The mucosal barrier and immune activation in HIV pathogenesis

Faecal calprotectin in HIV-infected, HAART-naïve Ugandan children

OBJECTIVES

Calprotectin is a calcium- and zinc-binding protein and a marker in faeces of gastrointestinal inflammation. Reference values have been established in children older than 4 years. The aim of the present study was to determine the concentration of faecal calprotectin (FC) in human immunodeficiency virus (HIV)-infected, highly active antiretroviral therapy-naïve Ugandan children and compare it with the reference value.

METHODS

We tested 193 HIV-infected children ages 0 to 12 years in a hospital-based survey for FC. A standardised interview with sociodemographic information and medical history was used to assess risk factors. A cluster of differentiation 4 (CD4) cell percentage was prevalent in all of the children.

RESULTS

The median FC concentrations decreased with increasing age, as in healthy children. The median concentration was 208 mg/kg in infants 0 to 1 year, 171 mg/kg among toddlers 1 to 4 years, and 62 mg/kg for children 4 to 12 years. Children with advanced disease and a low CD4 cell percentage had significantly higher FC concentrations than those with a high CD4 cell percentage. Children older than 4 years with diarrhoea had significantly higher FC concentrations compared with those without diarrhoea.

CONCLUSIONS

HIV-infected children older than 4 years had a median FC concentration above the reference value, and gut inflammation in the children with elevated values is likely. Children with more advanced disease had increased FC concentrations regardless of age.

Thirty Years with HIV Infection-Nonprogression Is Still Puzzling: Lessons to Be Learned from Controllers and Long-Term Nonprogressors

In the early days of the HIV epidemic, it was observed that a minority of the infected patients did not progress to AIDS or death and maintained stable CD4+ cell counts. As the technique for measuring viral load became available it was evident that some of these nonprogressors in addition to preserved CD4+ cell counts had very low or even undetectable viral replication. They were therefore termed controllers, while those with viral replication were termed long-term nonprogressors (LTNPs). Genetics and virology play a role in nonprogression, but does not provide a full explanation. Therefore, host differences in the immunological response have been proposed. Moreover, the immunological response can be divided into an immune homeostasis resistant to HIV and an immune response leading to viral control. Thus, non-progression in LTNP and controllers may be due to different immunological mechanisms. Understanding the lack of disease progression and the different interactions between HIV and the immune system could ideally teach us how to develop a functional cure for HIV infection. Here we review immunological features of controllers and LTNP, highlighting differences and clinical implications.

Default in plasma and intestinal IgA responses during acute infection by simian immunodeficiency virus

BACKGROUND

Conflicting results regarding changes in mucosal IgA production or in the proportions of IgA plasma cells in the small and large intestines during HIV-infection have been previously reported. Except in individuals repeatedly exposed to HIV-1 but yet remaining uninfected, HIV-specific IgAs are frequently absent in mucosal secretions from HIV-infected patients. However, little is known about the organization and functionality of mucosal B-cell follicles in acute HIV/SIV infection during which a T-dependent IgA response should have been initiated. In the present study, we evaluated changes in B-cell and T-cell subsets as well as the extent of apoptosis and class-specific plasma cells in Peyer's Patches, isolated lymphoid follicles, and lamina propria. Plasma levels of IgA, BAFF and APRIL were also determined.

RESULTS

Plasma IgA level was reduced by 46% by 28 days post infection (dpi), and no IgA plasma cells were found within germinal centers of Peyer's Patches and isolated lymphoid follicles. This lack of a T-dependent IgA response occurs although germinal centers remained functional with no sign of follicular damage, while a prolonged survival of follicular CD4+ T-cells and normal generation of IgG plasma cells is observed. Whereas the average plasma BAFF level was increased by 4.5-fold and total plasma cells were 1.7 to 1.9-fold more numerous in the lamina propria, the relative proportion of IgA plasma cells in this effector site was reduced by 19% (duodemun) to 35% (ileum) at 28 dpi.

CONCLUSION

Our data provide evidence that SIV is unable to initiate a T-dependent IgA response during the acute phase of infection and favors the production of IgG (ileum) or IgM (duodenum) plasma cells at the expense of IgA plasma cells. Therefore, an early and generalized default in IgA production takes place during the acute of phase of HIV/SIV infection, which might impair not only the virus-specific antibody response but also IgA responses to other pathogens and vaccines as well. Understanding the mechanisms that impair IgA production during acute HIV/SIV infection is crucial to improve virus-specific response in mucosa and control microbial translocation.

Role of Human TRIM5α in Intrinsic Immunity

Human immunodeficiency virus (HIV) has a very narrow host range. HIV type 1 (HIV-1) does not infect Old World monkeys, such as the rhesus monkey (Rh). Rh TRIM5α was identified as a factor that confers resistance, intrinsic immunity, to HIV-1 infection. Unfortunately, human TRIM5α is almost powerless to restrict HIV-1. However, human TRIM5α potently restricts N-tropic murine leukemia viruses (MLV) but not B-tropic MLV, indicating that human TRIM5α represents the restriction factor previously designated as Ref1. African green monkey TRIM5α represents another restriction factor previously designated as Lv1, which restricts both HIV-1 and simian immunodeficiency virus isolated from macaque (SIVmac) infection. TRIM5 is a member of the tripartite motif family containing RING, B-box2, and coiled-coil domains. The RING domain is frequently found in E3 ubiquitin ligase, and TRIM5α is thought to degrade viral core via ubiquitin–proteasome-dependent and -independent pathways. The alpha isoform of TRIM5 has an additional C-terminal PRYSPRY domain, which is a determinant of species-specific retrovirus restriction by TRIM5α. On the other hand, the target regions of viral capsid protein (CA) are scattered on the surface of core. A single amino acid difference in the surface-exposed loop between α-helices 6 and 7 (L6/7) of HIV type 2 (HIV-2) CA affects viral sensitivity to human TRIM5α and was also shown to be associated with viral load in West African HIV-2 patients, indicating that human TRIM5α is a critical modulator of HIV-2 replication in vivo. Interestingly, L6/7 of CA corresponds to the MLV determinant of sensitivity to mouse factor Fv1, which potently restricts N-tropic MLV. In addition, human genetic polymorphisms also affect antiviral activity of human TRIM5α. Recently, human TRIM5α was shown to activate signaling pathways that lead to activation of NF-κB and AP-1 by interacting with TAK1 complex. TRIM5α is thus involved in control of viral infection in multiple ways.

