Levelle D. Harris

Damaged intestinal epithelial integrity linked to microbial translocation in pathogenic simian immunodeficiency virus infections

The chronic phase of HIV infection is marked by pathological activation of the immune system, the extent of which better predicts disease progression than either plasma viral load or CD4+ T cell count. Recently, translocation of microbial products from the gastrointestinal tract has been proposed as an underlying cause of this immune activation, based on indirect evidence including the detection of microbial products and specific immune responses in the plasma of chronically HIV-infected humans or SIV-infected Asian macaques. We analyzed tissues from SIV-infected rhesus macaques (RMs) to provide direct in situ evidence for translocation of microbial constituents from the lumen of the intestine into the lamina propria and to draining and peripheral lymph nodes and liver, accompanied by local immune responses in affected tissues. In chronically SIV-infected RMs this translocation is associated with breakdown of the integrity of the epithelial barrier of the gastrointestinal (GI) tract and apparent inability of lamina propria macrophages to effectively phagocytose translocated microbial constituents. By contrast, in the chronic phase of SIV infection in sooty mangabeys, we found no evidence of epithelial barrier breakdown, no increased microbial translocation and no pathological immune activation. Because immune activation is characteristic of the chronic phase of progressive HIV/SIV infections, these findings suggest that increased microbial translocation from the GI tract, in excess of capacity to clear the translocated microbial constituents, helps drive pathological immune activation. Novel therapeutic approaches to inhibit microbial translocation and/or attenuate chronic immune activation in HIV-infected individuals may complement treatments aimed at direct suppression of viral replication.

Downregulation of Robust Acute Type I Interferon Responses Distinguishes Nonpathogenic Simian Immunodeficiency Virus (SIV) Infection of Natural Hosts from Pathogenic SIV Infection of Rhesus Macaques

ABSTRACT The mechanisms underlying the AIDS resistance of natural hosts for simian immunodeficiency virus (SIV) remain unknown. Recently, it was proposed that natural SIV hosts avoid disease because their plasmacytoid dendritic cells (pDCs) are intrinsically unable to produce alpha interferon (IFN-α) in response to SIV RNA stimulation. However, here we show that (i) acute SIV infections of natural hosts are associated with a rapid and robust type I IFN response in vivo, (ii) pDCs are the principal in vivo producers of IFN-α/β at peak acute infection in lymphatic tissues, and (iii) natural SIV hosts downregulate these responses in early chronic infection. In contrast, persistently high type I IFN responses are observed during pathogenic SIV infection of rhesus macaques.

CD4 downregulation by memory CD4+ T cells in vivo renders African green monkeys resistant to progressive SIVagm infection

African green monkeys (genus Chlorocebus) can be infected with species-specific simian immunodeficiency virus (SIVagm) but do not develop AIDS. These natural hosts of SIV, like sooty mangabeys, maintain high levels of SIV replication but have evolved to avoid immunodeficiency. Elucidating the mechanisms that allow natural hosts to coexist with SIV without overt disease may provide crucial information for understanding AIDS pathogenesis. Here we show that many CD4+ T cells from African green monkeys downregulate CD4 in vivo as they enter the memory pool; that downregulation of CD4 by memory T cells is independent of SIV infection; that the CD4− memory T cells maintain functions that are normally attributed to CD4+ T cells, including production of interleukin-2 (IL-2), production of IL-17, expression of forkhead box P3 and expression of CD40 ligand; that loss of CD4 expression protects these T cells from infection by SIVagm in vivo; and that these CD4− T cells can maintain major histocompatibility complex class II restriction. These data show that the absence of SIV-induced disease progression in natural host species may be partially explained by preservation of a subset of T cells that maintain CD4+ T cell function while being resistant to SIV infection in vivo.

Compromised gastrointestinal integrity in pigtail macaques is associated with increased microbial translocation, immune activation, and IL-17 production in the absence of SIV infection

Pigtail macaques (PTMs) rapidly progress to AIDS after simian immunodeficiency virus (SIV) infection. Given the strong association between human immunodeficiency virus (HIV) and SIV disease progression and microbial translocation and immune activation, we assessed whether high basal levels of immune activation and microbial translocation exist in PTMs. We found that before SIV infection, PTMs had high levels of microbial translocation that correlated with significant damage to the structural barrier of the gastrointestinal tract. Moreover, this increased microbial translocation correlated with high levels of immune activation and was associated with high frequencies of interleukin-17-producing T cells. These data highlight the relationship among mucosal damage, microbial translocation and systemic immune activation in the absence of SIV replication, and underscore the importance of microbial translocation in the rapid course of disease progression in SIV-infected PTMs. Furthermore, these data suggest that PTM may be an ideal model to study therapeutic interventions aimed at decreasing microbial translocation-induced immune activation.

