Mucosal atrophy is associated with loss of activated T cells in the duodenal mucosa of human immunodeficiency virus (HIV)-infected patients

The Hitchhiker Guide to CD4+ T-Cell Depletion in Lentiviral Infection. A Critical Review of the Dynamics of the CD4+ T Cells in SIV and HIV Infection

CD4⁺ T-cell depletion is pathognomonic for AIDS in both HIV and simian immunodeficiency virus (SIV) infections. It occurs early, is massive at mucosal sites, and is not entirely reverted by antiretroviral therapy (ART), particularly if initiated when T-cell functions are compromised. HIV/SIV infect and kill activated CCR5-expressing memory and effector CD4⁺ T-cells from the intestinal lamina propria. Acute CD4⁺ T-cell depletion is substantial in progressive, nonprogressive and controlled infections. Clinical outcome is predicted by the mucosal CD4⁺ T-cell recovery during chronic infection, with no recovery occurring in rapid progressors, and partial, transient recovery, the degree of which depends on the virus control, in normal and long-term progressors. The nonprogressive infection of African nonhuman primate SIV hosts is characterized by partial mucosal CD4⁺ T-cell restoration, despite high viral replication. Complete, albeit very slow, recovery of mucosal CD4+ T-cells occurs in controllers. Early ART does not prevent acute mucosal CD4⁺ T-cell depletion, yet it greatly improves their restoration, sometimes to preinfection levels. Comparative studies of the different models of SIV infection support a critical role of immune activation/inflammation (IA/INFL), in addition to viral replication, in CD4⁺ T-cell depletion, with immune restoration occurring only when these parameters are kept at bay. CD4⁺ T-cell depletion is persistent, and the recovery is very slow, even when both the virus and IA/INFL are completely controlled. Nevertheless, partial mucosal CD4⁺ T-cell recovery is sufficient for a healthy life in natural hosts. Cell death and loss of CD4⁺ T-cell subsets critical for gut health contribute to mucosal inflammation and enteropathy, which weaken the mucosal barrier, leading to microbial translocation, a major driver of IA/INFL. In turn, IA/INFL trigger CD4⁺ T-cells to become either viral targets or apoptotic, fueling their loss. CD4⁺ T-cell depletion also drives opportunistic infections, cancers, and comorbidities. It is thus critical to preserve CD4⁺ T cells (through early ART) during HIV/SIV infection. Even in early-treated subjects, residual IA/INFL can persist, preventing/delaying CD4⁺ T-cell restoration. New therapeutic strategies limiting mucosal pathology, microbial translocation and IA/INFL, to improve CD4⁺ T-cell recovery and the overall HIV prognosis are needed, and SIV models are extensively used to this goal.

Strong mucosal immune responses in SIV infected macaques contribute to viral control and preserved CD4+ T-cell levels in blood and mucosal tissues

BACKGROUND

Since there is still no protective HIV vaccine available, better insights into immune mechanism of persons effectively controlling HIV replication in the absence of any therapy should contribute to improve further vaccine designs. However, little is known about the mucosal immune response of this small unique group of patients. Using the SIV-macaque-model for AIDS, we had the rare opportunity to analyze 14 SIV-infected rhesus macaques durably controlling viral replication (controllers). We investigated the virological and immunological profile of blood and three different mucosal tissues and compared their data to those of uninfected and animals progressing to AIDS-like disease (progressors).

RESULTS

Lymphocytes from blood, bronchoalveolar lavage (BAL), and duodenal and colonic biopsies were phenotypically characterized by polychromatic flow cytometry. In controllers, we observed higher levels of CD4+, CD4+CCR5+ and Gag-specific CD8+ T-cells as well as lower immune activation in blood and all mucosal sites compared to progressors. However, we could also demonstrate that immunological changes are distinct between these three mucosal sites.Intracellular cytokine staining demonstrated a significantly higher systemic and mucosal CD8+ Gag-specific cellular immune response in controllers than in progressors. Most remarkable was the polyfunctional cytokine profile of CD8+ lymphocytes in BAL of controllers, which significantly dominated over their blood response. The overall suppression of viral replication in the controllers was confirmed by almost no detectable viral RNA in blood and all mucosal tissues investigated.

CONCLUSION

A strong and complex virus-specific CD8+ T-cell response in blood and especially in mucosal tissue of SIV-infected macaques was associated with low immune activation and an efficient suppression of viral replication. This likely afforded a repopulation of CD4+ T-cells in different mucosal compartments to almost normal levels. We conclude, that a robust SIV-specific mucosal immune response seems to be essential for establishing and maintaining the controller status and consequently for long-term survival.

Selective transmission of R5 HIV-1 variants: where is the gatekeeper?

