Spectrum of Kaposi's sarcoma-associated herpesvirus, or human herpesvirus 8, diseases

Abstract

Human herpesvirus 8 (HHV-8), also known as Kaposi's sarcoma-associated herpesvirus (KSHV), discovered in 1994, is a human rhadinovirus (gamma-2 herpesvirus). Unlike other human herpesviruses (herpes simplex virus, Epstein-Barr virus, varicella-zoster virus, cytomegalovirus, HHV-6, and HHV-7), it is not widespread in the general population and has many unique proteins. HHV-8 is strongly associated with all subtypes of Kaposi's sarcoma (KS), multicentric Castleman's disease, and a rare form of B-cell lymphoma, primary effusion lymphoma. In addition, HHV-8 DNA sequences have been found in association with other diseases, but the role of the virus in these diseases is largely unconfirmed and remains controversial. The seroprevalence of HHV-8, based on detection of latent and lytic proteins, is 2 to 5% in healthy donors except in certain geographic areas where the virus is endemic, 80 to 95% in classic KS patients, and 40 to 50% in HIV-1 patients without KS. This virus can be transmitted both sexually and through body fluids (e.g., saliva and blood). HHV-8 is a transforming virus, as evidenced by its presence in human malignancies, by the in vitro transforming properties of several of its viral genes, and by its ability to transform some primary cells in culture. It is not, however, sufficient for transformation, and other cofactors such as immunosuppressive cytokines are involved in the development of HHV-8-associated malignancies. In this article, we review the biology, molecular virology, epidemiology, transmission, detection methods, pathogenesis, and antiviral therapy of this newly discovered human herpesvirus.

FIG. 1.

Morphology of KSHV (HHV-8) virions produced in PEL cell line KS-1. Arrows indicate fully mature virions.

FIG. 2.

Structure of the KSHV (HHV-8) genome. The central portion of the genome is flanked by the terminal repeats, labeled TR. The KSHV genome contains close to 100 open reading frames. Many of these are conserved in most herpesviruses; these are present in the conserved blocks (white boxes) and are not indicated. Other open reading frames are unique to rhadinoviruses, gammaherpesviruses, or KSHV and are present in more divergent areas of the genome (indicated by gray boxes). ORFs that have homology with herpesvirus saimiri are assigned the corresponding numbers, and ORFs without recognizable homologues were numbered separately and given the prefix K (K1 to K15) (248). Adapted from references and with permission of the publishers.

FIG. 3.

Purified HHV-8 virions. Supernatant from PMA-butyrate-induced KS-1 cells was harvested and fractionated by sucrose gradient centrifugation. The micrograph shows a cluster of negatively stained, mature HHV-8 virions (arrows), having a nucleocapsid core, defined tegument region, and outer lipid envelope. Surface spikes are evident on some particles.

FIG. 4.

Detection of KSHV (HHV-8) DNA in various clinical samples from KS patients and infected cells. Genomic DNA was extracted with DNAzol reagent (Gibco-BRL, Gaithersburg, Md.), and 1 μg of total DNA was used in the PCR. For the detections of KSHV/HHV-8 expression, two primers were synthesized from the minor capsid region of the HHV-8 sequence. The sense primer was 5′-TCG AGC AGC TGT TGG TGT ACC ACA T, and the antisense primer was 5′-TCC GTG TTG TCT ACG TCC AG. These primers, used in the PCR, were designed to amplify 142 bp of HHV-8. Each PCR cycle consisted of denaturation at 94°C for 1 min, primer annealing at 60°C for 45 s, and extension at 72°C for 2 min. The samples were amplified for 30 cycles. A positive reaction for PCR of HHV-8 showed amplified product of 142 bp. Molecular weight markers (marker VI) were from Boehringer Mannheim, Indianapolis, Ind. (A) PBMCs from classic KS patients and HIV-infected KS patients, KS lesions, and skin from HIV-infected KS patients. (B) HHV-8-infected cells: PBMCs, monocytes, primary monkey peripheral blood cells, PBMCs from KS patients, the KS-1 cell line, which is persistently infected with HHV-8, and KS lesions from two patients. (C) HHV-8 DNA detected in plasma of two Israeli patients from Ethiopia.

FIG. 5.

KS, PEL, and MCD: morphology and immunohistochemistry for viral antigens and detection of latent and lytic antigens to KSHV by IFA, with human sera and monoclonal antibody. (A) KS lesions in the lower extremities typical of a sporadic case. (B) Hyperpigmented KS lesions in the upper arms. (C) Histological section stained with hematoxylin and eosin of a nodular tumor stage lesion of KS. Note the spindle cell proliferation and abundant vasculature. (D) KSHV LANA (ORF-73) expression in KS. Staining with a rat monoclonal antibody revealed LANA positivity (diaminobenzidine, brown) in the nuclei of many spindle cells in a KS lesion. Positivity was also identified in endothelial cells lining the larger vascular spaces that may represent lymphatic vessels. (E) Histology of multicentric Castleman's disease. Hematoxylin- and eosin-stained section of a lymph node with HIV-associated Castleman's disease showing a single follicle with a large, concentrically arranged mantle zone surrounding a germinal center. The interfollicular area contains a network of small vessels. (F) KSHV vIL-6 expression in MCD. Immunohistochemical staining with polyclonal antiserum to vIL-6, showing cells with cytoplasmic positivity (diaminobenzidine, brown) in the mantle zone surrounding an atrophic germinal center. (G) Wright-Giemsa stain air-dried cytocentrifuge preparation of a KSHV-positive primary effusion lymphoma. The two tumor cells in this image are considerably larger than normal benign lymphocytes and neutrophils. The cells display significant polymorphism and possess moderately abundant basophilic cytoplasm. A prominent, clear perinuclear Golgi zone can be appreciated in the largest cell. The nuclei vary from large and round to highly irregular, multilobated, and pleomorphic and often contain one or more prominent nucleoli. (H) KSHV LANA (ORF-73) expression in KSHV-positive lymphomas. Staining with a rat monoclonal antibody revealed LANA positivity (alkaline phosphatase, red) in the nuclei of large, atypical lymphoma cells seen infiltrating reactive lymphoid tissue. This section was double stained with a polyclonal antiserum to kappa light chains (diaminobenzidine, brown), showing cytoplasmic positivity in a few of the surrounding cells but not the tumor cells. (I) KSHV vIL-6 expression in PELs. Immunohistochemical staining of cell block containing the BC-3 cell line was performed with a polyclonal rabbit antiserum to a vIL-6-specific peptide. Abundant expression is seen (diaminobenzidine, brown) in numerous lymphoma cells. (J) Detection by IFA of KSHV latent IgG antibody in serum from a classic KS patient. Typical nuclear speckles in the PEL cell line KS-1 are evident at a 1:50 dilution of the serum. (K) Presence of LANA-2 protein in KSHV-infected BCBL-1 cells. Diffuse finely speckled nuclear pattern of LANA-2 (green) is observed by IFA with LANA-2 monoclonal antibody. (L) Detection by IFA of KSHV lytic antibody in serum from a classic KS patient, using induced KS-1 cells. Apple green diffusely stained cells carry lytic antigen. Original magnifications: ×200 (D, E, F, and I), ×600 (C and H), and ×1,000 (G). Panels C to I copyright Amy Chadburn (Weill Medical College of Cornell University, New York, N.Y.). Panel K reproduced from reference with permission.