Faculty Bibliography

In this article, we discuss how human immunodeficiency virus (HIV) infection of activated CD4+ cells, expressing the chemokine receptors CCR5 or CXCR4, results in severe immunosuppression while evading the immune response. We describe how infection through mucosal surfaces or via the parenteral route results in rapid spread of the virus throughout the body prior to a vigorous CD8+ cytolytic T cell response, resulting in establishment of a viral set point. Data is examined that suggests the half-life of HIV virions in circulation is less than 6 hours and possibly as short as 30 minutes, whereas that of infected CD4 T cells is on average 1 to 1.5 days. We also explain how the rate of viral replication dictates the rate at which HIV evades the immune response and the rapidity with which resistance to antiviral medications may develop. Lastly, we show how anatomic and cellular reservoirs of latent viral pools have made the long-term goal of complete virus eradication difficult despite enormous advances in our therapeutic armamentarium.

The gastrointestinal mucosa harbors the majority of the body's CD4(+) cells and appears to be uniquely susceptible to human immunodeficiency virus type 1 (HIV-1) infection. We undertook this study to examine the role of differences in chemokine receptor expression on infection of mucosal mononuclear cells (MMCs) and peripheral blood mononuclear cells (PBMCs) by R5- and X4-tropic HIV-1. We performed in vitro infections of MMCs and PBMCs with R5- and X4-tropic HIV-1, engineered to express murine CD24 on the infected cell's surface, allowing for quantification of HIV-infected cells and their phenotypic characterization. A greater percentage of MMCs than PBMCs are infected by both R5- and X4-tropic HIV-1. Significant differences exist in terms of chemokine receptor expression in the blood and gastrointestinal mucosa; mucosal cells are predominantly CCR5(+) CXCR4(+), while these cells make up less than 20% of the peripheral blood cells. It is this cell population that is most susceptible to infection with both R5- and X4-tropic HIV-1 in both compartments. Regardless of whether viral isolates were derived from the blood or mucosa of HIV-1-infected patients, HIV-1 p24 production was greater in MMCs than in PBMCs. Further, the chemokine receptor tropism of these patient-derived viral isolates did not differ between compartments. We conclude that, based on these findings, the gastrointestinal mucosa represents a favored target for HIV-1, in part due to its large population of CXCR4(+) CCR5(+) target cells and not to differences in the virus that it contains

OBJECTIVE: Highly active antiretroviral therapy (HAART) has significantly decreased the incidence of infectious diarrhea affecting HIV-infected patients. Still, diarrhea remains a common symptom in HIV. We sought to determine the incidence of fat malabsorption as a cause of diarrhea in HIV patients receiving non-HAART (nucleoside analog only) and HAART (protease inhibitor-containing) antiretroviral regimens. METHODS: From June, 1995, to April, 1999, 88 HlV-infected patients underwent evaluation for diarrhea, which included endoscopy. We examined the incidence of fat malabsorption with a 24-h stool collection for fecal fat in a cohort of these patients (N = 33). Patients were divided into two groups, those receiving protease inhibitor-containing HAART and those receiving less intensive, nucleoside analog-only, non-HAART regimens. RESULTS: Thirty of 33 patients (90.9%) had fat malabsorption. Twenty of 21 patients not receiving HAART (95.2%) had fat malabsorption with a mean of 34 +/- 38 g of stool fat and a mean stool weight of 797 +/- 454 g. Ten of 12 patients receiving HAART (83.3%) had fat malabsorption with a mean of 46 +/- 86 g of stool fat and a mean stool weight of 800 +/- 647 g. Stool weight correlated with the degree of fat malabsorption (R = 0.77). CONCLUSION: Fat malabsorption represents a commonly undiagnosed entity in HIV-infected patients with diarrhea, whether or not they are receiving HAART therapy. Fecal fat determination should be considered a routine part of the diagnostic workup of HIV-infected patients experiencing diarrhea