The Microbiological Context of HIV Resistance: Vaginal Microbiota and Mucosal Inflammation at the Viral Point of Entry

Immune activation is increasingly recognized as a critical element of HIV infection and pathogenesis, causing expansion of virus founder populations at the mucosal port of entry and eventual exhaustion of cellular immune effectors. HIV susceptibility is well known to be influenced by concurrent sexually transmitted infections; however, the role of commensal vaginal microbiota is poorly characterized. Bacterial vaginosis (BV) is a risk factor for HIV acquisition in studies worldwide; however, the etiology of BV remains enigmatic, and the mechanisms by which BV increases HIV susceptibility are not fully defined. A model of how vaginal microbiota influences HIV transmission is considered in the context of a well-established cohort of HIV-exposed seronegative (HESN) commercial sex workers (CSW) in Nairobi, Kenya, many of whom have increased levels of anti-inflammatory factors in vaginal secretions and reduced peripheral immune activation (immune quiescence). Elucidation of the relationship between complex microbial communities and inflammatory mucosal responses underlying HIV infection should be a priority for future prevention-focussed research.

Evaluation of vitamin D levels among HIV-infected patients in New York City

Few studies have examined the vitamin D status in HIV-infected patients. A cross-sectional retrospective chart review of 2992 HIV-infected patients was conducted from 9/2008 to 5/2009. A total of 274 adult patients had 25-hydroxyvitamin D [25(OH)D] obtained by radioimmunoassay. None was receiving vitamin D (vitD) supplements. Vitamin D status was defined as the following: vitD deficiency (vitDd) as 25(OH)D <25 nmol/liter, vitD insufficiency (vitDi) as 25(OH)D 25-74 nmol/liter, and vitD optimal (vitDo) as 25(OH)D ≥75 nmol/liter. We analyzed demographic/laboratory data. vitDd, vitDi, and vitDo were 21.2% (58 patients, 58/274), 68.6% (188 patients, 188/274), and 10.2% (28 patients, 28/274), respectively. There were significant racial differences. Blacks were 60.3% (35 patients, 35/58), 40.4% (76 patients, 76/188), and 28.6 % (8 patients, 8/28) in vitDd, vitDi, and vitDo, respectively, p=0.002. CD4 T cell count was not different in these three groups. However, HIV viral load was significantly different. Median log (10) HIV viral load was 2.31 with IQR 1.70-409, 1.70 with IQR 1.70-2.96, and 1.70 with IQR 1.70-2.78 in vitDd, vitDi, and vitDo, respectively, p=0.039. Multivariate logistic regression analysis showed that black race [odd ratio (OR) 4.108, 95% confidence interval (CI) 1.462-11.543, p=0.007] and HIV viral load>50 copies/ml (OR 2.396, 95% CI 1.120-5.127, p=0.024) were significantly associated with vitamin D deficiency. Vitamin D deficiency was highly prevalent in HIV-infected patients. Detectable HIV viremia and dark skin (black ethnicity) were significantly associated with vitamin D deficiency. Evaluation of vitamin D status in HIV-infected patients should be considered and further studies are needed to define the effects of vitamin D.

Level of double negative T cells, which produce TGF-β and IL-10, predicts CD8 T-cell activation in primary HIV-1 infection

OBJECTIVE

Persistent immune activation plays a central role in the pathogenesis of HIV disease. Besides natural regulatory T cells (nTregs), 'double negative' T cells shown to exhibit regulatory properties could be involved in the control of harmful immune activation. The aim of this study was to analyze, in patients with primary HIV infection (PHI), the relationship between CD4(+)CD25(+)CD127(low)FoxP3(+) nTregs or CD3(+)CD4(-)CD8(-) double negative T cells and systemic immune activation.

DESIGN

A prospective longitudinal study of patients with early PHI.

METHODS

Twenty-five patients were included. Relationships between frequency of Treg subsets and T-cell activation, assessed on fresh peripheral blood mononuclear cells, were analyzed using nonparametric tests. Cytokine production by double negative T cells was assessed following anti-CD3/anti-CD28 stimulation.

RESULTS

No relationship was found between T-cell activation and frequencies of nTregs. In contrast, a strong negative relationship was found at baseline between the proportion of double negative T cells and the proportion of activated CD8 T cells coexpressing CD38 and HLA-DR (P = 0.005) or expressing Ki-67 (P = 0.002). In addition, the frequency of double negative T cells at baseline negatively correlated with the frequency of HLA-DR(+)CD38(+)CD8(+) T cells at month 6, defining the immune activation set point (P = 0.031). High proportions of stimulated double negative T cells were found to produce the immunosuppressive cytokines transforming growth factor-β1 and/or IL-10.

CONCLUSION

The proportion of double negative T cells at baseline was found to be predictive of the immune activation set point. Our data strongly suggest that double negative T cells may control immune activation in PHI. This effect might be mediated through the production of TGF-β1/IL-10 known to downmodulate immune activation.

Altered distribution of mucosal NK cells during HIV infection

The human gut mucosa is a major site of human immunodeficiency virus (HIV) infection and infection-associated pathogenesis. Increasing evidence shows that natural killer (NK) cells have an important role in control of HIV infection, but the mechanism(s) by which they mediate antiviral activity in the gut is unclear. Here, we show that two distinct subsets of NK cells exist in the gut, one localized to intraepithelial spaces (intraepithelial lymphocytes, IELs) and the other to the lamina propria (LP). The frequency of both subsets of NK cells was reduced in chronic infection, whereas IEL NK cells remained stable in spontaneous controllers with protective killer immunoglobulin-like receptor/human leukocyte antigen genotypes. Both IEL and LP NK cells were significantly expanded in immunological non-responsive patients, who incompletely recovered CD4+ T cells on highly active antiretroviral therapy (HAART). These data suggest that both IEL and LP NK cells may expand in the gut in an effort to compensate for compromised CD4+ T-cell recovery, but that only IEL NK cells may be involved in providing durable control of HIV in the gut.