To enter target cells HIV-1 uses CD4 and a coreceptor. In vivo the coreceptor function is provided either by CCR5 (for R5) or CXCR4 (for X4 HIV-1). Although both R5 and X4 HIV-1 variants are present in body fluids (semen, blood, cervicovaginal and rectal secretions), R5 HIV-1 appears to transmit infection and dominates early stages of HIV disease. Moreover, recent sequence analysis of virus in acute infection shows that, in the majority of cases of transmission, infection is initiated by a single virus. Therefore, the existence of a "gatekeeper" that selects R5 over X4 HIV-1 and that operates among R5 HIV-1 variants has been suggested. In the present review we consider various routes of HIV-transmission and discuss potential gatekeeping mechanisms associated with each of these routes. Although many mechanisms have been identified none of them explains the almost perfect selection of R5 over X4 in HIV-1 transmission. We suggest that instead of one strong gatekeeper there are multiple functional gatekeepers and that their superimposition is sufficient to protect against X4 HIV-1 infection and potentially select among R5 HIV-1 variants. In conclusion, we propose that the principle of multiple barriers is more general and not restricted to protection against X4 HIV-1 but rather can be applied to other phenomena when one factor has a selective advantage over the other(s). In the case of gatekeepers for HIV-1 transmission, the task is to identify them and to decipher their molecular mechanisms. Knowledge of the gatekeepers' localization and function may enable us to enhance existing barriers against R5 transmission and to erect the new ones against all HIV-1 variants.

HIV-1-induced depletion of CD4+ T cells in the gut: mechanism and therapeutic implications

The mechanism of CD4+ T cell depletion remains a central unresolved issue in AIDS research. Recent studies have examined the massive depletion of CD4+ T cells observed in macaque models of acute HIV infection. A key question is whether the observed CD4+ T cell death is due to direct consequences of viral infection and to indirect mechanisms including increased expression of mediators of T-cell apoptosis. The therapeutic implications of the early CD4+ T cell loss are discussed.

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Human immunodeficiency virus type 1 gag-specific mucosal immunity after oral immunization with papillomavirus pseudoviruses encoding gag

Mucosal surfaces are the primary portals for human immunodeficiency virus (HIV) transmission. Because systemic immunization, in general, does not induce effective mucosal immune responses, a mucosal HIV vaccine is urgently needed. For this study, we developed papillomavirus pseudoviruses that express HIV-1 Gag. The pseudoviruses are synthetic, nonreplicating viruses, yet they can produce antigens for a long time in the immune system. Here we show that oral immunization of mice by the use of papillomavirus pseudoviruses encoding Gag generated mucosal and systemic Gag-specific cytotoxic T lymphocytes that effectively lysed Gag-expressing target cells. Furthermore, the pseudoviruses generated Gag-specific gamma interferon-producing T cells and serum immunoglobulin G (IgG) and mucosal IgA. In contrast, oral immunization with plasmid DNA encoding HIV-1 Gag did not induce specific immune responses. Importantly, oral immunization with the pseudoviruses induced Gag-specific memory cytotoxic T lymphocytes and protected mice against a rectal mucosal challenge with a recombinant vaccinia virus expressing HIV-1 Gag. Thus, papillomavirus pseudoviruses encoding Gag are a promising mucosal vaccine against AIDS.

Systemic and intestinal immune responses to HIV-2287 infection in Macaca nemestrina

Nonhuman primate models of human AIDS have been used successfully to evaluate candidate vaccines and infection intervention therapies. Successes of pathogenicity studies in primate models have been limited because of the varied infection outcomes and characteristic low number of study animals. The acutely pathogenic HIV-2(287)--Macaca nemestrina model has shown promise both in antiviral drug evaluation and in pathogenicity studies. Here we describe virus replication, spread, and host responses during the first 28 days of HIV-2(287) infection. Focusing on 18 macaques from a larger 27-macaque study, we report changing virus loads, CD4(+) cell depletions, and antibody responses both systemically and in the mucosa of the small intestine. After intravenous inoculation, blood and intestinal tissue were collected from pairs of macaques at 12 hr and 1, 2, 4, 6, 10, 14, 21, and 28 days postinfection. Specimens were examined for evidence of infection by quantitative cultures, in situ hybridization, lymphocyte subset monitoring, and antibody production. The data were presented serially as though all samples were collected from a single macaque. The highest blood virus loads were detected between days 10 and 14 and subsequently decreased through day 28. This coincided with a significant increase in ileum mucosa virus loads on day 10, which became undetectable by day 28. The lowest levels of CD4(+) cells were observed on days 21 and 28 in blood and ileum mucosa. CD4(+):CD8(+) cell ratios in blood and ileum dropped dramatically after day 10 to lowest levels by day 28. Intestinal virus loads were inversely correlated with CD4(+) cell and virus-specific antibody levels in the ileum after day 6. These results underscore the suitability of this model for pathogenicity studies as well as the importance of the intestinal lymphoid tissues as an initial site of virus replication and cell destruction during the acute, asymptomatic stage of AIDS development.

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

GASTROENTROLOGY 2001;120:607-621

Fat malabsorption assessed by 14C-triolein breath test in HIV-positive patients in different stages of infection: is it an early event?

