and reduced TGF-β1 signaling occurs also in necrotizing enterocolitis, environmental enteropathy, refractory celiac disease, and cytomegalovirus-induced colitis. In this article, we review the available data supporting the pathogenic role of Smad7 in the gastrointestinal tract and discuss whether and how targeting Smad7 can help attenuate detrimental immuno-inflammatory responses in the gut.

Involvement of Smad7 in Inflammatory Diseases of the Gut and Colon Cancer

In physiological conditions, the human intestinal mucosa is massively infiltrated with various subsets of immune cells, the activity of which is tightly regulated by several counter-regulatory factors. One of these factors is transforming growth factor-β1 (TGF-β1), a cytokine produced by multiple cell types and targeting virtually all the intestinal mucosal cells. Binding of TGF-β1 to its receptors triggers Smad2/3 signaling, thus culminating in the attenuation/suppression of immune–inflammatory responses. In patients with Crohn’s disease and patients with ulcerative colitis, the major human inflammatory bowel diseases (IBD), and in mice with IBD-like colitis, there is defective TGF-β1/Smad signaling due to high levels of the intracellular inhibitor Smad7. Pharmacological inhibition of Smad7 restores TGF-β1 function, thereby reducing inflammatory pathways in patients with IBD and colitic mice. On the other hand, transgenic over-expression of Smad7 in T cells exacerbates colitis in various mouse models of IBD. Smad7 is also over-expressed in other inflammatory disorders of the gut, such as refractory celiac disease, necrotizing enterocolitis and cytomegalovirus-induced colitis, even though evidence is still scarce and mainly descriptive. Furthermore, Smad7 has been involved in colon carcinogenesis through complex and heterogeneous mechanisms, and Smad7 polymorphisms could influence cancer prognosis. In this article, we review the data about the expression and role of Smad7 in intestinal inflammation and cancer.

Cytomegalovirus promotes intestinal macrophage-mediated mucosal inflammation through induction of Smad7

Intestinal macrophages in healthy human mucosa are profoundly down-regulated for inflammatory responses (inflammation anergy) due to stromal TGF-β inactivation of NF-κB. Paradoxically, in cytomegalovirus (CMV) intestinal inflammatory disease, one of the most common manifestations of opportunistic CMV infection, intestinal macrophages mediate severe mucosal inflammation. Here we investigated the mechanism whereby CMV infection promotes macrophage-mediated mucosal inflammation. CMV infected primary intestinal macrophages but did not replicate in the cells or reverse established inflammation anergy. However, CMV infection of precursor blood monocytes, the source of human intestinal macrophages in adults, prevented stromal TGF-β-induced differentiation of monocytes into inflammation anergic macrophages. Mechanistically, CMV up-regulated monocyte expression of the TGF-β antagonist Smad7, blocking the ability of stromal TGF-β to inactivate NF-κB, thereby enabling MyD88 and NF-κB-dependent cytokine production. Smad7 expression also was markedly elevated in mucosal tissue from subjects with CMV colitis and declined after antiviral ganciclovir therapy. Confirming these findings, transfection of Smad7 antisense oligonucleotide into CMV-infected monocytes restored monocyte susceptibility to stromal TGF-β-induced inflammation anergy. Thus, CMV-infected monocytes that recruit to the mucosa, not resident macrophages, are the source of inflammatory macrophages in CMV mucosal disease and implicate Smad7 as a key regulator of, and potential therapeutic target for, CMV mucosal disease.

Innate immunity in HIV-1 infection: epithelial and non-specific host factors of mucosal immunity- a workshop report

The interplay between HIV-1 and epithelial cells represents a critical aspect in mucosal HIV-1 transmission. Epithelial cells lining the oral cavity cover subepithelial tissues, which contain virus-susceptible host cells including CD4(+) T lymphocytes, monocytes/macrophages, and dendritic cells. Oral epithelia are among the sites of first exposure to both cell-free and cell-associated virus HIV-1 through breast-feeding and oral-genital contact. However, oral mucosa is considered to be naturally resistant to HIV-1 transmission. Oral epithelial cells have been shown to play a crucial role in innate host defense. Nevertheless, it is not clear to what degree these local innate immune factors contribute to HIV-1 resistance of the oral mucosa. This review paper addressed the following issues that were discussed at the 7th World Workshop on Oral Health and Disease in AIDS held in Hyderabad, India, during November 6-9, 2014: (i) What is the fate of HIV-1 after interactions with oral epithelial cells?; (ii) What are the keratinocyte and other anti-HIV effector oral factors, and how do they contribute to mucosal protection?; (iii) How can HIV-1 interactions with oral epithelium affect activation and populations of local immune cells?; (iv) How can HIV-1 interactions alter functions of oral epithelial cells?

