![]() ![]() EBV infection downregulates expression of CD35. Human CD35, also known as complement receptor 1 (CR1), is an additional attachment factor for gp350/220, and can provide a route for entry of EBV into CD21-negative cells, including immature B-cells. This triggers fusion of the viral envelope with the cell membrane, allowing EBV to enter the B cell. Then, viral glycoprotein gp42 interacts with cellular MHC class II molecules. To enter B cells, viral glycoprotein gp350 binds to cellular receptor CD21 (also known as CR2). The mechanisms for entering these two cells are different. Replication cycle The EBV replication cycle Entry to the cell ĮBV can infect both B cells and epithelial cells. Viruses lacking the gp42 portion are able to bind to human B cells, but unable to infect. As a consequence, EBV made from B cells are more infectious to epithelial cells, and EBV made from epithelial cells are more infectious to B cells. In contrast, EBV from epithelial cells are rich in the three-part complexes because these cells do not normally contain HLA class II molecules. EBV that are made in the B cells have low numbers of gHgLgp42 complexes, because these three-part complexes interact with Human-leukocyte-antigen class II molecules present in B cells in the endoplasmic reticulum and are degraded. The viral three-part glycoprotein complexes of gHgL gp42 mediate B cell membrane fusion although the two-part complexes of gHgL mediate epithelial cell membrane fusion. EBV can infect different cell types, including B cells and epithelial cells. The term viral tropism refers to which cell types that EBV infects. This "first complete atomic model the icosahedral capsid, the capsid-associated tegument complex (CATC) and the dodecameric portal-the viral genome translocation apparatus." In July 2020, a team of researchers reported the first complete atomic model of the nucleocapsid of the virus. The DNA is surrounded by a protein nucleocapsid, which is surrounded by a tegument made of protein, which in turn is surrounded by an envelope containing both lipids and surface projections of glycoproteins, which are essential to infection of the host cell. The virus is about 122–180 nm in diameter and is composed of a double helix of deoxyribonucleic acid (DNA) which contains about 172,000 base pairs encoding 85 genes. Virology Simplified diagram of the structure of EBV Structure and genome Once EBV's initial lytic infection is brought under control, EBV latency persists in the individual's memory B cells for the rest of their life. ĮBV infects B cells of the immune system and epithelial cells. When infection with EBV occurs during adolescence or young adulthood, it causes infectious mononucleosis 35 to 50% of the time. In the United States and other developed countries, many people are not infected with EBV in their childhood years. Many children become infected with EBV, and these infections usually cause no symptoms or are indistinguishable from the other mild, brief illnesses of childhood. Infants become susceptible to EBV as soon as maternal antibody protection disappears. In the United States, about half of all five-year-old children and about 90% of adults have evidence of previous infection. Most people become infected with EBV and gain adaptive immunity. Infection with EBV occurs by the oral transfer of saliva and genital secretions. In 2022, a large study (population of 10 million over 20 years) suggested EBV as the leading cause of multiple sclerosis, with a recent EBV infection causing a 32-fold increase in the risk of developing multiple sclerosis. About 200,000 cancer cases globally per year are thought to be attributable to EBV. The virus is also associated with the childhood disorders of Alice in Wonderland syndrome and acute cerebellar ataxia and, by some evidence, higher risks of developing certain autoimmune diseases, especially dermatomyositis, systemic lupus erythematosus, rheumatoid arthritis, and Sjögren's syndrome. It is also associated with various non-malignant, premalignant, and malignant Epstein–Barr virus-associated lymphoproliferative diseases such as Burkitt lymphoma, hemophagocytic lymphohistiocytosis, and Hodgkin's lymphoma non-lymphoid malignancies such as gastric cancer and nasopharyngeal carcinoma and conditions associated with human immunodeficiency virus such as hairy leukoplakia and central nervous system lymphomas. The virus causes infectious mononucleosis ("mono" or "glandular fever"). The Epstein–Barr virus ( EBV), formally called Human gammaherpesvirus 4, is one of the nine known human herpesvirus types in the herpes family, and is one of the most common viruses in humans. ![]()
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