The aim of this study was to evaluate fat absorption in HIV-positive (HIV+) patients in different phases of HIV infection using a 14C-triolein breath test. We distributed 47 HIV+ patients according to the 1993 Centers for Disease Control Revised Classification: 20 in Group 2 (A1 or A2) and 27 in Group 3 (B1, B2, A3, B3, or C). Ten HIV-negative healthy subjects comprised the control group (Group 1). All individuals underwent a 14C-triolein breath test. Parasitic infection was evaluated through three stool exams, including Cryptosporidium and Isospora investigation. The median value of cumulative 6 hours' 14C excretion expressed as percentage of the 14C given as triolein was significantly higher in Group 1 (8.4%) than Group 2 (5.5%) or Group 3 (3.4%), p = 0.04 and p << 0.01, respectively. Fat malabsorption was found in 25% of Group 2 individuals, 52.6% of those without diarrhea in Group 3, and was correlated with CD4+ lymphocyte counts (p << 0.01). Fat malabsorption is a common feature in advanced stages of HIV infection, even in the absence of diarrhea and is also present in asymptomatic HIV+ patients. These findings suggest that malabsorption is an early event in HIV-infected individuals and is correlated with the degree of immunosuppression.

Pattern of mucosal adaptation in acute and chronic pouchitis

PURPOSE

Variant pathological changes have been observed in ileoanal pouches, including inflammation, villous atrophy, and crypt hyperplasia. Therefore, we investigated the type and degree of mucosal adaptation in patients with ulcerative colitis and familial adenomatous polyposis.

METHODS

Forty-two patients with ulcerative colitis and 14 patients with familial adenomatous polyposis with ileoanal pouches were assessed. Samples were taken from three months to eight years after creation of an ileoanal pouch. Mucosal architecture was examined by morphometry after microdissection.

RESULTS

Structural changes of the mucosa can be categorized into three groups. Compared with preoperative values, patients without pouchitis (73 percent) has only minor decrease of villous length (402 microm vs. 540 microm) and increase in crypt depth (274.5 microm vs. 177 microm). In patients with acute pouchitis (20 percent), a slight increase in villous length (477 microm vs. 402 microm) and pronounced crypt hyperplasia (376 microm vs. 274.5 microm) was observed compared with noninflamed ileoanal pouches. In contrast, in patients with chronic pouchitis (7 percent), severe villous atrophy (62.5 microm) and crypt hyperplasia (543 microm) was found.

CONCLUSIONS

Minor structural changes of ileoanal pouch mucosa develop early as an adaptive response to a new environment. Only in a small group of patients with chronic pouchitis does severe villous atrophy and crypt hyperplasia of the ileoanal pouch mucosa develop, most likely as a consequence of mucosal inflammation.

HIV/SIV enteropathy

Evidence is increasing that HIV/SIV-induced changes in the highly differentiated gut-associated immune system play a central role in the pathogenesis of gastrointestinal manifestations in HIV/SIV infection. It has been shown in both humans infected with HIV and in nonhuman primates infected with SIV that a rapid, very early, and more pronounced loss of CD4+ T-cells occurs in the mucosa in comparison to the peripheral blood. The loss of this important regulatory T-cell subset might explain mucosal immunodeficiency with the consequence of opportunistic mucosal infections. In addition, there is evidence that small intestinal damage occurs independently of secondary infections (HIV/SIV enteropathy). In late-stage human disease, HIV enteropathy is characterized by villous atrophy with hyporegeneration and dysmaturation of intestinal epithelial cells. In SIV infection of macaques, villous atrophy is a very early event; however, it is accompanied by crypt cell hyperproliferation. Early- and late-stage enteropathy in immunodeficiency virus infection may represent two types of immunologically mediated mucosal transformation in which the number and state of activation of regulatory T cells determine whether hypo- or hyperproliferative villous atrophy occurs.

HIV-1 gp120 accelerates Fas-mediated activation-induced human lamina propria T cell apoptosis

Intestinal mucosa represents an important portal of entry of HIV and a site of virus reservoir and active replication. Recently, in HIV patients, an early depletion of intestinal lamina propria T lymphocytes (LPT) has been described. HIV-1 gp120 has been demonstrated to promote apoptosis in noninfected isolated peripheral blood T cells, therefore we investigated whether gpl20 modulates apoptosis of normal human intestinal lamina propria T cells. Purified T cells were obtained by immunomagnetic negative selection from human lamina propria mononuclear cells isolated from surgical specimens by enzymatic procedure. Cells were incubated with or without recombinant gpl20 (10 microg/ml) and cultured either in the absence of any stimulus or in the presence of plate-bound anti-CD3 Ab (OKT3) or soluble anti-CD2 Ab (T11(2) + T11[3]). Apoptosis was assessed by flow cytometric analysis after propidium iodide staining. We demonstrated that preincubation of normal LPT cells with HIV-1 gpl20 accelerates the apoptosis observed during CD2-pathway stimulation of LPT cells. This process is mediated by Fas/Fas ligand interaction and related to an increased induction of Fas ligand mRNA by gpl20. Therefore HIV-1 gp120 could contribute to the depletion of noninfected LPT cells inducing a premature cell death.