Disease-modifying therapeutic concepts for HIV in the era of highly active antiretroviral therapy

Chronic HIV infection is associated with persistent immune activation and inflammation even among patients virologically suppressed on antiretroviral therapy for years. Chronic immune activation has been associated with poor outcomes--both AIDS-defining and non-AIDS-defining clinical events--and persistent CD4 T-cell depletion. The cause of chronic immune activation in well-controlled HIV infection is unknown. Proposed drivers include residual viral replication, microbial translocation, and coinfecting pathogens. Therapeutic interventions targeting immune activation are emerging, from approaches that interfere directly with activation and inflammatory pathways to those that prevent microbial translocation or decrease the availability of host target cells for the virus. In the context of the disappointing results of the interleukin-2 trials, the main challenges to developing these disease-modifying therapies include identifying an adequate target population and choosing surrogate endpoints that will provide positive proof-of-concept that the interventions will translate into long-term clinical benefit before embarking on large clinical endpoint trials.

Opioids and HIV/HCV infection

Since human immunodeficiency virus (HIV) and hepatitis C virus (HCV) share the same modes of transmission and common risk factors for infection, co-infections with HIV and HCV are frequently found in injection drug users (IDUs). IDUs represent one of the largest reservoirs of HIV as well as HCV in the United States. These two pathogens are also likely to be responsible for the highest infectious disease morbidity and mortality rates among IDUs. IDUs frequently involve the abuse of heroin, the most common abused opiate. Opiates have been suggested to have a cofactor role in the immunopathogenesis of HIV disease, as they have the potential to compromise host immune responses and enhances microbial infections. Although in vitro studies have yielded relatively agreeable data that morphine, the active metabolite of heroin, exacerbate HIV infection/replication, epidemiologic studies as well as in vivo non-human primate investigations on the impact of opiate abuse on HIV disease progression have yielded the conflicting data. Given immunomodulation and immunocompromising effect as well as demonstrated impact to enhance HIV replication in vitro, it is reasonable to believe that opiate abuse is a facilitator in HIV and/or HCV disease progression. However, much remain to be learned about the mechanisms of opiate-mediated broad influence on host immunity and viral expression. Thus, more extensive studies are needed in order to determine the effects of different conditions of opiate abuse and to define the understanding of the role of opiate in modulating HIV and/or HCV disease progression.

The role of IL-15 in challenging Acquired Immunodeficiency Syndrome

OBJECTIVE

To determine the functions of in vitro primed Natural Killer (NK) cells in Human Immunodeficiency Virus (HIV-1) infection and the role of IL-2, IL-12 and IL-15 in enhancing the NK survival and activity in terms of viral suppression and of purging of HIV provirus.

METHODS

Peripheral Blood Mononuclear Cells (PBMCs) and CD4+ T lymphocytes cells obtained from eight healthy donors were infected in vitro with HIV-1 and p24 was measured with and without IL-2, IL-12 and IL-15. We studied the effect of NK pulsed in vitro with IL-2, IL-12 and IL-15 on HIV replication by measurement of p-24 and DNA-provirus load when added into the culture of PBMCs and CD4+ T lymphocytes cells infected in vitro. We evaluated the effect of NK cells pulsed with IL-2, IL-12 and IL-15 on HIV replication and DNA-load into the culture of CD4+ T lymphocytes cells and PBMCs by trans-well chamber.

RESULTS

We found high levels of p24 in the supernatants of PBMCs and CD4+ T lymphocytes cells cultured with IL-2, IL-12, and IL-15. We observed a significant reduction of p24 in the culture both of infected PBMCs and CD4+ T lymphocytes cells in which was added NK pulsed with IL-15. We did not obtain the some results with NK pulsed with IL-2 and IL-12. We observed a power effect of NK pulsed with IL-15 on HIV-DNA. The trans-well chamber experiments showed that the effect of NK is both direct and both mediated by realizing of soluble factors.

CONCLUSIONS

This study highlights some important effects of IL 15 on NK in HIV patients anyway our results are preliminary and descriptive and others studies will be needed to provide rationale for immune therapies.

The gp41 epitope, QARVLAVERY, is highly conserved and a potent inducer of IgA that neutralizes HIV-1 and inhibits viral transcytosis

Mucosal surfaces are the predominant site of human immunodeficiency virus (HIV)-1 transmission. For prophylactic approaches to effectively prevent HIV infection and subsequent dissemination, the induction of mucosally relevant protective immunity will be critical. Here, we have characterized the antibody (Ab) response generated by a highly conserved gp41epitope, QARVLAVERY, in an optimized immunization model that elicits potent epitope-specific Abs in the serum, vaginal washes, and fecal secretions of immunized mice. Our results show that QARVLAVERY is indeed a potent inducer of IgA and importantly, QARVLAVERY-specific IgA was effective in neutralizing HIV and inhibiting viral transcytosis. Intriguingly, QARVLAVERY also generated an approximate 1:1 ratio of IgG:IgA in the serum of immunized mice, independent of the delivery regimen and produced early systemic IgA, even before IgG. In light of the significantly high IgA induction by QARVLAVERY and the functionality of epitope-specific Abs in the inhibition of HIV infection and transcytosis, QARVLAVERY is an attractive epitope to be considered in mucosal vaccination strategies against HIV.