The Effects of HIV Infection on Oral Mucosal Immunity

Oral mucosal infections, especially candidiasis, are a feature of HIV disease, suggesting that compromised mucosal immunity within the oral cavity is a consequence of the viral infection. However, how this mucosal immunity is compromised and at what stage of HIV infection this occurs are unclear. Better understanding of the protection of the oral cavity against infection has allowed us to gain some insight into the local consequences of HIV infection. From a humoral perpective, IgA2 subclasses are reduced in HIV infection in saliva, and total secretory IgA levels are reduced in later disease. Similarly, mucosal antibody responses appear near normal in early HIV infection but reduced in AIDS. There is now convincing evidence that salivary IgA can be neutralizing to HIV 1 and HIV 2, as well as block epithelial transmigration. Oral cellular immunity is also affected by HIV infection. Transmission of HIV from one oral cell type to another appears to be confirmed by work showing that HIV can bind to or infect epithelial cells, Langerhans cells, and other mucosal cells. CXCR4 tropic ( via GalCer and CXCR4) and dual tropic HIV strains have been shown to be able to infect normal human oral keratinocytes (NHOKs), and infectious HIV virions can also be conveyed from NHOKs to activated peripheral blood lymphocytes, suggesting a potential role of oral epithelial cells in the transmission of HIV infection. There is evidence of up-regulation of various receptors, including HIV receptors, on the surface of oral epithelium, and the epithelium may become more permeable. HIV may exploit this antigen uptake mechanism to cross epithelial barriers during co-infection with damage-inducing pathogens such as Candida. Immune responsiveness to many of the co-pathogens associated with HIV has been demonstrated to depend on a family of innate recognition molecules, known as Toll-like receptors (TLR), and recognition of a single pathogen can involve activation of multiple TLRs. Consequently, TLR-pathogen interactions could play an indirect but major role in regulating HIV-associated disease in the oral cavity. Thus, HIV infection appears to have both direct and indirect effects on oral mucosal immunity, affecting both cellular and humoral immunity as well as both specific and innate immunity.

Adverse Effects Associated With Antiretroviral Therapy and Potential Management Strategies

A variety of adverse drug reactions (ADRs) affecting many organ systems may be observed with antiretroviral therapy (ARV), and they can be differentiated into short- and long- term effects, class effects, or individual drug effects. Commonly seen ADRs include dermatological reactions, associated with nonnucleoside reverse transcriptase inhibitors (NNRTIs) and some protease inhibitors (PIs), and gastrointestinal problems, a major side effect of PIs and of some nucleoside reverse transcriptase inhibitors (NRTIs). Metabolic complications are frequently reported in HIV-infected patients on ARV and often coexist. Lipodystrophy, hyperinsulinemia/hyperglycemia, and bone disorders (osteoporosis, osteonecrosis) are mainly associated with PIs, while lactic acidemia/acidosis are primarily a problem of NRTIs. Hyperlipidemia may be caused by almost all PIs, few NRTIs, and NNRTIs. All antiretroviral drug classes may cause both asymptomatic and symptomatic hepatotoxicity, although nevirapine is the agent most implicated in hepatic events. More drug-specific ADRs include nephrotoxicity (indinavir and tenofovir), central nervous system problems (efavirenz), hematological disturbances (zidovudine), and hypersensitivity reactions (abacavir). Anticipation of ADRs may influence a patient’s decision to delay ARV or to choose specific and potentially less active agents. Occurrence of ADRs may significantly impact a patient’s quality of life and drug adherence. Pharmacists counseling HIV-infected patients should be aware of common ADRs with ARV and potential management strategies.