The impact of HIV infection on lactose absorptive capacity

Forty HIV-infected adult patients at different disease stages and 44 healthy volunteers were evaluated for lactose malabsorption using the hydrogen breath test after 20 g lactose ingestion. All subjects were previously tested for breath hydrogen (H2) excretion after 12 g lactulose ingestion. The presence of intestinal superinfections, gastrointestinal symptoms and the intensity of clinical intolerance after lactose load were accurately searched in each patient. The cumulative H2 excretion after lactulose did not significantly differ between the different groups studied. The prevalence of lactose malabsorption turned out to be significantly higher (P < 0.001) in HIV-infected patients (70%) than in controls (34%). Moreover, in patients in more advanced disease stages the degree of lactose malabsorption was significantly greater than in patients at earlier disease stages, who did not differ from healthy volunteers. Furthermore the degree of lactose intolerance was significantly greater (P < 0.001) in symptomatic patients than in those without intestinal symptoms and in healthy volunteers, while no significant difference was observed between these latter groups. The results here demonstrate the negative impact of HIV infection on lactose absorptive capacity in adult patients, particularly marked in more advanced stages of the disease, suggesting that, in addition to the presence of the virus alone, other factors may contribute to determine the enterokinetic alterations responsible for lactase deficiency.

Pathophysiology of HIV-associated diarrhea

Considerable advances have been made in the evaluation and treatment of diarrhea in HIV-infected individuals, although gaps in knowledge still exist. The availability of newer and more powerful antiretroviral agents should allow a better definition of the effect of local HIV infection on intestinal function. Further attention to the pathophysiology of diarrhea should lead to improvements in diagnosis and treatment.

Advances in mucosal immunology

HIV infection is likely to remain a significant medical and scientific problem well into the twenty-first century. During the first 15 years of the epidemic, much has been learned about the biology of HIV infection, but the majority of biomedical research has focused on the peripheral circulation. It is likely that the behavior of the virus within the unique immunologic environment of the intestinal mucosa differs from that which is observed in the periphery. Many clinical and epidemiologic features of HIV infection offer compelling reasons to encourage further examination of the mucosal immune system's role in AIDS pathogenesis. This article has touched on most of the significant observations concerning the mucosal immune system and HIV infection, and it is clear that much remains to be done. As mentioned earlier, the mucosal abnormalities observed in HIV infection are likely to have many causes. Careful evaluation of patients with early disease and fewer confounding variables may provide fresh insight into AIDS pathogenesis. Similarly, prospective evaluation of selected patient populations may be more informative in characterizing the progressive alterations in mucosal immune function than random cross-sectional studies of poorly defined groups. It is equally important for immunologic assessment to be correlated with nutritional and symptomatic evaluation. Finally, the success or failure of future antiretroviral therapies will be critically related to the impact of such agents on lymphoid reservoirs of HIV infection such as the gastrointestinal tract, which are at present refractory to treatment.

Infectious Diarrhea

Infectious diarrhea constitutes a major source of morbidity and mortality for all age groups. The focus of this article is to identify high risk host and pathogenic risk determinants of enteric infections, discuss pathophysiologic mechanisms for diarrhea, review conventional and upcoming therapeutic managements of bacterial, protozoal or viral-type diarrhea, and describe the integral role of the pharmacist in the overall care of patients having this illness.

Duodenal intraepithelial and lamina propria T lymphocytes in human immunodeficiency virus-infected patients with and without diarrhoea

BACKGROUND

Diarrhoea is an important problem in human immunodeficiency virus (HIV)-infected patients. Intestinal pathologic conditions may arise from changes in local immunocyte populations. The aims of our study were to establish the histologic features of the duodenal mucosa of HIV-infected patients and to determine a) the phenotype of small-intestinal-intraepithelial (IELs) and lamina propria (LPLs)-lymphocytes; b) their degree of activation and differentiation within the lamina propria; and c) their relation to the presence of diarrhoea.

METHODS

Distal duodenal biopsy specimens were obtained prospectively from 29 HIV-infected patients-11 patients with diarrhoea (group 1) and 18 patients without diarrhoea (group 2)- and from 42 patients who had neither any risk factor for HIV nor diarrhoea (group 3). Histopathologic and immunohistochemical studies were combined with flow cytometric analysis, after separation of the mucosal intraepithelial compartment from the lamina propria.

RESULTS

The median number of IELs and the percentage of gamma delta IELs were both unchanged in HIV-infected patients as compared with controls. In HIV-infected patients LP CD4 cells were decreased, and LP CD8 cells increased. No significant difference was found in the expression of CD25 or CD27 within the LP CD8 populations of HIV-infected patients in groups 1 and 2.

CONCLUSIONS

These findings suggest that the occurrence of diarrhoea in HIV-infected patients is unrelated to IEL and LPL phenotype.

Experimental mucosal disease in cattle: changes in the number of lymphocytes and plasma cells in the mucosa of the small and large intestine

Changes in the number of lymphocyte and plasma cell subtypes were investigated in the lamina propria and in the epithelium of the small and large intestine of cattle with mucosal disease. Mucosal disease had been induced experimentally in seven out of 13 animals persistently viremic with non cytopathogenic BVD-virus by inoculation with a matching cytopathogenic BVD-virus. For comparison, six clinically healthy, persistently viremic cattle were used. IgA+, IgM+ and IgG1+ plasma cells, BoCD4+, BoCD8+ and gamma delta + T-lymphocytes, and the antigen of the cytopathogenic BVD-virus were demonstrated in tissue sections by immunohistochemistry. Distribution of cellular subtypes in the controls was consistent with data reported from non infected cattle. In cattle with mucosal disease, a decrease in the number of plasma cells which was significant for IgA+ and IgM+, but not for IgG1+ plasma cells was found in the lamina propria. The number of BoCD4+ T-lymphocytes was reduced in the small intestine, whereas their number per mm2 of mucosa was increased in the large intestine. Numbers of intraepithelial BoCD8+ and gamma delta + T-lymphocytes were severely decreased. Antigen of the cytopathogenic BVD-virus was detected predominantly in epithelial cells of the crypts. Overall there is a severe loss of effector cells which are essential components of the humoral and cell mediated immune protection of the mucosal barrier. The decrease of immunoregulatory cells in the lamina propria and epithelium may contribute to the transformation of mucosal architecture in mucosal disease.