Loss of mucosal CD103+ DCs and IL-17+ and IL-22+ lymphocytes is associated with mucosal damage in SIV infection.

Human immunodeficiency virus (HIV) and Simian immunodeficiency virus (SIV) disease progression is associated with multifocal damage to the gastrointestinal tract epithelial barrier that correlates with microbial translocation and persistent pathological immune activation, but the underlying mechanisms remain unclear. Investigating alterations in mucosal immunity during SIV infection, we found that damage to the colonic epithelial barrier was associated with loss of multiple lineages of interleukin (IL)-17-producing lymphocytes, cells that microarray analysis showed expressed genes important for enterocyte homeostasis, including IL-22. IL-22-producing lymphocytes were also lost after SIV infection. Potentially explaining coordinate loss of these distinct populations, we also observed loss of CD103+ dendritic cells (DCs) after SIV infection, which associated with the loss of IL-17- and IL-22-producing lymphocytes. CD103+ DCs expressed genes associated with promotion of IL-17/IL-22+ cells, and coculture of CD103+ DCs and naïve T cells led to increased IL17A and RORc expression in differentiating T cells. These results reveal complex interactions between mucosal immune cell subsets providing potential mechanistic insights into mechanisms of mucosal immune dysregulation during HIV/SIV infection, and offer hints for development of novel therapeutic strategies to address this aspect of AIDS virus pathogenesis.

Loss of CD103+ DCs and Mucosal IL-17+ and IL-22+ Lymphocytes is Associated with Mucosal Damage in SIV Infection

Human immunodeficiency virus (HIV) and Simian immunodeficiency virus (SIV) disease progression is associated with multifocal damage to the gastrointestinal tract epithelial barrier that correlates with microbial translocation and persistent pathological immune activation, but the underlying mechanisms remain unclear. Investigating alterations in mucosal immunity during SIV infection, we found that damage to the colonic epithelial barrier was associated with loss of multiple lineages of interleukin (IL)-17-producing lymphocytes, cells that microarray analysis showed expressed genes important for enterocyte homeostasis, including IL-22. IL-22-producing lymphocytes were also lost after SIV infection. Potentially explaining coordinate loss of these distinct populations, we also observed loss of CD103+ dendritic cells (DCs) after SIV infection, which associated with the loss of IL-17- and IL-22-producing lymphocytes. CD103+ DCs expressed genes associated with promotion of IL-17/IL-22+ cells, and coculture of CD103+ DCs and naïve T cells led to increased IL17A and RORc expression in differentiating T cells. These results reveal complex interactions between mucosal immune cell subsets providing potential mechanistic insights into mechanisms of mucosal immune dysregulation during HIV/SIV infection, and offer hints for development of novel therapeutic strategies to address this aspect of AIDS virus pathogenesis.

Reduced Inflammation and Lymphoid Tissue Immunopathology in Rhesus Macaques Receiving Anti–Tumor Necrosis Factor Treatment During Primary Simian Immunodeficiency Virus Infection

BACKGROUND Human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) infections induce robust, generalized inflammatory responses that begin during acute infection and lead to pathological systemic immune activation, fibrotic damage of lymphoid tissues, and CD4⁺ T-cell loss, pathogenic processes that contribute to disease progression. METHODS To better understand the contribution of tumor necrosis factor (TNF), a key regulator of acute inflammation, to lentiviral pathogenesis, rhesus macaques newly infected with SIVmac239 were treated for 12 weeks in a pilot study with adalimumab (Humira), a human anti-TNF monoclonal antibody. RESULTS Adalimumab did not affect plasma SIV RNA levels or measures of T-cell immune activation (CD38 or Ki67) in peripheral blood or lymph node T cells. However, compared with untreated rhesus macaques, adalimumab-treated rhesus macaques showed attenuated expression of proinflammatory genes, decreased infiltration of polymorphonuclear cells into the T-cell zone of lymphoid tissues, and weaker antiinflammatory regulatory responses to SIV infection (ie, fewer presumed alternatively activated [ie, CD163⁺] macrophages, interleukin 10-producing cells, and transforming growth factor β-producing cells), along with reduced lymphoid tissue fibrosis and better preservation of CD4⁺ T cells. CONCLUSIONS While HIV/SIV replication drives pathogenesis, these data emphasize the contribution of the inflammatory response to lentiviral infection to overall pathogenesis, and they suggest that early modulation of the inflammatory response may help attenuate disease progression.