Mucosal tissue is the main portal of entry for HIV-1 infection and, in macaques, has been demonstrated to be a significant compartment for viral replication and CD4+ T lymphocyte depletion. Quantitating tissue viral burden in addition to plasma viral load provides insights into HIV-1 pathogenesis and an additional means to gauge antiretroviral response. The aim of this study was to develop reliable, reproducible, and sensitive assays to quantitate tissue viral burden of HIV-1 RNA and DNA using 1-3 endoscopically acquired, rectosigmoid biopsies. Total DNA and RNA were simultaneously extracted following homogenization from the same tissue samples. Quantitative polymerase chain reaction (PCR) assay in the HIV-1 LTR region was used to detect viral DNA and RT-PCR for viral RNA. It was determined that HIV-1 RNA and DNA can be reproducibly quantified from a single rectosigmoid biopsy with minimal intra-assay or intra-patient variability. These results reflect high recovery of extracted nucleic acids with calculated results accurately reflecting in vivo levels. The techniques outlined differ from currently available approaches by incorporating control standards to identify loss or degradation of RNA and DNA from acquisition through the in vitro assay and permit extraction with high yields of RNA and DNA from the same tissue sample

The gastrointestinal mucosa is a major lymphoid tissue reservoir for human immunodeficiency virus (HIV) replication. Genotypic and phenotypic resistance patterns of HIV type 1 (HIV-1) RNA isolated from colonic mucosa were compared with those from the plasma and peripheral blood mononuclear cells (PBMC) of 7 patients. Genotyping was performed using full-sequence analysis, and phenotyping was performed using a recombinant virus assay. Mutations in the reverse-transcriptase (kappa=.84) and protease (kappa=.73) genes were highly concordant among compartments. Similarly, phenotypic resistance patterns were highly concordant among compartments (intraclass correlation coefficient,.91). In 5 instances among 3 patients, a different genotypic result was observed between plasma and the other tissue compartments. Mixtures of wild-type and mutated HIV-1 RNA were present in the mucosa and PBMC but not in the plasma. Despite significant concordance among compartments, mucosal- and PBMC-derived viral RNA showed instances of discordance with plasma-derived virus that may suggest compartmentalization of virus

The liver is a common site of pathology in HIV-infected patients. In patients with controlled HIV and minimal immunosuppression, infection with hepatitis viruses is common owing to the risk factors of sexual transmission or parenteral drug use. In patients with AIDS, the liver is a common site of lymphohematogenous dissemination of several infectious pathogens. A thorough diagnostic approach leads to a diagnosis of most hepatobiliary processes. The therapeutic nihilism that has surrounded hepatic disease, including viral hepatitis, is unwarranted, because treatment of the underlying HIV and the hepatic process may improve the quality of life and longevity of these patients

OBJECTIVE: To examine compartmental differences in co-receptor expression on CD4 lymphocytes between blood and gut using endoscopic biopsies. DESIGN: Mucosal and peripheral CD4 T cells from healthy controls were compared for co-receptor expression and vulnerability to infection by HIV-1. METHODS: Expression of CCR5 and CXCR4 was quantified by flow cytometry on isolated mucosal CD4 lymphocytes obtained from endoscopic biopsies and blood from healthy controls. Vulnerability to in vitro infection by both R5 and X4 strains was assessed by measuring p24. RESULTS: Biopsies yielded sufficient lymphocytes for flow cytometric characterization and infectivity studies. The percentage of mucosal CD4 T lymphocytes that expressed CCR5 and the per cell expression of CCR5 were both significantly increased compared with that in peripheral blood CD4 T lymphocytes. CXCR4 was expressed on the majority of CD4 lymphocytes in both compartments. In vitro infection of mucosal mononuclear cells supported greater viral replication of both R5 and X4 strains than peripheral blood mononuclear cells. CONCLUSIONS: Enhanced expression of CXCR4 and CCR5 on CD4 lymphocytes in normal intestinal mucosa predicts increased vulnerability to infection by both R5 and X4 HIV-1. Endoscopic biopsies provide a useful mucosal tissue sampling technique to identify compartmental immunologic differences that may be exploited by HIV-1 in establishing initial mucosal infection