Special features of the intestinal lymphocytic system

The gastrointestinal lymphocytic system can be divided in two functional compartments, the organized lymphoid tissue, for example, the Peyer's patches, and the lymphocytes located diffusely in the mucosa, the lamina propria lymphocytes (LPL), and the intra-epithelial lymphocytes (IEL). Antigens enter the Peyer's patches as the afferent part of the GALT via specialized epithelial cells called M cells. After the initiation of the immune response by antigen processing and presentation to B and T cells in Peyer's patches, primed lymphocytes leave the mucosa via the thoracic duct. Finally they migrate back to the mucosa where they exert effector functions. Adhesion molecules, including integrins, especially alpha 4 beta 7 and alpha E beta 7 (HML-1) are involved in these homing and adhesion processes. LPL and LEL differ from peripheral blood lymphocytes in their expression of adhesion molecules and other surface and activation markers. Additionally, they exhibit functional features different from those of other lymphocyte compartments. In the mucosal immune system, plasma cells mainly secrete IgA, which is part of the specialized humoral defence in the gut.

Increased numbers of granzyme-B-expressing cytotoxic T-lymphocytes in the small intestine of HIV-infected patients

The objective of this study was to determine whether granzyme B-expressing cells, which identify activated cytotoxic lymphocytes, are present in the small intestinal mucosa of human immunodeficiency virus (HIV)-infected patients with and without diarrhea. Therefore, duodenal biopsy specimens from 29 HIV-infected patients (11 with diarrhea and 18 without diarrhea) and 15 control patients were stained for the presence of granzyme B expressing cells. In HIV-infected patients, a significantly increased expression of granzyme B in the lamina propria was observed (p = 0.00001): In 22 of 29 patients, at least 5-10 cells per high-power field were counted. In contrast, in 13 of 15 control patients, granzyme B was not expressed or minimally so, and in two others a maximum of five granzyme-B-expressing cells could be detected per high-power field. No significant difference was found between the HIV-infected patients with and without diarrhea. Double staining revealed that the granzyme-B-expressing cells were mainly CD3 positive. These data show that activated cytotoxic T lymphocytes (CTLs) are present in the duodenal mucosa of HIV-infected patients. No relation between the number of CTLs and the presence of diarrhea was demonstrated. CTLs are known to be involved in the pathogenesis of HIV infection and in the production of tissue injury, but their functional role in intestinal HIV-related pathology has yet to be elucidated.

Intraepithelial gamma/delta T cells in duodenal mucosa are related to the immune state and survival time in AIDS

The proportion of T-cell receptor gamma/delta+ cells and the CD4/CD8 ratio relative to all CD3+ intraepithelial lymphocytes (IEL) were determined by immunofluorescence in duodenal mucosa of late-stage (mostly CDC IVC1/D) subjects (n = 21) infected with human immunodeficiency virus type 1 (HIV-1). The gamma/delta fraction (median, 14.2%; range, 1.7 to 59.8%) was increased (P < 0.03) compared with that in HIV- controls (n = 11; median 2.8%; range, 0.3 to 38%). Also, the number of gamma/delta+ IEL per mucosal unit was increased (P < 0.05) in the HIV+ subjects (median, 11.1/U) compared with the controls (3.2/U). Approximately 100% of the gamma/delta+ IEL were CD8-, and most expressed the Vdelta1vJdelta1-encoded epitope (median, 90.9%). The total number of CD3+ IEL tended to be lower than in the controls (67.4 versus 72.9/U). Both the epithelium and the lamina propria contained mainly CD8+ T cells, the median ratios of CD4+ T cells being 1 and 7.6%, respectively. This result accorded with the reduced CD4 cell number in blood (median, 18 X 10(6)/liter). The HIV+ subjects had increased serum levels of neopterin and beta2-microglobulin (both P < 0.0001), probably reflecting immunostimulation. Serum neopterin and beta2-microglobulin were inversely related to duodenal gamma/delta IEL, particularly in the premortal group (r = -0.97 and r = -0.58, respectively). The increased gamma/delta IEL might reflect enhanced intestinal protection in late-phase HIV infection. Short survival expectancy (<7 months) was associated not only with high levels of neopterin and beta2-microglobulin but also with a reduced number of duodenal gamma/delta+ cells (P < 0.03).