Living in a house of cards: re-evaluating CD8+ T-cell immune correlates against HIV

The Merck STEP and the Thai RV144 human immunodeficiency virus (HIV) vaccine trials confirmed that we still have a long way to go before developing a prophylactic HIV vaccine. The main issue at hand is that we have yet to identify an immunological correlate of protection against HIV. While many question the T-cell-based approach towards vaccine development, it is likely that T cells will be a necessary part of any vaccine strategy. CD8(+) T cells remain an attractive option because of their ability to specifically recognize and eliminate virally infected host cells. In this review, we recapitulate the evidence for CD8(+) T cells as an immunological correlate against HIV, but more importantly, we assess the means by which we evaluate their antiviral capacity. To achieve a breakthrough in the domain of T-cell-based HIV vaccine development, it has become abundantly clear that we must overhaul our system of immune monitoring and come up with a 'rational' tactic to evaluate the efficacy of HIV-specific CD8(+) T cells.

Antibody and B-cell responses may control circulating lipopolysaccharide in patients with HIV infection

OBJECTIVES

To examine the relationship between plasma markers of microbial translocation and antibodies to lipopolysaccharide (LPS) and circulating memory B cells in patients with HIV infection.

DESIGN

Cross-sectional study in antiretroviral therapy (ART)-naive (n = 23) and ART-treated (n = 27) HIV patients.

METHODS

Antibodies to LPS and immunoglobulins, assayed in stored serum, and matched memory B-cell counts were correlated with levels of LPS and bacterial 16S ribosome DNA (16S rDNA), assayed in stored plasma.

RESULTS

In ART-naive patients, plasma LPS levels correlated inversely with serum levels of IgG and IgA antibodies to LPS (P = 0.03 and 0.006, respectively), serum levels of IgA anti-LPS correlated with total IgA (P < 0.0001) and levels of IgG anti-LPS correlated with IgM(+) memory B-cell counts (P = 0.025). In ART-treated patients, plasma LPS levels were not related to levels of LPS antibodies, but were related to CD4(+) T-cell and switched memory B-cell counts. There were no correlations with plasma levels of 16S rDNA.

CONCLUSION

Plasma LPS levels were associated with antibody and possibly B-cell responses to LPS in ART-naive HIV patients, whereas they were associated with the degree of immune reconstitution in ART-treated patients.

Strong viremia control in vaccinated macaques does not prevent gradual Th17 cell loss from central memory

It has been proposed that microbial translocation might play a role in chronic immune activation during HIV/SIV infection. Key roles in fighting bacterial and fungal infections have been attributed to Th17 and Tc17 cells. Th17 cells can be infected with HIV/SIV, however whether effective vaccination leads to their maintenance following viral challenge has not been addressed. Here we retrospectively investigated if a vaccine regimen that potently reduced viremia post-challenge preserved Th17 and Tc17 cells, thus adding benefit in the absence of sterilizing protection. Rhesus macaques were previously vaccinated with replication-competent Adenovirus recombinants expressing HIVtat and HIVenv followed by Tat and gp140 protein boosting. Upon SHIV(89.6P) challenge, the vaccines exhibited a significant 4 log reduction in chronic viremia compared to sham vaccinated controls which rapidly progressed to AIDS [39]. Plasma and cryopreserved PBMC samples were examined pre-challenge and during acute and chronic infection. Control macaques exhibited a rapid loss of CD4(+) cells, including Th17 cells. Tc17 cells tended to decline over the course of infection although significance was not reached. Immune activation, assessed by Ki-67 expression, was associated with elevated chronic viremia of the controls. Significantly increased plasma IFN-γ levels were also observed. No increase in plasma LPS levels were observed suggesting a lack of microbial translocation. In contrast, vaccinated macaques had no evidence of immune activation within the chronic phase and preserved both CD4(+) T-cells and Tc17 cells in PBMC. Nevertheless, they exhibited a gradual, significant loss of Th17 cells which concomitantly displayed significantly higher CCR6 expression over time. The gradual Th17 cell decline may reflect mucosal homing to inflammatory sites and/or slow depletion due to ongoing low levels of SHIV replication. Our results suggest that potent viremia reduction during chronic SHIV infection will delay but not prevent the loss of Th17 cells.

Acute HIV-1 Infection

In 2009, the United Nations Estimated that 33.2 Million People worldwide were living with human immunodeficiency virus type 1 (HIV-1) infection and that 2.6 million people had been newly infected. The need for effective HIV-1 prevention has never been greater. In this review, we address recent critical advances in our understanding of HIV-1 transmission and acute HIV-1 infection. Fourth-generation HIV-1 testing, now available worldwide,^, will allow the diagnosis of infection in many patients and may lead to new treatments and opportunities for prevention.

Biomedical differences between human and nonhuman hominids: potential roles for uniquely human aspects of sialic acid biology

Although humans are genetically very similar to the evolutionarily related nonhuman hominids (chimpanzees, bonobos, gorillas, and orangutans), comparative studies suggest a surprising number of uniquely human differences in the incidence and/or severity of biomedical conditions. Some differences are due to anatomical changes that occurred during human evolution. However, many cannot be explained either by these changes or by known environmental factors. Because chimpanzees were long considered models for human disease, it is important to be aware of these differences, which appear to have been deemphasized relative to similarities. We focus on the pathophysiology and pathobiology of biomedical conditions that appear unique to humans, including several speculative possibilities that require further study. We pay particular attention to the possible contributions of uniquely human changes in the biology of cell-surface sialic acids and the proteins that recognize them. We also discuss the metabolic incorporation of a diet-derived nonhuman sialic acid, which generates a novel xeno-autoantigen reaction, and chronic inflammation known as xenosialitis.

Enhancement of replication of RNA viruses by ADAR1 via RNA editing and inhibition of RNA-activated protein kinase

Adenosine deaminase acting on RNA 1 (ADAR1) is a double-stranded RNA binding protein and RNA-editing enzyme that modifies cellular and viral RNAs, including coding and noncoding RNAs. This interferon (IFN)-induced protein was expected to have an antiviral role, but recent studies have demonstrated that it promotes the replication of many RNA viruses. The data from these experiments show that ADAR1 directly enhances replication of hepatitis delta virus, human immunodeficiency virus type 1, vesicular stomatitis virus, and measles virus. The proviral activity of ADAR1 occurs through two mechanisms: RNA editing and inhibition of RNA-activated protein kinase (PKR). While these pathways have been found independently, the two mechanisms can act in concert to increase viral replication and contribute to viral pathogenesis. This novel type of proviral regulation by an IFN-induced protein, combined with some antiviral effects of hyperediting, sheds new light on the importance of ADAR1 during viral infection and transforms our overall understanding of the innate immune response.

