The role of the oral environment in HIV-1 transmission

Human epithelial beta-defensins 2 and 3 inhibit HIV-1 replication

OBJECTIVE

Mechanisms underlying mucosal transmission of HIV-1 are incompletely understood. We describe the anti-HIV-1 activity of human beta-defensins (hBD), small cationic molecules that provide protection at mucosal surfaces.

METHODS AND RESULTS

HIV-1 induced expression of hBD-2 and -3 mRNA (but not that of hBD-1) 4- to 78-fold, respectively, above baseline in normal human oral epithelial cells. HIV-1 failed to infect these cells, even after 5 days of exposure. Recombinant hBD-1 had no antiviral activity, while rhBD-2 and rhBD-3 showed concentration-dependent inhibition of HIV-1 replication without cellular toxicity. Inhibition was greater against CXCR4-tropic than against the CCR5-tropic HIV-1 isolates. hBD-2 and hBD-3 induced an irreversible effect on virion infectivity, with electron microscopy confirming binding of hBDs to viral particles. Finally, hBD-2 and -3 induced downmodulation of the HIV-1 coreceptor CXCR4 (but not CCR5) in peripheral blood mononuclear cells and T lymphocytic cells as shown by confocal microscopy and flow cytometry.

CONCLUSIONS

This study shows for the first time that HIV-1 induces beta-defensin expression in human oral epithelial cells and that beta-defensins block HIV-1 replication via a direct interaction with virions and through modulation of the CXCR4 coreceptor. These properties may be exploited as strategies for mucosal protection against HIV-1 transmission.

Viral and host cofactors facilitate HIV-1 replication in macrophages

Human immunodeficiency virus type 1 (HIV-1) infection of CD4+ T lymphocytes leads to their progressive loss, whereas HIV-1-infected macrophages appear to resist HIV-1-mediated apoptotic death. The differential response of these two host-cell populations may be critical in the development of immunodeficiency and long-term persistence of the virus. Multiple contributing factors may favor the macrophage as a resilient host, not only supporting infection by HIV-1 but also promoting replication and persistence of this member of the lentivirus subfamily of primate retroviruses. An encounter between macrophages and R5 virus engages a signal cascade eventuating in transcriptional regulation of multiple genes including those associated with host defense, cell cycle, nuclear factor-kappaB regulation, and apoptosis. It is important that enhanced gene expression is transient, declining to near control levels, and during this quiescent state, the virus continues its life cycle unimpeded. However, when viral replication becomes prominent, an increase in host genes again occurs under the orchestration of viral gene products. This biphasic host response must fulfill the needs of the parasitic virus as viral replication activity occurs and leads to intracellular and cell surface-associated viral budding. Inroads into understanding how HIV-1 co-opts host factors to generate a permissive environment for viral replication and transmission to new viral hosts may provide opportunities for targeted interruption of this lethal process.

Envelope diversity, coreceptor usage and syncytium-inducing phenotype of HIV-1 variants in saliva and blood during primary infection

OBJECTIVE

To determine whether oral fluids can serve as a model for studying HIV-1 shedding, we compared the genetic diversity, coreceptor use, and syncytium-inducing (SI) phenotype of viral variants in saliva and blood during primary HIV-1 infection.

DESIGN

Observational cross-sectional cohort study.

METHODS

Blood plasma and saliva were sampled from 17 men early in primary HIV-1 infection. Viral diversity, predicted X4/R5 genotype and SI phenotype in samples were determined by heteroduplex tracking assays (HTAs) targeting the V1/V2 and V3 gp120 regions, sequence analyses and MT-2 cell assay.

RESULTS

Identical or very similar HTA banding and deduced amino acid sequence patterns in the V1/V2 and V3-encoding regions were observed between paired fluids of each subject. As assessed by V1/V2 HTA, 10 subjects had a single major viral variant and seven subjects exhibited multiple yet highly related variants. Two subjects had V1/V2 variants in blood that were identical to saliva but present in different relative abundances. A sexual transmission pair exhibited genetically dissimilar variants, suggesting transmission of a minor variant or rapid evolution during initial viremia. All subjects harbored R5 non-SI variants.