Loss of CD4 T lymphocytes in patients infected with human immunodeficiency virus type 1 is more pronounced in the duodenal mucosa than in the peripheral blood. Berlin Diarrhea/Wasting Syndrome Study Group

Although changes in T lymphocyte subset distribution in the peripheral blood of patients infected with human immunodeficiency virus (HIV) are well defined it is not known whether these changes reflect changes in lymphoid compartments clearly involved in HIV related disease like the intestinal mucosa. This study analysed lymphocytes isolated simultaneously from the peripheral blood and duodenal biopsy specimens by three colour flow cytometry in eight asymptomatic HIV infected patients, 26 AIDS patients, and 23 controls. The proportion of CD4, CD8, CD4-CD8-, or gamma delta T cells did not correlate between circulating and duodenal T cells. CD4 T cells were reduced in the peripheral blood (7.5% (25th-75th percentile, 2-16%) v 52% (41-63%), p < 0.0005) and even more reduced in the duodenum (1% (1-2%) v 36% (23-57%), p < 0.0005) of AIDS patients compared with controls. Patients with asymptomatic HIV infection had intermediate CD4 T cells in the peripheral blood (24% (22-35%); p < 0.002 v controls; p < 0.01 v AIDS) but like AIDS patients very low CD4 T cells in the duodenum (3% (1-6%); p < 0.002 v controls). The ratio of duodenal to circulating CD4+ T cells was significantly reduced to 0.2 (0-1) in AIDS patients (p < 0.001) and even to 0.1 (0.04-0.5) in asymptomatic HIV infected patients (p < 0.002) compared with 0.72 (0.44-0.95) in controls. These findings show an early and preferential loss of duodenal CD4 T cells in HIV infection. Immunological abnormalities in HIV infection are distinct between lymphoid compartments, and profound immunodeficiency may occur in the intestinal immune system although circulating T cells are largely preserved.

Isolation of human immunodeficiency virus type 1 (HIV-1) RNA from feces by a simple method and difference between HIV-1 subpopulations in feces and serum

A simple method for the isolation and subsequent detection of human immunodeficiency virus type 1 (HIV-1) RNA from feces is described. Viral RNA was isolated by the method developed by Boom et al. (R. Boom, C.J.A. Sol, M.M.M. Salimans, C.L. Jansen, P.M.E. Wertheim-van Dillen, and J. van der Noordaa, J. Clin. Microbiol. 28:495-503, 1990), which was adapted for feces. HIV-1 RNA was detected by reverse transcription (RT) followed by a nested PCR encompassing the V3 region. Reconstruction experiments revealed that the efficiencies of the extraction technique and the subsequent RT-PCR were not considerably affected by the varied composition of feces. The method was applied on fecal specimens from 18 HIV-1-infected individuals, among which were samples that had been stored for 9 years. It appeared that HIV-1 RNA was detectable in the feces of 12 persons (67%). Viral RNA was present in the feces of persons who fulfilled the criteria for CDC class II and CDC class III HIV infection as well as in patients who were diagnosed with AIDS (CDC class IV). Direct sequencing of amplimers obtained from paired fecal and serum specimens showed that differences in sequence heterogeneity existed. In one patient a remarkable difference in the HIV-1 sequences between isolates from feces and serum was observed. In conclusion, HIV-1 RNA is frequently present in the feces of HIV-1-infected individuals, and in some cases the HIV-1 subpopulation in feces differs from the HIV-1 subpopulation in serum.

Cell differentiation and proliferation in the gastrointestinal tract with respect to the local immune system

Human intestinal lamina propria T cells have a low expression of the CD45RA antigen and a high expression of the CD45RO antigen. This phenotype is characteristic for memory T cells. In addition, T cells in the effector compartment of the mucosa bear surface antigens that are very rarely found in other sites of the immune system. Intestinal T cells also express functional IL-2 receptors, and IL-2 receptor alpha-chain mRNA, and are able to synthesize high amounts of IL-2. However, other markers of memory T cells, as CD29, are not expressed in high density in the lamina propria, indicating that lamina propria T cells differ from "classical" memory T cells. This is supported by functional studies in nonhuman primates infected rectally with Chlamydia trachomatis that show that lamina propria T cells do not proliferate after stimulation with antigen but rather provide helper function for immunoglobulin synthesis. These findings indicate a specific state of differentiation of lamina propria T cells that is adapted to the specific requirements in the gut. In inflammatory bowel disease (IBD) and in celiac disease, an increase in the number of CD25-positive activated T cells is found in involved mucosa. It has been shown that mucosal T-cell activation induces epithelial cell damage and mucosal transformation. Thus, a T cell-mediated damage may contribute to the pathogenesis of IBD. HIV-infected patients have a decreased number of CD4-positive T cells in the intestinal lamina propria. The number of CD25-positive activated T cells is also significantly decreased in the intestine compared to controls. Correlating with the presence of HIV-infected mononuclear cells in the mucosa, mucosal atrophy with hyporegeneration and enterocyte dysmaturation is observed. HIV might thus cause impairment and depletion of activated regulatory T cells in the intestinal lamina propria, which could lead not only to a breakdown of the mucosal immune barrier, resulting in a variety of opportunistic infections, but also to malabsorption, due to mucosal atrophy or enterocyte dysfunction. These findings indicate a close relationship between mucosal T cells and enterocyte proliferation and maturation.

Is there IgA of gut mucosal origin in the serum of HIV1 infected patients?