Oral epithelial cells and their interactions with HIV-1

As the AIDS pandemic has continued, our understanding of the events that occur during the entry and infection of conventional, susceptible cells has increased dramatically, leading to the development of control therapies for HIV-infected individuals. However, an ongoing hole in our understanding is how HIV crosses the mucosal barriers to gain access to permissive cells, despite how important this information would be in developing successful vaccines and other preventative measures such as topical anti-HIV microbicides. In particular, our knowledge of the role that epithelial cells of the mucosal surfaces play in infection - both during early phases and throughout the life of an infected individual, is currently hazy at best. However, several studies in recent years suggest that HIV can bind to and traverse these mucosal epithelial cells, providing a reservoir of infection that can subsequently infect underlying permissive cells. Despite this interaction with epithelial cells, evidence suggests HIV-1 does not productively infect these cells, although they are capable of transferring surface-bound and transcytosed virus to other, permissive cells. Further, there appear to be key differences between adult and infant epithelial cells in the degree to which HIV can transcytose and infect the epithelium. Thus, it is clear that, whilst not primary targets for infection and virus replication, epithelial cells play an important role in the infection cycle and improving our understanding of their interactions with HIV could potentially provide key insights necessary to develop effective preventative therapies.

Oral and vaginal epithelial cell lines bind and transfer cell-free infectious HIV-1 to permissive cells but are not productively infected

The majority of HIV-1 infections worldwide are acquired via mucosal surfaces. However, unlike the vaginal mucosa, the issue of whether the oral mucosa can act as a portal of entry for HIV-1 infection remains controversial. To address potential differences with regard to the fate of HIV-1 after exposure to oral and vaginal epithelium, we utilized two epithelial cell lines representative of buccal (TR146) and pharyngeal (FaDu) sites of the oral cavity and compared them with a cell line derived from vaginal epithelium (A431) in order to determine (i) HIV-1 receptor gene and protein expression, (ii) whether HIV-1 genome integration into epithelial cells occurs, (iii) whether productive viral infection ensues, and (iv) whether infectious virus can be transferred to permissive cells. Using flow cytometry to measure captured virus by HIV-1 gp120 protein detection and western blot to detect HIV-1 p24 gag protein, we demonstrate that buccal, pharyngeal and vaginal epithelial cells capture CXCR4- and CCR5-utilising virus, probably via non-canonical receptors. Both oral and vaginal epithelial cells are able to transfer infectious virus to permissive cells either directly through cell-cell attachment or via transcytosis of HIV-1 across epithelial cells. However, HIV-1 integration, as measured by real-time PCR and presence of early gene mRNA transcripts and de novo protein production were not detected in either epithelial cell type. Importantly, both oral and vaginal epithelial cells were able to support integration and productive infection if HIV-1 entered via the endocytic pathway driven by VSV-G. Our data demonstrate that under normal conditions productive HIV-1 infection of epithelial cells leading to progeny virion production is unlikely, but that epithelial cells can act as mediators of systemic viral dissemination through attachment and transfer of HIV-1 to permissive cells.

Clinical value of duodenal biopsies--beyond the diagnosis of coeliac disease

At upper gastrointestinal endoscopy to investigate unexplained diarrhea and iron deficiency anemia, duodenal biopsies are often taken to exclude a diagnosis of coeliac disease. While histology remains the gold standard for this diagnosis, recent developments in serological testing may overtake this as a first line test and biopsy restricted to confirming the diagnosis. Established coeliac disease on biopsy is straightforward, but early lesions may pose a challenge. Newer endoscopic procedures such as push-pull enteroscopy (balloon enteroscopy) with biopsy allow access to the small bowel beyond the second part of the duodenum. Controversy remains as to what constitutes the normal histology of the duodenum, and small bowel. Lymphocytic duodenosis (increased intraepithelial lymphocytes with normal villous architecture) in patients with negative coeliac serology can be associated with Helicobacter pylori, drugs, autoimmune and other diseases including food allergy. Full thickness small intestinal biopsies can aid in investigation of enteric neuropathies in severe dysmotility disorders. Biopsies are also taken to investigate malabsorption due to suspected infectious and metabolic disorders. Despite highly active anti-retroviral therapy (HAART), immunosuppressed patients may be affected by duodenal pathogens. The histology of duodenal mucosa in acid related disorders reflects the damage seen at endoscopy. Although the prevalence of duodenal ulcer disease is decreasing, drugs causing ulceration remain an important disease entity. Recent observations in functional bowel disorders suggest that the duodenum may be a key site for pathology. In functional dyspepsia, patients with early satiety may have excess eosinophil infiltration, and the mast cell is probably a key player in the irritable syndrome in the small intestine.

