Gut-associated lymphoid tissue (GALT) harbors the majority of T lymphocytes in the body

Salmonella typhimurium causes a localized enteric infection in immunocompetent individuals, whereas HIV-infected individuals develop a life-threatening bacteremia. Here we show that simian immunodeficiency virus (SIV) infection results in depletion of T helper type 17 (T H 17) cells in the ileal mucosa of rhesus macaques, thereby impairing mucosal barrier functions to S. typhimurium dissemination. In SIV-negative macaques, the gene expression profile induced by S. typhimurium in ligated ileal loops was dominated by T H 17 responses, including the expression of interleukin-17 (IL-17) and IL-22. T H 17 cells were markedly depleted in SIV-infected rhesus macaques, resulting in blunted T H 17 responses to S. typhimurium infection and increased bacterial dissemination. IL-17 receptor-deficient mice showed increased systemic dissemination of S. typhimurium from the gut, suggesting that IL-17 deficiency causes defects in mucosal barrier function. We conclude that SIV infection impairs the IL-17 axis, an arm of the mucosal immune response preventing systemic microbial dissemination from the gastrointestinal tract. A.G. served as consultant for the presentation of NTS bacteremia in African subjects. J.K.K. served as collaborator on studies with Il17ra −/− mice and provided useful comments on the experimental design. S.D. designed and supervised the SIV infections of rhesus macaques, blood sample scheduling, macaque protocols, processing and cell isolations for flow cytometry and DNA microarray analyses. A.J.B. was responsible for the experimental design and supervision of mouse studies, ligated ileal loop experiments in rhesus macaques, macaque protocols and analysis of host responses to Salmonella infection. A.J.B. collected tissue during the ligated ileal loop surgery and was responsible for the final manuscript preparation. A.J.B. and S.D. provided financial support for the study and equally contributed to the experimental design, supervision and data interpretation. Although nontyphoidal Salmonella serotypes (NTS) are common agents causing acute foodborne disease worldwide, it is unusual to isolate them from the blood of adults, because in immunocompetent individuals these pathogens remain localized to the intestine and cause a self-limiting gastroenteritis 1 . However, in people with underlying immunosuppression, NTS may spread beyond the intestine and reach the bloodstream, a serious complication known as NTS bacteremia2. The rise in the number of people with AIDS in sub-Saharan Africa has led to a dramatic increase in the frequency of NTS bacteremia3. In marked contrast to the pre-AIDS era4, NTS is currently a leading cause of hospital admission of adults and among the most common bacterial blood isolates from hospitalized adults in sub-Saharan Africa5, the vast majority of whom are HIV positive 3 . NTS infection in HIV-positive African adults is associated with high acute mortality rates (47%) 6 . Although the occurrence of NTS bacteremia in HIV-positive people is well documented, there are no reports inv...

Although the gut-associated lymphoid tissue (GALT) is an important early site for human immunodeficiency virus (HIV) replication and severe CD4؉ T-cell depletion, our understanding is limited about the restoration of the gut mucosal immune system during highly active antiretroviral therapy (HAART). We evaluated the kinetics of viral suppression, CD4؉ T-cell restoration, gene expression, and HIV-specific CD8 ؉ T-cell responses in longitudinal gastrointestinal biopsy and peripheral blood samples from patients initiating HAART during primary HIV infection (PHI) or chronic HIV infection (CHI) using flow cytometry, real-time PCR, and DNA microarray analysis. Viral suppression was more effective in GALT of PHI patients than CHI patients during HAART. Mucosal CD4 ؉ T-cell restoration was delayed compared to peripheral blood and independent of the time of HAART initiation. Immunophenotypic analysis showed that repopulating mucosal CD4 ؉ T cells were predominantly of a memory phenotype and expressed CD11␣, ␣ E ␤ 7 , CCR5, and CXCR4. Incomplete suppression of viral replication in GALT during HAART correlated with increased HIV-specific CD8 ؉ T-cell responses. DNA microarray analysis revealed that genes involved in inflammation and cell activation were up regulated in patients who did not replenish mucosal CD4 ؉ T cells efficiently, while expression of genes involved in growth and repair was increased in patients with efficient mucosal CD4 ؉ T-cell restoration. Our findings suggest that the discordance in CD4 ؉ T-cell restoration between GALT and peripheral blood during therapy can be attributed to the incomplete viral suppression and increased immune activation and inflammation that may prevent restoration of CD4 ؉ T cells and the gut microenvironment.