This study was performed in 77 HIV1 seropositive adult patients to characterise the IgA hyperglobulinaemia seen in the serum during the course of HIV infection. It was shown that both IgA1 and IgA2 subclass concentrations were simultaneously increased but the IgA1 increase was predominant. Secretory IgA (SIgA) concentration was significantly increased and IgA activity to gliadin, bovine serum albumin, and casein could be detected and was correlated with SIgA concentration. In contrast, IgA activity to cytomegalovirus and to tetanus toxoid did not correlate with total IgA concentration. These data suggest the presence of IgA from gut mucosal origin in the serum of these patients. Hyper IgA was inversely correlated with the CD4+ cell number. The increase of all parameters studied varied according to the total IgA concentration in the serum but was also directly related to the stage of immune deficiency in patients with hyper IgA.

Mucosal macrophage subsets of the gut in HIV: decrease in antigen-presenting cell phenotype

The effect of HIV infection on intestinal lamina propria macrophage subsets was investigated in 41 patients at various stages of HIV infection (asymptomatic HIV infection, n = 17; AIDS, n = 24). Duodenal biopsies taken from HIV patients at endoscopy were snap frozen and cryostat sections cut for immunohistochemical staining. MoAbs CD68 (EBM11, pan-macrophage marker), RFD1 (antigen-presenting cells) and RFD7 (mature phagocytic macrophages) were used to identify cell subsets using indirect immunoperoxidase or alkaline phosphatase. Double immunofluorescence using MoAbs to HIV proteins (p24, p17 and gp120) and RFD1 were used to identify HIV-infected antigen-presenting cells. Double immunofluorescence was also used to identify macrophages that expressed both RFD1 and RFD7 ('suppressor' macrophages). Intensity of HLA-DR expression in lamina propria cells was investigated using a MoAb to HLA-DR directly conjugated to glucose oxidase. The results show that there was no difference in overall density of macrophages, but there was a significant decrease in dendritic cells (RFD1+) in all clinical stages of HIV. There was no difference in the density of RFD7+ macrophages, nor was there a difference intensity of HLA-DR expression in lamina propria cells. Only four HIV-infected cells were positively identified in the 41 patients. This result suggests that the antigen-presenting arm of mucosal immune defences may be seriously compromised in HIV infection, and represents a further insult to mucosal immunity already impaired as a result of loss of CD4+ T lymphocytes. This may contribute to development of opportunist infection in the gut.

Loss of mucosal CD4 lymphocytes is an early feature of HIV infection

T cell subsets in the gut mucosa are distinct populations and their imbalance in HIV has specific implications in infection. Alterations in T cell subsets in duodenal biopsies were investigated in 17 asymptomatic HIV patients, 24 AIDS patients and 10 controls with non-ulcer dyspepsia. Immunohistochemistry and immunofluorescence using MoAbs to CD3, CD4, CD8, CD68, CD45RA, CD45RO and gp120 were performed on frozen sections. In the lamina propria, there was a significant depletion of CD4+ cells at all stages of HIV, but the density of CD8 lamina propria cells was increased. Intraepithelial lymphocytes were decreased in AIDS patients. There was a significant correlation between cellular density and mucosal CD3+ lymphocytes, and between mucosal CD3+ and CD8+ lymphocytes. Although mucosal CD4,CD45RO+ 'memory' cells were decreased, CD8,CD45RO+ 'memory' cells were increased. Mucosal CD4+ lymphocyte depletion occurred early in HIV, and thus their role in mucosal protection against opportunistic infection should be revised. Mucosal CD8+ lymphocytes initially increased, but decreased when CD4 blood counts were depleted, perhaps contributing to loss of host protection against infection. Intraepithelial lymphocyte depletion may also contribute to opportunistic infection.

Inhibitory effect of natural interferon alpha on human immunodeficiency virus type 1 transmission from epithelial cells to lymphocytes in vitro

The in vitro effect of human natural interferon alpha (IFN-alpha) on cell contact-mediated human immunodeficiency virus type 1 (HIV-1) transmission from epithelial cells to lymphocytes was examined. This type of infection is most likely to occur when the mucosal linings of the reproductive or digestive organs serve as latent viral reservoirs and HIV-1 invades the host through the basolateral surface of polarized epithelia upon contact with intraepithelial lymphocytes. The cell-to-cell infection model consisted of target MOLT-4 T lymphocytes exposed for various time periods to chronically HIV-1-infected intestinal monolayers (I407/YH5) in the presence of log10 dilutions of IFN (range 10(5)-10(-2) IU/ml). Concurrent measurements of resulting productive infection from MOLT-4 revealed that complete inhibition of reverse transcriptase activity was prevented by doses starting from 1 IU, whereas the cessation of p24 production occurred at 1000 IU of IFN present at inoculation. The results indicate that IFN can efficiently prevent not only cell-free but also cell-mediated HIV-1 infection--an important means of viral spread in vivo pertinent to HIV-1 transmission resulting from mucosa-lymphocyte interaction.