CD4-Like Immunological Function by CD4− T Cells in Multiple Natural Hosts of Simian Immunodeficiency Virus

ABSTRACT Many species of African nonhuman primates are natural hosts for individual strains of simian immunodeficiency virus (SIV). These infected animals do not, however, develop AIDS. Here we show that multiple species of African nonhuman primate species characteristically have low frequencies of CD4+ T cells and high frequencies of both T cells that express only the alpha-chain of CD8 and double-negative T cells. These subsets of T cells are capable of eliciting functions generally associated with CD4+ T cells, yet these cells lack surface expression of the CD4 protein and are, therefore, poor targets for SIV in vivo. These data demonstrate that coevolution with SIV has, in several cases, involved downregulation of receptors for the virus by otherwise-susceptible host target cells. Understanding the genetic factors that lead to downregulation of these receptors may lead to therapeutic interventions that mimic this modulation in progressive infections.

Mechanisms underlying γδ T cell subset perturbations in SIV-infected Asian rhesus macaques

T cells that express the γδ T-cell receptor, which recognize microbial or stress-induced antigens, represent a minority of blood T cells but constitute a major proportion of intraepithelial lymphocytes in the gastrointestinal mucosa. As microbial products have been shown to translocate from the gastrointestinal tract into circulation in chronically HIV/Simian immunodeficiency virus (SIV)-infected individuals, we conducted a study of Vδ1 and Vδ2 T-cell frequency, phenotype, and function in blood, spleen, lymph nodes, gastrointestinal mucosa, and bronchoalveolar lavage of uninfected and chronically SIVsmE543-infected rhesus macaques (RMs). We found: (1) SIV-associated inversion of Vδ1/Vδ2 T cells occurs in blood and in several tissues; (2) γδ T cells are not infected by SIV in vivo; (3) the Vδ1/Vδ2 inversion involves expansion of Vδ1 T cells; (4) expanded Vδ1 T cells are phenotypically and functionally different from Vδ1 T cells from uninfected RMs; and (5) the stimulus underlying expansion of Vδ1 T cells appears to be microbial translocation. These data highlight the importance of microbial translocation-induced immune activation in chronically infected individuals and provide new insights into an immune dysregulation phenomenon that is a hallmark of HIV/SIV infection. These findings may lead to novel therapeutic interventions that improve the immune responses against microbial antigens, and thus, decrease microbial translocation-induced immune activation.

Loss of mucosal CD103|[plus]| DCs and IL-17|[plus]| and IL-22|[plus]| lymphocytes is associated with mucosal damage in SIV infection

Human immunodeficiency virus (HIV) and Simian immunodeficiency virus (SIV) disease progression is associated with multifocal damage to the gastrointestinal tract epithelial barrier that correlates with microbial translocation and persistent pathological immune activation, but the underlying mechanisms remain unclear. Investigating alterations in mucosal immunity during SIV infection, we found that damage to the colonic epithelial barrier was associated with loss of multiple lineages of interleukin (IL)-17-producing lymphocytes, cells that microarray analysis showed expressed genes important for enterocyte homeostasis, including IL-22. IL-22-producing lymphocytes were also lost after SIV infection. Potentially explaining coordinate loss of these distinct populations, we also observed loss of CD103+ dendritic cells (DCs) after SIV infection, which associated with the loss of IL-17- and IL-22-producing lymphocytes. CD103+ DCs expressed genes associated with promotion of IL-17/IL-22+ cells, and coculture of CD103+ DCs and naïve T cells led to increased IL17A and RORc expression in differentiating T cells. These results reveal complex interactions between mucosal immune cell subsets providing potential mechanistic insights into mechanisms of mucosal immune dysregulation during HIV/SIV infection, and offer hints for development of novel therapeutic strategies to address this aspect of AIDS virus pathogenesis.