Specific prebiotics modulate gut microbiota and immune activation in HAART-naive HIV-infected adults: results of the "COPA" pilot randomized trial

Intestinal mucosal immune system is an early target for human immunodeficiency virus type 1 (HIV-1) infection, resulting in CD4(+) T-cell depletion, deterioration of gut lining, and fecal microbiota composition. We evaluated the effects of a prebiotic oligosaccharide mixture in highly active antiretroviral therapy (HAART)-naive HIV-1-infected adults. In a pilot double-blind, randomized, placebo-controlled study, 57 HAART-naive HIV-1-infected patients received a unique oligosaccharide mixture (15 or 30 g short chain galactooligosaccharides/long chain fructooligosaccharides/pectin hydrolysate-derived acidic oligosaccharides (scGOS/lcFOS/pAOS) daily) or a placebo for 12 weeks. Microbiota composition improved significantly with increased bifidobacteria, decreased Clostridium coccoides/Eubacterium rectale cluster, and decreased pathogenic Clostridium lituseburense/Clostridium histolyticum group levels upon prebiotic supplementation. In addition, a reduction of soluble CD14 (sCD14), activated CD4(+)/CD25(+) T cells, and significantly increased natural killer (NK) cell activity when compared with control group were seen in the treatment group. The results of this pilot trial highly significantly show that dietary supplementation with a prebiotic oligosaccharide mixture results in improvement of the gut microbiota composition, reduction of sCD14, CD4(+) T-cell activation (CD25), and improved NK cell activity in HAART-naive HIV-infected individuals.

Exogenous HIV-1 Nef upsets the IFN-γ-induced impairment of human intestinal epithelial integrity

Background

The mucosal tissues play a central role in the transmission of HIV-1 infection as well as in the pathogenesis of AIDS. Despite several clinical studies reported intestinal dysfunction during HIV infection, the mechanisms underlying HIV-induced impairments of mucosal epithelial barrier are still unclear. It has been postulated that HIV-1 alters enterocytic function and HIV-1 proteins have been detected in several cell types of the intestinal mucosa. In the present study, we analyzed the effect of the accessory HIV-1 Nef protein on human epithelial cell line.

Methodology/Principal Findings

We used unstimulated or IFN-γ-stimulated Caco-2 cells, as a model for homeostatic and inflamed gastrointestinal tracts, respectively. We investigated the effect of exogenous recombinant Nef on monolayer integrity analyzing its uptake, transepithelial electrical resistance, permeability to FITC-dextran and the expression of tight junction proteins. Moreover, we measured the induction of proinflammatory mediators. Exogenous Nef was taken up by Caco-2 cells, increased intestinal epithelial permeability and upset the IFN-γ-induced reduction of transepitelial resistance, interfering with tight junction protein expression. Moreover, Nef inhibited IFN-γ-induced apoptosis and up-regulated TNF-α, IL-6 and MIP-3α production by Caco-2 cells while down-regulated IL-10 production. The simultaneous exposure of Caco-2 cells to Nef and IFN-γ did not affect cytokine secretion respect to untreated cells. Finally, we found that Nef counteracted the IFN-γ induced arachidonic acid cascade.

Conclusion/Significance

Our findings suggest that exogenous Nef, perturbing the IFN-γ-induced impairment of intestinal epithelial cells, could prolong cell survival, thus allowing for accumulation of viral particles. Our results may improve the understanding of AIDS pathogenesis, supporting the discovery of new therapeutic interventions.