CONCLUSIONS

Relatively homogenous viral populations detected in plasma and saliva prior to seroconversion suggests that HIV-1 is disseminated to oral fluids early in infection and reflects the quasispecies in blood. These findings suggest that the oral cavity may serve as an easily accessible surrogate model for studying the dynamics of HIV-1 shedding at mucosal sites.

The diagnostic applications of saliva--a review

This review examines the diagnostic application of saliva for systemic diseases. As a diagnostic fluid, saliva offers distinctive advantages over serum because it can be collected non-invasively by individuals with modest training. Furthermore, saliva may provide a cost-effective approach for the screening of large populations. Gland-specific saliva can be used for diagnosis of pathology specific to one of the major salivary glands. Whole saliva, however, is most frequently used for diagnosis of systemic diseases, since it is readily collected and contains serum constituents. These constituents are derived from the local vasculature of the salivary glands and also reach the oral cavity via the flow of gingival fluid. Analysis of saliva may be useful for the diagnosis of hereditary disorders, autoimmune diseases, malignant and infectious diseases, and endocrine disorders, as well as in the assessment of therapeutic levels of drugs and the monitoring of illicit drug use.

Assessment of oral transmission using cell-free human immunodeficiency virus-1 in mice reconstituted with human peripheral blood leucocyte

Oral-genital contact is one of the risk factors for the transmission of human immunodeficiency virus (HIV) in adults. In recent reports, oral exposure to simian immunodeficiency virus (SIV) was found to have important implications for the achievement of mucosal transmission of HIV in a rhesus monkey animal model. In the present study, we aimed first to establish a small animal model which did not develop tonsils suitable for HIV oral mucosa transmission, using non-obese diabetic/severe combined immunodeficiency (NOD/SCID) mice and NOD/SCID B2m(null) mice grafted with human peripheral blood leucocytes (hu-PBL) and stimulated with interleukin (IL)-4, and second to investigate whether oral exposure to cell-free R5 and X4 HIV-1 could lead to oral transmission of HIV through intact or traumatized mucosal tissues in humanized mice. Both low and high concentrations of cell-free R5 and X4 viruses failed to cause oral transmission with or without trauma in hu-PBL-NOD/SCID and NOD/SCID Beta2m(null) mice, which presented a number of CD4+ cells in gingival tissues and oral cavities with or without tissue injury. The present results show that IL-4-administrated NOD/SCID B2m(null) mice are useful as a small-humanized model for the study of HIV oral infection, which may help to define the window of opportunity for oral transmission by the HIV virus in animal model experiments.

Human immunodeficiency virus type 1 infection and replication in normal human oral keratinocytes

Recent epidemiologic studies show increasing human immunodeficiency virus type 1 (HIV-1) transmission through oral-genital contact. This paper examines the possibility that normal human oral keratinocytes (NHOKs) might be directly infected by HIV or might convey infectious HIV virions to adjacent leukocytes. PCR analysis of proviral DNA constructs showed that NHOKs can be infected by CXCR4-tropic (NL4-3 and ELI) and dualtropic (89.6) strains of HIV-1 to generate a weak but productive infection. CCR5-tropic strain Ba-L sustained minimal viral replication. Antibody inhibition studies showed that infection by CXCR4-tropic viral strains is mediated by the galactosylceramide receptor and the CXCR4 chemokine coreceptor. Coculture studies showed that infectious HIV-1 virions can also be conveyed from NHOKs to activated peripheral blood lymphocytes, suggesting a potential role of oral epithelial cells in the transmission of HIV infection.

Characterization of human immunodeficiency virus type 1 in saliva and blood plasma by V3-specific heteroduplex tracking assay and genotype analyses

The gp120 V3-encoding region of human immunodeficiency virus type 1 (HIV-1) RNA derived from the saliva and blood plasma of 11 individuals was characterized by heteroduplex tracking assay and sequence analyses. R5-like viral variants were identified in both fluids of all subjects. X4-like variants were detected in the plasma and/or saliva of three subjects, indicating that X4-like variants are not excluded from the saliva compartment. Viral subpopulations were similar in both fluids of most subjects, suggesting that HIV-1 in oral fluids and blood may stem from a common source. These findings raise the possibility of using saliva as a noninvasive fluid for evaluating and monitoring viral evolution in infected persons.