Inflammation and epithelial cell injury in AIDS enteropathy: involvement of endoplasmic reticulum stress

Immunosuppressive lentivirus infections, including human, simian, and feline immunodeficiency viruses (HIV, SIV, and FIV, respectively), cause the acquired immunodeficiency syndrome (AIDS), frequently associated with AIDS enteropathy. Herein, we investigated the extent to which lentivirus infections affected mucosal integrity and intestinal permeability in conjunction with immune responses and activation of endoplasmic reticulum (ER) stress pathways. Duodenal biopsies from individuals with HIV/AIDS exhibited induction of IL-1β, CD3ε, HLA-DRA, spliced XBP-1(Xbp-1s), and CHOP expression compared to uninfected persons (P<0.05). Gut epithelial cells exposed to HIV-1 Vpr demonstrated elevated TNF-α, IL-1β, spliced Xbp-1s, and CHOP expression (P<0.05) together with calcium activation and disruption of epithelial cell monolayer permeability. In addition to reduced blood CD4(+) T lymphocyte levels, viral loads in the gut and plasma were high in FIV-infected animals (P<0.05). FIV-infected animals also exhibited a failure to gain weight and increased lactulose/mannitol ratios compared with uninfected animals (P<0.05). Proinflammatory and ER stress gene expression were activated in the ileum of FIV-infected animals (P<0.05), accompanied by intestinal epithelial damage with loss of epithelial cells and leukocyte infiltration of the lamina propria. Lentivirus infections cause gut inflammation and ensuing damage to intestinal epithelial cells, likely through induction of ER stress pathways, resulting in disruption of gut functional integrity.

Mutiny or scrutiny: NK cell modulation of DC function in HIV-1 infection

Accumulating data suggest that natural killer (NK) cells are involved not only in the innate antiviral response following infection, but also in shaping the quality of the adaptive immune response by modulating the functional properties of myeloid dendritic cells (DC) during the acute immune response to infection. In this role, NK cells ensure that only fully mature, immunogenic DCs gain access to inductive sites, where they might prime effective antiviral adaptive immune responses. However, increasing evidence now suggests that several aspects of this cross-talk between NK cells and DCs are compromised during HIV infection, potentially contributing to immune dysfunction.

HIV-1 envelope, integrins and co-receptor use in mucosal transmission of HIV

It is well established that HIV-1 infection typically involves an interaction between the viral envelope protein gp120/41 and the CD4 molecule followed by a second interaction with a chemokine receptor, usually CCR5 or CXCR4. In the early stages of an HIV-1 infection CCR5 using viruses (R5 viruses) predominate. In some viral subtypes there is a propensity to switch to CXCR4 usage (X4 viruses). The receptor switch occurs in ~ 40% of the infected individuals and is associated with faster disease progression. This holds for subtypes B and D, but occurs less frequently in subtypes A and C. There are several hypotheses to explain the preferential transmission of R5 viruses and the mechanisms that lead to switching of co-receptor usage; however, there is no definitive explanation for either. One important consideration regarding transmission is that signaling by R5 gp120 may facilitate transmission of R5 viruses by inducing a permissive environment for HIV replication. In the case of sexual transmission, infection by HIV requires the virus to breach the mucosal barrier to gain access to the immune cell targets that it infects; however, the immediate events that follow HIV exposure at genital mucosal sites are not well understood. Upon transmission, the HIV quasispecies that is replicating in an infected donor contracts through a “genetic bottleneck”, and often infection results from a single infectious event. Many details surrounding this initial infection remain unresolved. In mucosal tissues, CD4⁺ T cells express high levels of CCR5, and a subset of these CD4⁺/CCR5^high cells express the integrin α₄β₇, the gut homing receptor. CD4⁺/CCR5^high/ α4β7^high T cells are highly susceptible to infection by HIV-1 and are ideal targets for an efficient productive infection at the point of transmission. In this context we have demonstrated that the HIV-1 envelope protein gp120 binds to α₄β₇ on CD4⁺ T cells. On CD4⁺/CCR5^high/ α4β7^high T cells, α₄β₇ is closely associated with CD4 and CCR5. Furthermore, α₄β₇ is ~3 times the size of CD4 on the cell surface, that makes it a prominent receptor for an efficient virus capture. gp120-α₄β₇ interactions mediate the activation of the adhesion-associated integrin LFA-1. LFA-1 facilitates the formation of virological synapses and cell-to-cell spread of HIV-1. gp120 binding to α₄β₇ is mediated by a tripeptide located in the V1/V2 domain of gp120. Of note, the V1/V2 domain of gp120 has been linked to variations in transmission fitness among viral isolates raising the intriguing possibility that gp120-α₄β₇ interactions may be linked to transmission fitness. Although many details remain unresolved, we hypothesize that gp120-α₄β₇ interactions play an important role in the very early events following sexual transmission of HIV and may have important implication in the design of vaccine strategies for the prevention of acquisition of HIV infection

Rapid rise in detection of human papillomavirus (HPV) infection soon after incident HIV infection among South African women

BACKGROUND

It is well established that the prevalence of human papillomavirus (HPV) infection is increased among human immunodeficiency virus (HIV)-positive individuals, but the temporal relationships between these infections are unclear.

METHODS

During a South African cervical cancer screening trial, 5595 women 35-65 years of age were followed up for 36 months; 577 women were HIV positive at enrollment, HIV seroconversion occurred in 123 women, and 4895 women remained HIV negative throughout. Tests for high-risk HPV DNA and cytology were performed on cervical samples, and a colposcopy/biopsy was performed at each visit. The effects of early HIV infection on the risk of HPV infection and HPV-related disease were evaluated.

