Intestinal secretory IgA immune response against human immunodeficiency virus among infected patients with acute and chronic diarrhea

Alteration of Polymeric Immunoglobulin Receptor and Neonatal Fc Receptor Expression in the Gut Mucosa of Immunodeficiency Virus-Infected Rhesus Macaques

Polymeric immunoglobulin receptors (pIgR) and neonatal Fc receptors (FcRn) are crucial immunoglobulin (Ig) receptors for the transcytosis of immunoglobulins, that is IgA, IgM and IgG, the levels of which in mucosal secretions were altered in both HIV- and SIV-infected individuals. To gain an insight into the changes of pIgR and FcRn expression after immunodeficiency virus (SHIV/SIV) infection, real-time RT-PCR methods were established and the mRNA levels of pIgR and FcRn in normal and SHIV/SIV-infected rhesus macaques were quantitatively examined. It was found that the levels of pIgR mRNA were within a range of 10(7) copies per million copies of GAPDH mRNA in the gut mucosa of rhesus macaques, which were up to 55 times higher than that in the oral mucosa, the highest among the non-gut tissues examined. Levels of FcRn mRNA were generally lower than that of pIgR, and the levels of FcRn mRNA in the gut mucosa were also lower than that in most non-gut tissues examined. Notably, the levels of pIgR mRNA in the duodenal mucosa were positively correlated with that of IL-17A in normal rhesus macaques. Both pIgR and FcRn mRNA levels were significantly reduced in the duodenal mucosa during acute SHIV infection and in the jejunum and caecum during chronic SHIV/SIV infection. These data expanded our knowledge on the expression of pIgR and FcRn in the gastrointestinal tract of rhesus macaques and demonstrated altered expression of pIgR and FcRn in SHIV/SIV, and by extension HIV infections, which might have contributed to HIV/AIDS pathogenesis.

Trials and tribulations of an African-led research and capacity development programme: the case for EDCTP investments

We describe the initiation and establishment of The University of Zambia - University College London Medical School (UNZA-UCLMS) Research and Training Project, an entirely African scientist-led, south-north partnership. In its 16 year existence, the project, by successfully obtaining competitive grant funding, has transformed itself into one of Africa's most productive African-led R&D programmes with training and visible research outputs. The project serves as a role model and now networks R&D and training activities with six southern African (10 institutions) and six European countries. This project case study illustrates that deep commitment is essential for success and that the factors which facilitate success in R&D in Africa need to be evaluated. The long-term prospects for sustaining the UNZA-UCLMS Project appear bright and are dependent on several factors: the ability to retain trained African scientists; obtaining continued competitive or donor grant funding support; and serious investment by the African governments involved. The recent 255 million Euros EDCTP investment in sub-Saharan Africa through south-north partnerships is expected to enhance existing African-led R&D programmes. African governments and scientists must rise to the challenge.

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Targeting of 3'-azido 3'-deoxythymidine (AZT)-loaded poly(isohexylcyanoacrylate) nanospheres to the gastrointestinal mucosa and associated lymphoid tissues

PURPOSE

The aim of the studv was to evaluate the capacity of poly(isohexylcyanoacrylate) nanospheres to concentrate 3'-azido 3'-deoxythymidine (AZT) in the intestinal epithelium and associated immunocompetent cells, which are known to be one of the major reservoirs of the human immunodeficiency virus (HIV).

METHODS

The tissue concentration of 3H-radiolabeled AZT in the gastrointestinal (GI) tract was obtained 30 and 9() minutes after intragastric administration to rats at a dose of 0.25 mg AZT/100 g of body weight. The distribution along the intestine was determined. AZT concentrations in the lymph were obtained by lymphatic duct cannulation.

RESULTS

Unlike the solution. nanoparticles did concentrate AZT very cfficiently in the intestinal mucosa, as well as in the Peyer's patches, and could simultaneously control the release of free AZT. Concentration in Peyer's patches was 4 times higher for nanoparticles, compared with the control solution. The tissue concentration was 30-45 microM, which was much higher than the reported IC50 of AZT (0.06-1.36 microM) and was regularly distributed along the gastrointestinal tract.

CONCLUSIONS

Nanoparticles have been shown to be efficient in concentrating AZT in the intestinal epithelium and gut-associated lymphoid tissues, supporting the view that these particles may represent a promising carrier to treat specifically the GI reservoir of HIV.