Hyper-excretion of human immunodeficiency virus type 1 RNA in saliva

Anatomical compartments (e.g., the reproductive tract) are reservoirs of human immunodeficiency virus type-1 (HIV-1) and potential sites of residual infection in patients receiving anti-retroviral therapy (ART). Viral hyper-excretion relative to blood is a hallmark of reservoirs. To determine whether hyper-excretion can occur in the oral cavity, we compared viral loads in blood plasma and saliva of 67 adults. Salivary viral hyperexcretion was defined as a four-fold or higher viral load in saliva than in plasma. HIV-1 RNA was detected in 79% of plasma samples, in 44% of unfiltered saliva samples, in 16% of filtered saliva samples, and in 59% of saliva-derived cell pellets. Compared with non-hyper-excretors (n = 62), hyper-excretors (n = 5) had elevated levels of viral RNA in unfiltered saliva and saliva-derived cells, HIV-associated periodontal disease, gingival inflammation, and no combination ART. Morphological characterization of cell pellets identified lymphocytes as a likely HIV-1 source. These collective findings are consistent with an oral HIV-1 reservoir in selected individuals.

Positive and negative aspects of the human immunodeficiency virus protease: development of inhibitors versus its role in AIDS pathogenesis

In this review we summarize multiple aspects of the human immunodeficiency virus (HIV) protease from both structural and functional viewpoints. After an introductory overview, we provide an up-to-date status report on protease inhibitors (PI). This proceeds from a discussion of PI structural design, to how PI are optimally utilized in highly active antiretroviral triple therapy (one PI along with two reverse transcriptase inhibitors), the emergence of PI resistance, and the natural role of secretory leukocyte PI. Then we switch to another focus: the interaction of HIV protease with other genes in acute and persistent infection, which in turn may have an effect on AIDS pathogenesis. We conclude with a discussion on future directions in HIV treatment, involving multiple-target anti-HIV therapy, vaccine development, and novel reactivation-inhibitory reagents.

Identification of a novel secretory leukocyte protease inhibitor-binding protein involved in membrane phospholipid movement

Previous studies have suggested that human salivary secretory leukocyte protease inhibitor (SLPI) inhibits HIV-1 by binding to a host cell surface protein of unknown identity. Using the yeast two-hybrid assay, we identified a gene sequence encoding a novel SLPI-binding protein (SLPI-BP). The 1.5-kb cDNA encodes a 318-amino acid protein with a predicted transmembrane segment near the C-terminus. Sequence analysis revealed that SLPI-BP is the human scramblase protein that is involved in the movement of membrane phospholipids. Co-expression of SLPI and SLPI-BP followed by an S-protein pulldown assay confirmed the specific interaction between these two proteins. Our data represent the first report for the identity of SLPI-BP.

Visible and occult blood contamination of laryngeal mask airways and tracheal tubes used in adult anaesthesia

The purpose of this study was to compare visible and occult blood contamination of 50 laryngeal mask airways and 50 tracheal tubes following routine anaesthesia for procedures not involving the oropharyngeal or nasal cavities. All airway devices were examined visually for the presence of blood before washing in 100 ml of water. A semiquantitative dipstick was used to test for the presence of blood in the washings. Laryngeal mask airways were examined visually by both authors to test agreement. The results show that occult blood contamination occurred in 78% of tracheal tubes and 76% of laryngeal mask airways, while visible blood contamination was 16% and 12%, respectively. Other studies reporting visible blood contamination of airway devices probably underestimate the true incidence of blood contamination. Oral secretions following the use of these devices should be considered as high risk for transmission of blood-born viruses. Anaesthetic and recovery staff should be protected against the risks of occupational exposure to oral secretions following the use of airway devices.

Oral and systemic factors associated with increased levels of human immunodeficiency virus type 1 RNA in saliva

OBJECTIVE

The purpose of this investigation was to quantify human immunodeficiency virus type-1 (HIV-1) RNA in saliva and plasma and identify factors associated with increased salivary viral load.