Cholera toxin inhibits HIV-1 replication in human colorectal epithelial HT-29 cells through adenylate cyclase activation

Mixed feeding, combining breast milk and nonhuman milk and/or solid food, is a common practice in developing countries that increases the risk of vertical HIV-1 transmission. It also enhances the risk of infection by waterborne microorganisms such as Vibrio cholerae, a diarrhoea-causing pathogen that frequently infects children below 18 months of age. Although both HIV-1 and V. cholerae affect young children and target intestinal epithelial cells, no information is currently available on possible interactions between these two pathogens. In this study, we show for the first time that cholera toxin (CTx), at a concentration as low as 100 pg/ml, inhibits HIV-1 infection of HT-29, a human colorectal epithelial cell line. The CTx-mediated inhibitory effect does not result from a down-regulation of receptor/co-receptor expression or a modulation of viral transcription. Nevertheless, additional experiments indicate that a yet to be identified early step in the virus life cycle is targeted by CTx since the enterotoxin similarly reduces infection of HT-29 cells with AMLV-I, HTLV-I and HIV-1 pseudotyped viruses while exerting no effect on infection with VSV-G pseudotypes. Furthermore, our results indicate that the CTx-dependent suppression is not due to the cholera toxin subunit B but linked instead to the action of cholera toxin subunit A (CTA). Altogether our data indicate that the CTA subunit of CTx is negatively affecting an early event in HIV-1 replication in human colon cancer HT-29 cells.

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.

[Ambulatorial prevalence of hepatitis B and C markers in patients with human immunodeficiency virus infection in a general hospital]

BACKGROUND

Hepatitis B and C viruses and human immunodeficiency virus share the same route of transmission, and the prevalence of HBV and HCV infection in patients infected with HIV is greater than it is in the general population.

AIM

To determine the prevalence of hepatitis B and C markers in a population of patients with HIV as well as the risk factors involved.

PATIENTS AND METHODS

From 5,870 registration forms of patients with HIV of an Infectology Unit, 587 were randomly selected. From these, the 343 which had investigated the presence of any hepatitis B (HBsAg, anti-HBc or anti-HBs) or C (anti-HCV) marker were retrospectively analyzed.

RESULTS

HBsAg was positive in 14/306 (4.6%), anti-HBs was positive in 40/154(26.0%), and anti-HBc in 79/205 (38.5%). The anti-HCV test was reactive in 126/330 (38.2%). HBV and HCV co-infection was observed in 7 of the 296 patients who had both HBsAg and anti-HCV tests (2.4%). For those who were HBsAg positive, the main exposure factor was homosexual intercourse (50.0%). For those who were anti-HCV reactive, the main risk factor was intravenous drug use (75.3%). In the HIV mono-infected (185 patients), the most prevalent exposure risk factor was promiscuous heterosexual practices or sexual intercourse with a spouse infected with HIV (83 patients - 44.9%).

CONCLUSION

In our environment HBV-HIV and HCV-HIV co-infections are frequent, a greater relevance being observed in the association between HCV and HIV.

Zinc fights diarrhoea in HIV-1-infected children: in-vitro evidence to link clinical data and pathophysiological mechanism

Diarrhoea-related morbidity is reduced by zinc supplementation in HIV-1-infected children. The mechanisms of this effect are largely undefined. We provide evidence for role for Tat (transactivating peptide produced by HIV-1) in the pathogenesis of diarrhoea in AIDS patients. In this study we showed that zinc, preventing Tat-induced fluid secretion, directly limits a specific mechanism of HIV-1-related diarrhoea. Our data support a 'zinc approach' in adjunct to specific antiretroviral therapy in HIV-1-infected children.

Mucosal but not peripheral FOXP3+ regulatory T cells are highly increased in untreated HIV infection and normalize after suppressive HAART

Recent evidence indicates that regulatory T cells (T(regs)) play an important role in HIV infection. However, although the gastrointestinal mucosa is a key compartment in HIV disease, no data on mucosal T(regs) in HIV infection are available. In this study, we compared the frequency of T(regs) in duodenal mucosa and peripheral blood (PB) of 13 treatment-naive and 13 suppressively treated HIV-infected patients with that of 6 patients with norovirus infection and 12 healthy controls. T(regs) were quantified by immunohistochemistry (CD3/FOXP3) and further characterized (CD25, CTLA-4, GITR) by immunohistochemistry, immunofluorescence, and fluorescence-activated cell sorting (FACS). Both the frequency and the absolute count of mucosal T(regs) were highly increased in untreated HIV patients but were normal in treated HIV patients. In contrast, in peripheral blood of HIV patients, the absolute number of T(regs) was not increased, and their frequency was only slightly elevated. In norovirus infection, frequency of mucosal T(regs) in the CD4+ T-cell subset was not elevated. The high increase in count and frequency of mucosal T(regs) seems to be a characteristic feature of untreated HIV infection, suggesting a significant contribution of T(regs) to the pathogenesis of HIV disease. Their role may be 2-edged: attenuating HIV-induced immune hyperactivation while suppressing the immune response to HIV and mucosal pathogens.