Gastrointestinal symptoms in patients infected with human immunodeficiency virus: relevance of infective agents isolated from gastrointestinal tract

The correlation of gastrointestinal symptoms and infections in 186 consecutive patients with human immunodeficiency virus (HIV) infection undergoing diagnostic endoscopy (oesophagogastroduodenoscopy, n = 124; colonoscopy, n = 37; both, n = 25) was investigated. Biopsy and stool samples were examined for infective agents. Only weight loss (p = 0.003) and dysphagia (p = 0.027) were more common in patients at stage CDC IV compared with earlier stages. In three of 27 patients at stage II/III and in 93 of 159 patients at stage IV an infective agent was identified in stool or gastrointestinal biopsy specimen (p < 0.001). Cytomegalovirus (n = 35), Candida sp (n = 28), M avium complex (n = 10), and Cryptosporidium (eight) were the most frequent agents detected. At stage IV, diarrhoea was more frequent in infected compared with non-infected patients (p = 0.006); however, an infective agent was also found in 39 of 82 patients at stage IV without diarrhoea. The frequency of gastrointestinal symptoms was not consistently increased in patients harbouring specific infective agents compared with non-infected patients. Our findings indicate that the pathogenic relevance of a gastrointestinal infection in HIV infected patients has to be verified and indirectly support the existence of an HIV associated enteropathy.

Peptides in the gastrointestinal tract in human immunodeficiency virus infection. The GI/HIV Study Group of the University of Calgary

The presence of immunoreactivity to the neuronal phosphoprotein B-50 and the peptides bombesin, calcitonin gene-related peptide, galanin, neurotensin, neuropeptide Y, somatostatin, substance P, and vasoactive intestinal polypeptide was examined in biopsy specimens from the duodenum and rectum of human immunodeficiency virus (HIV)-seropositive and HIV-seronegative male homosexual patients. The distribution of B-50 and the peptides was correlated with HIV serology, number of CD4+ lymphocytes, and the presence of HIV in biopsy culture. There was a very low incidence of enteric pathogens in both groups of patients. It was found that HIV-seropositive patients had a greater incidence of abnormal patterns of immunoreactivity (reduced intensity and/or density of innervation) in enteric nerves and enteroendocrine cells than HIV-seronegative patients. A reduction of substance P immunoreactivity was significantly correlated with reduced CD4+ lymphocyte count and HIV status; a similar trend was also seen for somatostatin and vasoactive intestinal polypeptide. Using B-50 as a marker, it was found that both groups of patients had altered patterns of immunoreactivity in rectal nerves. The findings of this study suggest that some of the clinical symptoms associated with HIV infection may be caused by a specific HIV enteropathy that influences enteric nerve and/or enteroendocrine cell function by altering the density of peptide immunoreactivity.

Effects of zidovudine treatment on the small intestinal mucosa in patients infected with the human immunodeficiency virus

Zidovudine is associated with hematologic toxicity and may also impair the rapidly proliferating intestinal epithelium. However, patients with human immunodeficiency virus (HIV) infection receiving zidovudine gain body weight, indicating improved absorptive function. In the present study, 33 HIV-infected patients with gastrointestinal symptoms who were undergoing duodenoscopy and who had no detectable secondary intestinal pathogens were investigated; 12 of them received zidovudine. HIV antigen p24 was detected in duodenal biopsy specimens by immunohistology in 3 of 12 patients with zidovudine treatment and in 10 of 21 patients without zidovudine treatment. Morphometry of duodenal specimens showed reduced villus surface area (P less than 0.05) without crypt hyperplasia independent of zidovudine therapy and reduced numbers of crypt mitoses in patients with mucosal HIV infection (P less than 0.001) compared with controls. In the duodenal brush border, patients with mucosal HIV infection (P = 0.006) and patients without zidovudine treatment (P = 0.009) had absent lactase/beta-glucosidase activity more frequently than controls, and all HIV-infected patients (P less than 0.025) except zidovudine recipients had decreased alkaline phosphatase activity compared with controls. These findings show a hyporegenerative atrophy of the small intestine and enterocyte dysmaturation associated with mucosal HIV infection. Improved enterocyte maturation, indicated by increased brush border enzyme activity, may contribute to the clinical benefit of HIV-infected patients from zidovudine therapy.

Phenotype and function of lamina propria T lymphocytes

Lamina propria T cells have a low expression of the CD45RA antigen and a high expression of the CD45RO antigen. This phenotype is characteristic for memory T cells (table 2). In addition, T cells in the effector compartment of the mucosa bear surface antigens which are very rarely found in other sites of the immune system. Intestinal T cells also express functional IL-2 receptors and IL-2 receptor alpha chain mRNA, and are able to synthesize high amounts of IL-2. However, another marker of memory T cells, CD29, is not expressed in high density in the lamina propria indicating that lamina propria T cells differ from 'classical' memory T cells. This is supported by functional studies in nonhuman primates infected rectally with C. trachomatis which show that lamina propria T cells do not proliferate after stimulation with antigen but rather provide helper function for immunoglobulin synthesis (table 2). The intestinal lamina propria therefore contains highly specialized T cells which have a distinctive phenotype and are activated. Functionally these T cells can be characterized as differentiated effector lymphocytes which respond to triggering the antigen-specific T cell receptor by secreting helper factors for B cells. This concept is supported by recent studies showing that the pattern of lymphokines produced by lamina propria T cells and the responsiveness to certain lymphokines differ from those of other lymphocyte populations [25]. Lamina propria T cells thus represent a subset of memory T cells with a unique maturational state.