RESULTS

Among seroconverters, HPV infection prevalence was 20.3% before seroconversion, 23.6% at seroconversion (P = .4), and 49.1% after seroconversion (P = .01). Seroconverters had significantly lower HPV infection prevalence than women with prevalent HIV infection before and at seroconversion (41.8% and 45.9%, respectively) but had similar HPV infection prevalence to women with prevalent HIV infection after seroconversion (49.4%). HIV seroconversion was associated with newly detected HPV infection (adjusted hazard ratio [AHR], 4.02; 95% confidence interval [CI], 2.26-7.13) and increased risk of low-grade cytological abnormalities (AHR, 2.53; 95% CI, 1.16-5.51) compared with HIV-negative women.

CONCLUSION

Detection of HPV infection increases rapidly within the first years after HIV seroconversion, suggesting that mucosal immune dysfunction occurring at an early stage of HIV infection may influence HPV-related diseases.

HIV protease inhibitors induce endoplasmic reticulum stress and disrupt barrier integrity in intestinal epithelial cells

The integrity of the intestinal epithelial barrier plays a crucial role in maintaining symbiotic homeostasis between microbes in the gut lumen and eukaryotic cells. Disruption of intestinal epithelial barrier function occurs commonly under various pathological conditions, including trauma, inflammatory bowel disease, and drug-induced gastrointestinal toxicity, exhibiting increased intestinal epithelial paracellular permeability or "leakiness" of the intestinal mucosa. Endoplasmic reticulum (ER) stress has recently been linked to various pathological conditions, including intestinal inflammation. Our previous studies have shown that HIV protease inhibitors (PIs) induce ER stress and activate the unfolded protein response (UPR) in different types of cells, and HIV PI-induced UPR activation contributes to the disruption of barrier function in intestinal epithelial cells and the increase of intestinal permeability. This chapter will discuss the commonly used methods for analysis of ER stress activation and epithelial barrier function. Both in vitro cell culture models and in vivo animal models are useful tools to examine general drug-induced ER stress and intestinal barrier dysfunction.

HLA/KIR restraint of HIV: surviving the fittest

Multiple epidemiological studies have demonstrated associations between the human leukocyte antigen (HLA) loci and human immunodeficiency virus (HIV) disease, and more recently the killer cell immunoglobulin-like (KIR) locus has been implicated in differential responses to the virus. Genome-wide association studies have convincingly shown that the HLA class I locus is the most significant host genetic contributor to the variation in HIV control, underscoring a central role for CD8 T cells in resistance to the virus. However, both genetic and functional data indicate that part of the HLA effect on HIV is due to interactions between KIR and HLA genes, also implicating natural killer cells in defense against viral infection and viral expansion prior to initiation of an adaptive response. We review the HLA and KIR associations with HIV disease and the progress that has been made in understanding the mechanisms that explain these associations.

Good cell, bad cell: flow cytometry reveals T-cell subsets important in HIV disease

Flow cytometry is a key technology in the study of HIV disease. In this article, we review various cellular markers that can be measured in the setting of pathogenesis or vaccination studies, including markers of activation, differentiation, senescence, immune suppression, and function. In addition, we discuss important considerations for making these measurements. Finally, we examine how flow cytometry studies have taught researchers about the disease process, and the potential for flow cytometry technology to guide treatment decisions and evaluate vaccine candidates in the future.

Th17 cells, HIV and the gut mucosal barrier

PURPOSE OF REVIEW

We will present recent studies on a subset of CD4 T helper cells, Th17 cells, that appears to be critical for regulating gut mucosal immune responses against extracellular microbial pathogens and may serve as a link between innate and adaptive immune responses. Implications of the loss of Th17 CD4 T cells in HIV infection will be discussed in relation to the chronic immune activation and HIV pathogenesis.

RECENT FINDINGS

Severe depletion of CD4 T cells occurs in the gut mucosa during primary HIV and simian immunodeficiency virus infections. A pronounced loss of mucosal Th17 CD4 T cells in the simian immunodeficiency virus-infected rhesus macaque model of AIDS is linked to impaired immune responses in the gut mucosa to an enteric pathogen, Salmonella typhimurium, leading to the lack of local control of the pathogen and its translocation. Recovery of the gut mucosal immune system during highly active antiretroviral therapy is slow and incomplete compared with the peripheral blood compartment. Recent studies suggest that the replenishment of Th17 CD4 T cells in the gut mucosa during highly active antiretroviral therapy, or during nonpathogenic simian immunodeficiency virus infections in the nonhuman primate models, correlates with better restoration and function of the gut mucosal immune system.

SUMMARY

A better understanding of the role of Th17 CD4 cells in the generation of mucosal immune responses to enteric pathogens and maintenance of the intestinal epithelial integrity in HIV-infected patients will help in the development of novel strategies to modulate and enhance mucosal immune system and its function.

Immune activation, apoptosis, and Treg activity are associated with persistently reduced CD4+ T-cell counts during antiretroviral therapy

BACKGROUND

Persistently reduced CD4(+) T-lymphocyte counts in the face of undetectable HIV viremia are seen in a sizable percentage of HIV-infected patients undergoing antiretroviral therapy (ART). We analyzed the immune correlates of this phenomenon.

MATERIALS AND METHODS

Sixty-seven HIV-infected patients with undetectable viremia (<50 copies/microl) after more than 7 years of ART were enrolled in the study and divided into two groups (CD4 cell counts >500 cells/microl or <500 cells/microl). Duration of HIV infection (>16 years) was comparable. Peripheral blood mononuclear cell were stimulated with gag+env or with cytomegalovirus peptides. Activated T cells (Ki67(+)), Treg lymphocytes (CD4(+)/CD25high/Foxp3+), divided into naive and activated cells based on PD1 expression, interleukin (IL)-10 and transforming growth factor (TGF)-beta production, annexin V, activation of caspases 8 and 9, Toll-like receptor (TLR)2 and TLR4 expression on immune cells, and plasma lipopolysaccharide (LPS) concentration were analyzed.