Mucosal vaccines: the promise and the challenge

Most infectious agents enter the body at mucosal surfaces and therefore mucosal immune responses function as a first line of defence. Protective mucosal immune responses are most effectively induced by mucosal immunization through oral, nasal, rectal or vaginal routes, but the vast majority of vaccines in use today are administered by injection. As discussed in this Review, current research is providing new insights into the function of mucosal tissues and the interplay of innate and adaptive immune responses that results in immune protection at mucosal surfaces. These advances promise to accelerate the development and testing of new mucosal vaccines against many human diseases including HIV/AIDS.

Inhibitory effect of HIV-1 Tat protein on the sodium-D-glucose symporter of human intestinal epithelial cells

OBJECTIVE

The pathophysiology of HIV-1-related intestinal dysfunction is largely unknown. We previously found that the transactivator factor peptide (Tat) produced by HIV-1 induces ion secretion and inhibits cell proliferation in human enterocytes. Because sugar malabsorption is a frequent feature in AIDS patients, we evaluated whether Tat inhibits intestinal glucose absorption.

DESIGN AND METHODS

We measured Na-D-glucose symporter (SGLT-1) activity and determined its phenotypic expression in Caco-2 cells, in the presence and absence of Tat, in uptake experiments using a non-metabolized radiolabelled glucose analogue, and by western blot analysis, respectively. alpha-Tubulin staining was used to study the effects exerted by Tat on cell structure.

RESULTS

Tat dose dependently inhibited glucose uptake by human enterocytes. This effect was prevented by anti-Tat polyclonal antibodies and by L-type Ca channels agonist Bay K8644. Western blot analysis of cellular lysates and brush-border membrane preparations showed that Tat induced SGLT-1 missorting. Tat also caused a dramatic decrease in alpha-tubulin staining, which indicates dysruption of the cytoskeleton organization.

CONCLUSIONS

Tat acutely impairs intestinal glucose absorption through SGLT-1 missorting. This result indicates that Tat is directly involved in AIDS-associated intestinal dysfunction.

Immunopathology of the duodenal mucosa of HIV-positive patients during combined antiretroviral therapy

The objective of the present study was to evaluate the duodenal mucosa of HIV-infected patients during antiretroviral therapy. This was an observational study conducted on HIV-positive patients and a control group. Group 1 comprised 22 HIV-negative individuals while 38 HIV-positive individuals were classified according to the CDC 1993 classification into group 2 (A1 or A2) or group 3 (B2, A3, B3, C2, C3). All subjects were submitted to upper gastrointestinal endoscopy with duodenal biopsies. Qualitative, semi-quantitative and quantitative histological analyses were performed. Results were considered significant when P < 0.05. A higher prevalence of inflammatory infiltrate and eosinophilia was observed in the HIV group, together with a reduction in mucosal CD4+ lymphocyte (L) counts [median (lower-upper quartiles), 12.82 (8.30-20.33), 6.36 (1.75-11.66) and 1.75 (0.87-3.14) in groups 1, 2 and 3, respectively] which was not correlated with disease stage. The extent of CD4+L count reduction was similar in blood and duodenal mucosa. Normal CD8+L and CD45RO+L counts, and normal numbers of macrophages and antigen-presenting cells were also found in the HIV patients. The cytokine pattern did not differ among groups. Tissue HIV, assessed by p24 antigen, correlated with a higher CD45RO+L count (77.0 (61-79.8) and 43.6 (31.7-62.8) in p24+ and p24-, respectively, P = 0.003), and IL-4 positivity (100 and 48.2% in p24+ and p24-, respectively, P = 0.005). The duodenal mucosa of HIV+ patients showed a relatively preserved histological architecture. This finding may be characteristic of a population without opportunistic infections and treated with potent antiretroviral therapy, with a better preservation of the immune status.