HEp-2 cell-adherent Escherichia coli and intestinal secretory immune response to human immunodeficiency virus (HIV) in outpatients with HIV-associated diarrhea

HEp-2 cell-adherent Escherichia coli and the human immunodeficiency virus (HIV) itself have recently been incriminated as causes of chronic HIV-associated diarrhea. This study sought to determine the prevalence of these two agents among HIV-infected patients with diarrhea in an outpatient setting in the United States and to compare their prevalence to that of other commonly recognized enteropathogens known to be present in this population. HEp-2 cell-adherent E. coli was found in 20 of 83 (24.1%) patients with diarrhea. A diffuse pattern of adherence was the most common, found in 14 of 20 (70%) patients, followed by a localized adherence pattern (6 of 20; 30%). An intestinal secretory immune response against the p24 antigen of HIV was found in 9 of 34 (27.5%) patients with HIV-associated diarrhea. The following pathogens or products were also detected in lower frequencies: Cryptosporidium spp. (10.8%), Clostridium difficile toxin (8.8%), microsporidia (6%), Isospora belli (3.6%), Blastocystis hominis (2.4%), Giardia spp. (1.2%), Salmonella spp. (1.2%), and Mycobacterium spp. (1.2%). The role of HEp-2 cell-adherent E. coli and HIV enteric infections in patients with HIV-associated diarrhea deserves further study.

Abnormal predominance of IgG in HIV-specific antibodies produced by short-term cultured duodenal biopsy specimens from HIV-infected patients

The aim of our study was to analyze HIV-specific humoral immunity in the intestinal mucosa at different stages of HIV infection in comparison with serum and saliva. Duodenal biopsy specimens from 30 AIDS patients and 9 HIV-infected patients without AIDS were cultured for 48 hours. Culture supernatants, as well as simultaneously obtained serum and saliva samples, were adjusted to the same immunoglobulin concentrations and tested for HIV-specific IgG and IgA by Western blot. The HIV antigen pattern differed clearly between IgA and IgG but was similar for each isotype independent of its origin (i.e., serum, saliva, or biopsy specimen supernatants). Short-term cultured duodenal biopsy specimens from HIV-infected patients at all stages produced predominantly IgG, which was broadly reactive with HIV antigens. Lower titers of HIV-specific IgA, which recognized few antigens, were found, mostly the glycoprotein gp160. At later stages of the disease compared with earlier stages, the reaction pattern of mucosal IgA from saliva and biopsy supernatants was even more restricted; secretory component was frequently absent. The abnormal predominance of HIV-specific IgG over IgA in mucosal secretions may result from abnormal antibody production in the mucosa rather than from serum leakage. Mucosal inflammation induced by HIV-IgG immune complexes and insufficient immune exclusion by secretory IgA may not only lead to increased mucosal HIV replication but may also contribute to gastrointestinal disease in HIV-infected patients.

Direct effect of type 1 human immunodeficiency virus (HIV-1) on intestinal epithelial cell differentiation: relationship to HIV-1 enteropathy

Human immunodeficiency virus (HIV)-infected patients display severe impairments of gastrointestinal functions, including diarrhea and malabsorption, even in the absence of opportunistic infections. Since HIV-1 proteins and nucleic acids have been detected in several cell types of the intestinal mucosa, it has been postulated that HIV-1 itself could alter enterocytic functions. In the present study, we analyzed the effect of HIV-1 on the differentiation process of the epithelial intestinal cell clone HT-29-D4, which mimics the maturation of enterocytes along the crypt-villus axis of the small intestine. We found that HIV-1 infection impairs cellular differentiation (i) by affecting the barrier function of the epithelium, as evidenced by a decrease in the transepithelial electrical resistance, and (ii) by inhibiting the activity of one major glucose absorption function, i.e., sodium/glucose cotransport. At the morphological level, HIV-1 infection of HT-29-D4 cells was associated with the formation of lumina, which are representative of a defect in cellular organization. These morphofunctional perturbations induced by HIV-1 could be mimicked by nocodazole, a microtubule-disrupting agent. Correspondingly, HIV-1 exposure of HT-29-D4 cells evoked a massive disruption of microtubules, as revealed by alpha-tubulin indirect immunofluorescence staining. A similar effect was observed after incubation of the cells with either recombinant gp120 or a monoclonal antibody against galactosylceramide (GalCer), the intestinal receptor for HIV-1 gp120, suggesting that the effect of HIV-1 was mediated by the binding of gp120 to GalCer. Based on these data, we propose that HIV-1 may selectively alter enterocytic functions through a direct effect on the intracellular architecture of the cells. In contrast with previous theories for HIV-1 enteropathy, our data support the concept that HIV-1 may perturb intestinal functions without necessarily infecting intestinal epithelial cells.

Serum and Intestinal Antitoxin Antibody Responses after Immunization with the Whole-Cell/Recombinant B Subunit (WC/rBS) Oral Cholera Vaccine in North American and Mexican Volunteers