RESULTS

CD4(+)/Ki67(+) T cells; plasma LPS; total, naive, and activated Treg; TLR2-expressing and TLR4-expressing Treg; IL-10 production; and early and late apoptotic CD4 T cells, were significantly increased in patients with undetectable viremia and CD4 cell counts less than 500 cells/microl after more than 7 years of ART. As previously shown, CD4 nadir were also lower in these individuals. Immune activation, LPS concentration, Treg, and degree of apoptosis were negatively correlated with CD4 cell counts.

CONCLUSION

Lack of CD4 recovery in individuals in whom ART suppresses HIV replication is associated with complex immune alterations. Immune activation, likely driven by altered gut permeability and resulting in augmented Treg activity could play a pivotal role in this process.

Nonprogressive and progressive primate immunodeficiency lentivirus infections

Natural hosts for simian immunodeficiency virus (SIV) can be, and are often naturally, infected with species-specific SIVs, but do not develop acquired immunodeficiency syndrome (AIDS). These natural hosts maintain high SIV viral loads, but avoid immunodeficiency. Elucidating the mechanisms that allow natural hosts to coexist with SIV without overt disease may provide crucial information for understanding AIDS pathogenesis. Over the past few years, several key features of natural SIV infections have been described in studies conducted predominantly in sooty mangabeys (SMs), African green monkeys (AGMs), and mandrills. Natural SIV hosts are able to avoid the chronic, generalized immune system activation that is associated with disease progression in HIV-infected individuals and are known to downmodulate the expression of the receptors for SIV. In this perspective we propose that a critical factor that differentiates nonprogressive from progressive HIV or SIV infection is the maintenance of T cell immune competence in the face of a virus that infects and kills CD4(+) T cells. Elucidation of the mechanisms underlying the preservation of immune function during and after the acute phase of natural SIV infection may lead to the design of novel preventive and therapeutic interventions for treatment of chronic HIV infection.

Innate immune recognition and activation during HIV infection

The pathogenesis of HIV infection, and in particular the development of immunodeficiency, remains incompletely understood. Whichever intricate molecular mechanisms are at play between HIV and the host, it is evident that the organism is incapable of restricting and eradicating the invading pathogen. Both innate and adaptive immune responses are raised, but they appear to be insufficient or too late to eliminate the virus. Moreover, the picture is complicated by the fact that the very same cells and responses aimed at eliminating the virus seem to play deleterious roles by driving ongoing immune activation and progressive immunodeficiency. Whereas much knowledge exists on the role of adaptive immunity during HIV infection, it has only recently been appreciated that the innate immune response also plays an important part in HIV pathogenesis. In this review, we present current knowledge on innate immune recognition and activation during HIV infection based on studies in cell culture, non-human primates, and HIV-infected individuals, and discuss the implications for the understanding of HIV immunopathogenesis.

The route of inoculation determines the tissue tropism of modified vaccinia Tiantan expressing the spike glycoprotein of SARS-CoV in mice

The live replication‐competent modified vaccinia virus Tiantan (MVTT) is an attractive vaccine vector, yet little is known about its tissue tropism and pathology in vivo. Recently, we demonstrated that a recombinant MVTT expressing the spike glycoprotein of SARS‐CoV (namely MVTT‐S) is superior to the non‐replicating modified vaccinia Ankara (MVA‐S) for inducing high level of neutralizing antibodies through mucosal vaccination. In this study, we further determined the tissue tropism and safety of MVTT‐S after the vaccine was administrated through various routes including: intramuscular (i.m.), intranasal (i.n.), and intravaginal (i.vag.) inoculations, respectively. Using real‐time PCR, nested PCR, immunohistochemistry and in situ hybridization assays, we found that MVTT‐S was able to produce a transient infection in all cases within 48 hr post‐inoculation, yet the major site of viral replication in various tissues or organs was dependent on the route of viral administration. We demonstrated that i.m. injection of MVTT‐S primarily targeted draining inguinal lymph nodes, whereas mucosal inoculation had broader range of tissue infections. i.n. inoculation involved infections in lungs, kidneys, spleens and cervix lymph nodes while i.vag. administration targeted uteruses, ovaries, kidneys and spleens. Critically, the infection did not cause severe pathogenic consequences in infected tissues, which was consistent to the attenuated phenotype of MVTT‐S. Our findings have implications for the optimization of vaccination route and for studies on the correlation between the magnitude of immune responses and the extent of tissue involvement in vivo. J. Med. Virol. 82: 727–734, 2010. © 2010 Wiley‐Liss, Inc.

Exposure to HIV-1 directly impairs mucosal epithelial barrier integrity allowing microbial translocation

While several clinical studies have shown that HIV-1 infection is associated with increased permeability of the intestinal tract, there is very little understanding of the mechanisms underlying HIV-induced impairment of mucosal barriers. Here we demonstrate that exposure to HIV-1 can directly breach the integrity of mucosal epithelial barrier, allowing translocation of virus and bacteria. Purified primary epithelial cells (EC) isolated from female genital tract and T84 intestinal cell line were grown to form polarized, confluent monolayers and exposed to HIV-1. HIV-1 X4 and R5 tropic laboratory strains and clinical isolates were seen to reduce transepithelial resistance (TER), a measure of monolayer integrity, by 30–60% following exposure for 24 hours, without affecting viability of cells. The decrease in TER correlated with disruption of tight junction proteins (claudin 1, 2, 4, occludin and ZO-1) and increased permeability. Treatment of ECs with HIV envelope protein gp120, but not HIV tat, also resulted in impairment of barrier function. Neutralization of gp120 significantly abrogated the effect of HIV. No changes to the barrier function were observed when ECs were exposed to Env defective mutant of HIV. Significant upregulation of inflammatory cytokines, including TNF-α, were seen in both intestinal and genital epithelial cells following exposure to HIV-1. Neutralization of TNF-α reversed the reduction in TERs. The disruption in barrier functions was associated with viral and bacterial translocation across the epithelial monolayers. Collectively, our data shows that mucosal epithelial cells respond directly to envelope glycoprotein of HIV-1 by upregulating inflammatory cytokines that lead to impairment of barrier functions. The increased permeability could be responsible for small but significant crossing of mucosal epithelium by virus and bacteria present in the lumen of mucosa. This mechanism could be particularly relevant to mucosal transmission of HIV-1 as well as immune activation seen in HIV-1 infected individuals.