STUDY DESIGN

Forty HIV-1-seropositive adults underwent oral examinations to assess mucosal and periodontal health. Whole saliva was evaluated for HIV-1 RNA titer and occult blood. Plasma viral load, CD4 cell count, HIV-1 staging, and antiretroviral therapy data were obtained from medical records. Associations between salivary titers and oral/systemic parameters were analyzed by means of t tests, Wilcoxon signed rank tests, Pearson's correlation coefficient, and analysis of covariance.

RESULTS

Forty-two percent of the subjects had detectable salivary HIV-1 RNA. Oral titers were highly correlated with plasma viral levels (r = 0.51, P <.01). HIV-associated periodontal disease (in particular, linear gingival erythema), severe gingival inflammation, and absence of antiretroviral therapy were associated with high salivary titers (P <.01).

CONCLUSIONS

Substantial quantities of HIV-1 can be shed in the oral cavity, particularly when inflammatory conditions are present. Salivary titer may be a useful indicator of systemic viral burden.

HIV topic update: oro-genital transmission of HIV

Several viruses, including the human immunodeficiency virus (HIV), can be found in blood and many body fluids including saliva, and are transmissible sexually across genital and particularly anal mucosae. A persisting concern has been the question of transmission of HIV by oral sexual practices. This review discusses the evidence for oro-genital transmission of HIV, detailing the presence and infectivity of HIV in genital fluids and saliva, the case reports and epidemiology of oro-genital HIV transmission, and the evidence from animal studies. Oral intercourse is not risk-free. The evidence suggests that the risk of HIV transmission from oro-genital sexual practices is substantially lower than that from penile-vaginal or penile-anal intercourse, that exposure to saliva presents a considerably lower risk than exposure to semen, and that oral trauma and ulcerative conditions might increase the risk of HIV transmission.

Endogenous salivary inhibitors of human immunodeficiency virus

The human immunodeficiency virus type 1 (HIV-1) is rarely transmitted through salivary secretions, due in part to the presence of endogenous inhibitors. Here, the protective characteristics of the intraoral environment are summarized and inhibitory factors that reduce HIV-1 infectivity in vitro described, focusing on secretory leucocyte protease inhibitor (SLPI), a 12-kDa mucosal protein that blocks HIV infection in several cell-culture systems. SLPI appears to interact with a cellular surface molecule to limit viral entry into target cells. To determine whether the inhibitor has a similar role in vivo, the contribution of salivary SLPI to anti-HIV-1 activity was assessed. Whole unstimulated filtered salivas from infected and uninfected donors contained similar concentrations of the inhibitor. Depletion from SLPI filtered saliva produced a corresponding loss of inhibitory activity. In general, filtered whole salivas obtained from 10 donors had antiviral activities that correlated positively with SLPI concentrations. However, some samples having SLPI well below the concentration required for inhibitory activity in vitro exhibited modest inhibition, suggesting the presence of other anti-HIV-1 components in oral fluids. Thus, SLPI is a major but not sole inhibitor of this virus in saliva.

Endogenous mucosal antiviral factors of the oral cavity

The oral cavity represents a unique site for mucosal transmission of human immunodeficiency virus type 1 (HIV-1). Unlike other mucosal sites, the oral cavity is rarely a site of HIV transmission despite detectable virus in saliva and oropharyngeal tissues of infected persons. One reason for this apparent paradox is the presence of endogenous mucosal antiviral factors. Innate inhibitory molecules, such as virus-specific antibodies, mucins, thrombospondin, and soluble proteins, have been identified and partially characterized from saliva. A recent addition to the growing list is secretory leukocyte protease inhibitor (SLPI), an approximately 12-kDa non-glycosylated protein found in serous secretions. Physiologic concentrations of SLPI potently protect adherent monocytes and activated peripheral blood mononuclear cells against HIV-1 infection. SLPI levels in saliva and semen but not breast milk approximate levels required for inhibition in vitro. Characterization of SLPI and other endogenous antiviral molecules may enhance our understanding of factors influencing mucosal HIV-1 transmission.