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Occurrence of gastrointestinal opportunistic disorders in AIDS despite the use of highly active antiretroviral therapy

Since the introduction of highly active antiretroviral therapy (HAART), the frequency of opportunistic disorders (ODs) of the gastrointestinal (GI) tract in human immunodeficiency virus (HIV)-infected patients has fallen dramatically. We have found, however, that despite the use of HAART, HIV-infected patients can still present with GI ODs. To evaluate the prevalence of GI ODs in HIV-infected patients on HAART who were undergoing endoscopic evaluation for GI-related symptoms. From January 1996 through February 2002, all HIV-infected patients undergoing GI endoscopy were prospectively identified; mucosal biopsies were obtained in a standardized fashion and histologic specimens were examined by a single GI pathologist. All the patients on HAART presenting with a GI OD are described. Results showed that 294 patients (88% men; mean age, 36.5 +/- 10 years; median CD4 lymphocyte count, 64 cells/microl; range, 1-884; median viral RNA level, 40,357 copies/ml; range, 0-7,721,715) underwent 401 upper and/or lower endoscopies during the study period. The use of HAART increased from 10% in early 1996 to 85% in 2002. Nevertheless we found that 27 patients (9%) presented with a GI OD despite HAART. Forty percent of the patients with a GI OD were noncompliant with HAART. We conclude that GI ODs can occur despite HAART and normal CD4 counts. The prevalence of GI ODs in HIV-infected patients taking HAART is 9%. The reasons for this are multifactorial and likely include noncompliance with medications, viral resistance to the drugs, and decreased drug bioavailability. Although the use of HAART has led to a decreased incidence of GI ODs in AIDS, the gastroenterologist evaluating these patients should not discard the possibility that the GI symptoms in HIV-infected patients taking HAART may be secondary to an OD, even when the CD4 count is normal and the viral load is low.

Association of levels of HIV-1-infected breast milk cells and risk of mother-to-child transmission

Understanding how the level of human immunodeficiency virus type 1 (HIV-1)-infected breast milk cells (BMCs) affects HIV transmission via breast-feeding can shed light on the mechanism of infection and aid in establishing effective interventions. The proportion of infected cells to total cells was measured in serial breast milk samples collected from 291 HIV-1-infected women in Nairobi, Kenya, by use of real-time DNA polymerase chain reaction amplification of BMCs. The number of infected BMCs per million cells was associated with levels of cell-free viral RNA in breast milk (R=.144; P=.032), levels of cell-free virus in blood plasma (R=.365; P<.001), and the detection of proviral DNA in cervical and vaginal secretions (P<.001 and P = .030, respectively). The number of infected BMCs per million cells was lower in colostrum or early milk than in mature milk (P<.001). Previous studies demonstrated that the concentration of BMCs varies throughout lactation, and we used these data to transform infected BMCs per million cells to infected BMCs per milliliter. The estimated concentration of infected BMCs per milliliter was higher in colostrum or early milk than in mature milk (P<.001). Each log10 increase in infected BMCs per milliliter was associated with a 3.19-fold-increased risk of transmission (P=.002), after adjustment for cell-free virus in plasma (hazard ratio [HR], 2.09; P=.03) and breast milk (HR, 1.01; P=1.00). This suggests that infected BMCs may play a more important role in transmission of HIV via breast-feeding than does cell-free virus.