Clinical studies have shown that HIV-1 infected patients have increased intestinal permeability. In chronically infected patients that progress to AIDS, there is activation of immune cells consistent with leakage of microbes via the gut. However, the mechanism by which this occurs is not clear. Here, we show that direct exposure of intestinal and genital epithelial cells to HIV leads to breaching of the mucosal barrier and increased leakage of both bacteria and virus across the epithelium. The mechanism of this breakdown appears to be due to inflammatory factors produced by epithelial cells themselves, in response to HIV-1 exposure, that destroy the tight junctions between epithelial cells, thereby allowing microbes access to the inside of the body. Interestingly, we found that treatment of epithelial cells with just the surface glycoprotein from HIV could lead to similar breakdown of the barrier. This implies that when mucosal epithelial cells come in direct contact with large amounts of HIV-1, the virus can cross into the inside of the body and cause direct infection of target cells. The crossing of the bacteria by similar mechanism can lead to chronic inflammation and activation of immune cells of the body.

A steady state of CD4+ T cell memory maturation and activation is established during primary subtype C HIV-1 infection

The functional integrity of CD4(+) T cells is crucial for well-orchestrated immunity and control of HIV-1 infection, but their selective depletion during infection creates a paradox for understanding a protective response. We used multiparameter flow cytometry to measure activation, memory maturation, and multiple functions of total and Ag-specific CD4(+) T cells in 14 HIV-1- and CMV- coinfected individuals at 3 and 12 mo post HIV-1 infection. Primary HIV-1 infection was characterized by elevated levels of CD38, HLA-DR, and Ki67 in total memory and Gag-specific CD4(+) and CD8(+) T cells. In both HIV-infected and 15 uninfected controls, the frequency of activated cells was uniformly distributed among early differentiated (ED; CD45RO(+)CD27(+)), late differentiated (CD45RO(+)CD27(-)), and fully differentiated effector (CD45RO(-)CD27(-)) memory CD4(+) T cells. In HIV-1-infected individuals, activated CD4(+) T cells significantly correlated with viremia at 3 mo postinfection (r = 0.79, p = 0.0007) and also harbored more gag provirus DNA copies than nonactivated cells (p = 0.04). Moreover, Gag-specific ED CD4(+) T cells inversely associated with plasma viral load (r = -0.87, p < 0.0001). Overall, we show that low copy numbers of gag provirus and plasma RNA copies associated with low CD4 activation as well as accumulation of ED HIV-specific CD4(+) memory. Significant positive correlations between 3 and 12 mo activation and memory events highlighted that a steady state of CD4(+) T cell activation and memory maturation was established during primary infection and that these cells were unlikely to be involved in influencing the course of viremia in the first 12 mo of HIV-1 infection.

Latent cytomegalovirus infection exacerbates experimental colitis

Inflammatory bowel disease (IBD) severity is positively correlated with cytomegalovirus (CMV) infection. This may reflect CMV triggering and/or exacerbating flares of IBD and/or IBD or immunosuppressive drugs administered to patients with IBD increasing susceptibility to CMV infection. Herein, we performed studies in mice to investigate these possibilities. Mice administered murine CMV (MCMV) developed signs of acute viral infection (malaise and weight loss) and had MCMV loads that were readily detected in numerous organs including the intestine. By 4 weeks, these mice manifested a "latent" infection in which MCMV levels were low but detectable by PCR. Such MCMV infection did not induce acute colitis in either wild-type mice or IL-10(-/-) mice, which are highly prone to developing colitis. However, underlying MCMV infection in an acute or latent state exacerbated the severity of colitis induced by dextran sodium sulfate (DSS). Such potentiation of DSS colitis by latent MCMV infection seemed to occur without viral reactivation. Whereas initial MCMV infection induced acute alterations in serum and intestinal cytokines, such cytokine levels returned to baseline before administration of DSS. However, the initial infection resulted in lasting elevation of antibodies to commensal bacterial antigens, suggesting that MCMV infection may have potentiated colitis via priming of the intestinal immune response to gut microbiota. Thus, underlying CMV infection can alter mucosal immunity, potentially increasing the tendency of CMV-infected hosts to develop colitis.

Manifestations and management of lymphogranuloma venereum

PURPOSE OF REVIEW

This review was prompted by a sustained outbreak of lymphogranuloma venereum that has been observed among men who have sex with men (MSM) worldwide since 2004. Recent developments in the epidemiology, diagnosis and management of the infection are summarized.

RECENT FINDINGS

Between the early 1980s and 2003, lymphogranuloma venereum was rarely seen in the developed world. In 2003, a cluster of cases was seen in the Netherlands occurring mostly in HIV-positive MSM with high levels of sexual risk. With the assistance of novel molecular diagnostic techniques, more than a thousand cases of Chlamydia trachomatis L2 serovar disease have now been reported in MSM worldwide. Almost all have presented with rectal infection, usually manifesting as severe proctitis, with ulcer adenopathy syndrome seldom seen. Oral doxycycline remains the recommended treatment and has proven effective in the recent outbreak. Conflicting data exist regarding the prevalence of asymptomatic infection, and our understanding of the exact modes of transmission remains incomplete.

SUMMARY

Lymphogranuloma venereum appears to have reestablished endemicity among MSM populations in many industrialized nations. In the relative absence of recent publications from its traditional endemic regions it can be assumed that these populations remain afflicted by the infection as well.