Background: Immune protection against cholera infection is probably mediated in part by locally produced, intestinal secretory IgA (sIgA) antibodies. We study the kinetics of intestinal (sIgA) and systemic (serum IgG) antitoxin antibody responses after immunization with whole-cell/recombinant B subunit oral cholera vaccine (WC/rBS) in U.S. travelers to Mexico and Mexican volunteers. Methods: Two doses of WC/rBS were administered 10 days apart to ten U.S. adults, newly arrived in Mexico, and 18 Mexican nationals. Serum IgG and intestinal secretory IgA (sIgA) antibodies to the B subunit of cholera toxin were measured from day 0 to day 21 by a direct enzyme-linked immunosorbent assay (ELISA). Results: Positive serum IgG responses to vaccination were detected in 80% of U.S. adults and in 59% of Mexican adults. All volunteers, regardless of nationality, developed a positive sIgA antibody response to WC/rBS. No differences were observed between U.S. and Mexican volunteers in the magnitude and kinetics of serum IgG responses. We recorded differences in the kinetics of sIgA antibody, with early and late peak sIgA antitoxin responses demonstrated in the Mexican and U.S. volunteer groups, respectively. Although the presence or absence of antitoxin sIgA antibodies prevaccination (sIgA titer > 1:4) did not interfere with the final postimmunization magnitude of the antibody responses (sIgA measurements days 14 and 21), the initial measurement curves showed differences (sIgA measurements days 0 and 3). Conclusions: The WC/rBS vaccine stimulated antitoxin antibody formation both in serum and locally in the intestine. The presence or absence of specific sIgA antibodies prevaccination did not seem to interfere with the magnitude of the antibody responses postvaccination (days 14, 21). The measurement of sIgA responses in fecal extracts appears to provide a simple and sensitive method to assess the intestinal immune response to orally administered vaccines.

Gastrointestinal immune responses in HIV infected subjects

The gut associated lymphoid tissue is responsible for specific responses to intestinal antigens. During HIV infection, mucosal immune deficiency may account for the gastrointestinal infections. In this review we describe the humoral and cellular mucosal immune responses in normal and HIV-infected subjects.

Decreased cervicovaginal production of both IgA1 and IgA2 subclasses in women with AIDS

Paired sera and cervicovaginal secretions from 35 HIV-1-infected women representing different CDC stages of HIV infection were evaluated for total IgA, IgA1 and IgA2, for IgA, IgA1 and IgA2 to gp160, and for albumin. Age-matched healthy women (n = 45) served as controls. The secretion rates of total IgA, IgA1 and IgA2 were evaluated by calculating their relative coefficients of excretion by reference to albumin. In HIV-infected women, total IgA1 and IgA2 in sera and in cervicovaginal secretions increased proportionately as early as stages II + III and more markedly at stage IV. By contrast, the secretion rates of total IgA IgA1 and IgA2 were markedly reduced in AIDS women, the IgA2 secretion rate decreasing significantly as early as stages II + III. This apparent discrepancy was probably the result of increased transudation of serum-borne immunoglobulins into the vaginal cavity, since albumin levels in cervicovaginal secretions increased significantly according to the stages of disease. HIV-reactive IgA antibodies in serum, as in cervicovaginal secretions, were principally found within the IgA1 subclass. In women at stage IV, a high local production of IgA1 to gp160 occurred in spite of the impairment of cervicovaginal IgA synthesis, probably because of marked genital HIV replication at advanced stages.

Intracellular calcium release induced by human immunodeficiency virus type 1 (HIV-1) surface envelope glycoprotein in human intestinal epithelial cells: a putative mechanism for HIV-1 enteropathy

Intracellular Ca2+ ([Ca2+]i) was measured in single human epithelial intestinal HT-29-D4 cells with the Ca2+ probe Fura-2 and digital imaging microscopy. Treatment of these cells with HIV-1 surface envelope glycoprotein gp120 (or a soluble form of its precursor gp160) induced an important increase of [Ca2+]i. This effect was abolished by preincubation of the viral glycoprotein with neutralizing antibodies specific for the V3 domain of gp120. These antibodies inhibited the binding of both gp120 and gp160 to galactosylceramide (GalCer), the alternative HIV-1 receptor in HT-29-D4 cells. Moreover, treatment of HT-29-D4 cells with an anti-GalCer mAb induced an increase in [Ca2+]i and rendered the cells insensitive to HIV-1 glycoprotein stimulation. The calcium response resulted from release of Ca2+ from caffeine-sensitive intracellular stores. Finally, the viral glycoprotein specifically abrogated the calcium response to the neuropeptide agonist neurotensin, a stimulator of chloride secretion via inositol trisphosphate-mediated calcium mobilization. Reciprocally, after neurotensin stimulation, the cells did not respond to gp120, showing that neurotensin and gp120 stimulate a common pathway of [Ca2+]i mobilization. These results suggest that HIV-1 may directly alter ion secretion in the intestine and thus be the causative agent of the watery diarrhea associated with HIV-1 infection.

Methods for detection of an intestinal secretory immunoglobulin A response to Candida spp. and their preliminary application in human immunodeficiency virus-infected patients with chronic diarrhea

Six of 11 human immunodeficiency virus (HIV)-infected patients with chronic diarrhea, shedding only Candida spp. in their stools, elicited a Candida-specific secretory immunoglobulin A response. Similar responses were identified in only 1 of 10 HIV-positive patients with chronic diarrhea but without Candida spp. and in none of 10 HIV-negative subjects without diarrhea. Candida spp. may play a role in the etiology of chronic diarrhea associated with HIV infection.