Microbial-gut interactions in health and disease. Mucosal immune responses

The host gastrointestinal tract is exposed to countless numbers of foreign antigens and has embedded a unique and complex network of immunological and non-immunological mechanisms, often termed the gastrointestinal 'mucosal barrier', to protect the host from potentially harmful pathogens while at the same time 'tolerating' other resident microbes to allow absorption and utilization of nutrients. Of the many important roles of this barrier, it is the distinct responsibility of the mucosal immune system to sample and discriminate between harmful and beneficial antigens and to prevent entry of food-borne pathogens through the gastrointestinal (GI) tract. This system comprises an immunological network termed the gut-associated lymphoid tissue (GALT) that consists of unique arrangements of B cells, T cells and phagocytes which sample luminal antigens through specialized epithelia termed the follicle associated epithelia (FAE) and orchestrate co-ordinated molecular responses between immune cells and other components of the mucosal barrier. Certain pathogens have developed ways to bypass and/or withstand defence by the mucosal immune system to establish disease in the host. Some 'opportunistic' pathogens (such as Clostridium difficile) take advantage of host or other factors (diet, stress, antibiotic use) which may alter or weaken the response of the immune system. Other pathogens have developed mechanisms for invading gastrointestinal epithelium and evading phagocytosis/destruction by immune system defences. Once cellular invasion occurs, host responses are activated to limit local mucosal damage and repel the foreign influence. Some pathogens (Shigella spp, parasites and viruses) primarily establish localized disease while others (Salmonella, Yersinia, Listeria) use the lymphatic system to enter organs or the bloodstream and cause more systemic illness. In some cases, pathogens (Helicobacter pylori and Salmonella typhi) colonize the GI tract or associated lymphoid structures for extended periods of time and these persistent pathogens may also be potential triggers for other chronic or inflammatory diseases, including inflammatory bowel disease and malignancies. The ability of certain pathogens to avoid or withstand the host's immune assault and/or utilize these host responses to their own advantage (i.e. enhance further colonization) will dictate the pathogen's success in promoting illness and furthering its own survival.

Oral epithelial cells are susceptible to cell-free and cell-associated HIV-1 infection in vitro

Epithelial cells lining the oral cavity are exposed to HIV-1 through breast-feeding and oral-genital contact. Genital secretions and breast milk of HIV-1-infected subjects contain both cell-free and cell-associated virus. To determine if oral epithelial cells can be infected with HIV-1 we exposed gingival keratinocytes and adenoid epithelial cells to cell-free virus and HIV-1-infected peripheral blood mononuclear cells and monocytes. Using primary isolates we determined that gingival keratinocytes are susceptible to HIV-1 infection via cell-free CD4-independent infection only. R5 but not X4 viral strains were capable of infecting the keratinocytes. Further, infected cells were able to release infectious virus. In addition, primary epithelial cells isolated from adenoids were also susceptible to infection; both cell-free and cell-associated virus infected these cells. These data have potential implications in the transmission of HIV-1 in the oral cavity.

HIV-1 expression induces cyclin D1 expression and pRb phosphorylation in infected podocytes: cell-cycle mechanisms contributing to the proliferative phenotype in HIV-associated nephropathy

Background

The aberrant cell-cycle progression of HIV-1-infected kidney cells plays a major role in the pathogenesis of HIV-associated nephropathy, however the mechanisms whereby HIV-1 induces infected glomerular podocytes or infected tubular epithelium to exit quiescence are largely unknown. Here, we ask whether the expression of HIV-1 genes in infected podocytes induces cyclin D₁ and phospho-pRb (Ser780) expression, hallmarks of cyclin D1-mediated G₁ → S phase progression.

Results

We assessed cyclin D₁ and phospho-pRb (Ser780) expression in two well-characterized models of HIV-associated nephropathy pathogenesis: HIV-1 infection of cultured podocytes and HIV-1 transgenic mice (Tg26). Compared to controls, cultured podocytes expressing HIV-1 genes, and podocytes and tubular epithelium from hyperplastic nephrons in Tg26 kidneys, had increased levels of phospho-pRb (Ser780), a target of active cyclin D₁/cyclin-dependent kinase-4/6 known to promote G₁ → S phase progression. HIV-1-infected podocytes showed markedly elevated cyclin D₁ mRNA and cyclin D₁ protein, the latter of which did not down-regulate during cell-cell contact or differentiation, suggesting post-transcriptional stabilization of cyclin D₁ protein levels by HIV-1. The selective suppression of HIV-1 transcription by the cyclin-dependent kinase inhibitor, flavopiridol, abrogated cyclin D₁ expression, underlying the requirement for HIV-1 encoded products to induce cyclin D₁. Indeed, HIV-1 virus deleted of nef failed to induce cyclin D₁ mRNA to the level of other single gene mutant viruses.

Conclusions

HIV-1 expression induces cyclin D₁ and phospho-pRb (Ser780) expression in infected podocytes, suggesting that HIV-1 activates cyclin D1-dependent cell-cycle mechanisms to promote proliferation of infected renal epithelium.