Human immunodeficiency virus (HIV) infection leads to severe CD4+ T-cell depletion in gut-associated lymphoid tissue (GALT) that persists despite the initiation of highly active antiretroviral therapy (HAART). It is not known whether restoration of gut mucosal CD4+ T cells and their functions is feasible during therapy and how that relates to immune correlates and viral reservoirs. Intestinal biopsies and peripheral blood samples from HIV-infected patients who were either HAART naive or on long-term HAART were evaluated. Our data demonstrated that gut CD4+ T-cell restoration ranged from modest (<50%) to high (>50%), compared with uninfected controls. Despite persistent CD4+ T-cell proviral burden and residual immune activation in GALT during HAART, effective CD4+ T-cell restoration (>50%) was achieved, which was associated with enhanced Th17 CD4+ T-cell accumulation and polyfunctional anti-HIV cellular responses. Our findings suggest that a threshold of>50% CD4+ T-cell restoration may be sufficient for polyfunctional HIV-specific T cells with implications in the evaluation of vaccines and therapeutics.

Gut-associated lymphoid tissue (GALT) is an early target for human immunodeficiency virus type 1 (HIV-1) infection and is a site for severe CD4؉ T-cell depletion. HIV-associated enteropathy is well-documented in chronic HIV-1 infection. However, the initial host responses to HIV infection in GALT and the early molecular correlates of HIV enteropathogenesis have not been characterized during primary HIV infection. In this study, we provide evidence of viral replication in GALT resident CD4؉ T cells and macrophages in primary-stage patients and identify early patterns of host mucosal responses and changes in the molecular microenvironment through gene expression profiling. High levels of viral replication in GALT and marked CD4 ؉ T-cell depletion correlated with decreased expression levels of genes regulating epithelial barrier maintenance and digestive/ metabolic functions. These changes coincided with a marked increase in the transcription of immune activation-, inflammation-, and apoptosis-associated genes. Our findings indicate that HIV-induced pathogenesis in GALT emerges at both the molecular and cellular levels prior to seroconversion in primary HIV infection, potentially setting the stage for disease progression by impairing the ability to control viral replication and repair and regenerate intestinal mucosal tissues.

Limited information is available on the molecular mechanisms by which long-term HIV-1-infected nonprogressors suppress HIV-1 infection and maintain immune functions. The intestinal mucosal immune system is an early target for HIV-1 infection and severe CD4 ؉ T cell depletion. We evaluated mucosal T lymphocyte subsets, virus-specific cellular responses, gene expression profiles, and viral loads in intestinal mucosal biopsies of long-term nonprogressor (LTNP) patients as compared to chronically HIV-1-infected patients with high viral loads (HVLs) and CD4 ؉ T cell loss, as well as HIV-seronegative healthy individuals. This study aims to identify the mucosal correlates of HIV disease progression and to determine the molecular changes associated with immune and intestinal dysfunction. LTNP patients had undetectable viral loads, normal CD4 ؉ T cell levels, and virus-specific cellular responses in peripheral blood and mucosal compartments. Microarray analysis revealed a significant increase in gene expression regulating immune activation, cell trafficking, and inflammatory response in intestinal mucosa of HVL patients as compared to LTNP patients. Genes associated with cell cycle regulation, lipid metabolism, and epithelial cell barrier and digestive functions were down-regulated in both HVL and LTNP patients. This may adversely influence nutrient adsorption and digestive functions, with the potential to impact the efficacy of antiretroviral therapy. We demonstrate that the maintenance of mucosal T cells, virus-specific responses, and distinct gene expression profiles correlate with clinical outcome in LTNP patients. However, the intestinal mucosal immune system remains an important target of HIV-1 infection in LTNP, and these effects may ultimately contribute toward disease progression.

Simian immunodeficiency virus (SIV) and human immunodeficiency virus (HIV) infections lead to rapid depletion of CD4؉ T cells from gut-associated lymphoid tissue (GALT). Although the administration of antiretroviral therapy (ART) has been shown to increase CD4 ؉ T-cell levels in the peripheral blood in both SIV and HIV infections, its efficacy in restoring intestinal mucosal CD4؉ T cells has not been well investigated. To gain insights into the molecular mechanisms of virally induced disruptions in the mucosal immune system, we have evaluated longitudinal changes in viral burden, T-cell subsets, and mucosal gene expression profiles in SIV-infected rhesus macaques in the absence or presence of ART. Our results demonstrate a dramatic suppression of mucosal viral loads and rapid reconstitution of CD4 ؉ T cells in GALT in animals receiving ART that were not observed in untreated SIV-infected animals. DNA microarray-based gene expression profiling indicated that CD4؉ T-cell restoration in GALT was associated with up regulation of growth factors and genes involved in repair and regeneration of the mucosal epithelium. In contrast, untreated SIV-infected animals increased expression of lymphocyte activation and inflammatory response-associated genes and did not up regulate mucosal growth and repair associated transcription. In conclusion, these data indicate that initiating ART in primary SIV infection may lead to the restoration of the mucosal immune system through reduction of inflammation and promotion of epithelial repair in the intestinal mucosa.

Gut-associated lymphoid tissue (GALT) is an early target of human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV