Five penton base proteins form individual capsomeres at the 12 vertices, where each capsomere supports a trimeric fiber protein of variable size projecting from the vertex of the capsid. The viral capsid is composed of 252 capsomeres ( capsa, box méros, portion), including 240 hexons and 12 pentons. The external protein shell of the virus is icosahedral ( eikosí, twenty hédra, seat), with 20 triangular faces, 30 edges, and 12 vertices, and this symmetry is made up in large parts by the major virus protein, hexon. HAdVs are nonenveloped viruses with a diameter of 70 to 100 nm. General Description, Structural Proteins, and Genomic Structure However, effective treatment of HAdV-related diseases in immunocompromised patients still poses great challenges. Progress in molecular detection methods has rendered the detection, typing, and monitoring of adenoviral infections readily applicable in the clinical routine, and the tools required for risk assessment and timely diagnosis of invasive infection are available. However, adenoviruses play a particularly important role in patients with strongly impaired immune responses, in whom viral disease is associated with high morbidity and mortality, and infections in this setting are an important focus of the present review. Although the clinical courses are usually mild and self-limiting, infections may cause local outbreaks with severe courses, occasionally leading to a lethal outcome even in immunocompetent individuals ( 22, – 26). HAdV infections are readily transmittable and, in some instances, highly contagious. HAdVs were initially isolated mainly from military recruits with acute febrile respiratory disease and were subsequently associated with a number of clinical manifestations, including gastroenteritis, hepatitis, keratoconjunctivitis, meningoencephalitis, cystitis, upper and lower respiratory tract infections, and myocarditis, but also with noninflammatory conditions, such as obesity ( 14, – 21). Hence, adenoviruses are highly versatile organisms with a broad spectrum of clinical roles and applications. Moreover, the ability of adenoviruses to infect many cell types facilitated their exploitation as vectors for gene delivery to generate new tools for innovative treatments of important diseases, such as cancer and cardiovascular disorders ( 9, – 13). Investigations of adenovirus biology have led to Nobel Prize-winning discoveries in mRNA splicing and to important progress in the understanding of antigen presentation to T cells ( 8). Despite a number of studies addressing the possible role of HAdVs in human malignant disease, their putative oncogenicity in humans has remained enigmatic ( 5, – 7). In addition to their well-established role as infectious agents, adenoviral genomes were also shown to contain potent oncogenes, and the ability of certain types of the virus to induce tumor growth has been demonstrated in different mammalian animal models ( 2, – 4). Since their first isolation from adenoid tissue over 60 years ago ( 1), human adenoviruses (HAdVs) ( adénos, gland) have provided continuous challenges in a variety of clinical settings.
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