Human Herpes Virus Type 8 (HHV-8)

Human herpesvirus 8 (HHV-8), also known as Kaposi''s sarcoma-associated herpesvirus (KSHV), is a gammaherpesvirus primarily associated with Kaposi''s sarcoma (KS), primary effusion lymphoma (PEL), and multicentric Castleman''s disease (MCD). HHV-8 is transmitted through multiple routes, including saliva, sexual contact, blood transfusion, and organ transplantation. In endemic regions (such as sub-Saharan Africa), horizontal transmission through saliva during childhood is common; in non-endemic regions (such as North America), sexual transmission among men who have sex with men (MSM) predominates. The virus remains latent in endothelial cells and B lymphocytes, evading immune surveillance. Reactivation of latent virus is often triggered by immunosuppression (such as in HIV/AIDS or post-transplantation therapy), leading to lytic viral replication and the release of viral oncoproteins (such as vFLIP and vCyclin) and cytokines, which promote angiogenesis and tumor formation. HHV-8''s pathogenic mechanism involves hijacking host signaling pathways (such as NF-κB and PI3K/AKT) to inhibit apoptosis and enhance cell proliferation, ultimately leading to KS lesions characterized by spindle-shaped tumor cells and abnormal vascularity.

HHV-8 has a typical herpesvirus structure, consisting of an icosahedral capsid (approximately 125 nanometers in diameter) surrounded by a membrane layer and a lipid envelope. The envelope is studded with glycoproteins (such as gB, gH/gL), which are essential for host cell entry. The viral genome is a double-stranded DNA molecule of approximately 165 kilobases (kb) encoding over 90 open reading frames (ORFs). The genome is divided into unique regions (LURs and SURs) and terminal repeat regions (TRs), the latter of which facilitate circularization during latency. The HHV-8 genome contains conserved herpesvirus genes (e.g., DNA polymerase, capsid protein) and unique oncogenes, such as latency-associated nuclear antigen (LANA), viral G protein-coupled receptor (vGPCR), and viral interleukin-6 (vIL-6). LANA maintains the viral episome within the host cell nucleus and disrupts tumor suppressor proteins (e.g., p53, Rb), while vGPCR and vIL-6 mimic host cytokines to induce angiogenesis and inflammation.