Jawetz Chapter 32: Adenoviruses PDF

32 C H A P T E R Adenoviruses...

32 C H A P T E R Adenoviruses Adenoviruses can replicate and produce disease in the respi- type-specific epitopes on both the hexon and fiber polypep- ratory, gastrointestinal, and urinary tracts and in the eye. tides. All human adenoviruses display this common hexon Many adenovirus infections are subclinical, and virus may antigenicity. Pentons occur at the 12 vertices of the capsid and persist in the host for months. About one-third of the 57 have fibers protruding from them. The penton base carries known human serotypes are responsible for the most cases a toxin-like activity that causes rapid appearance of cyto- of human adenovirus disease. A few types serve as models pathic effects and detachment of cells from the surface on for cancer induction in animals. Adenoviruses are valuable which they are growing. Another group-reactive antigen is systems for molecular and biochemical studies of eukaryotic exhibited by the penton base. The fibers contain type-specific cell processes. They are also useful vectors for gene therapy antigens that are important in serotyping. Fibers are associ- approaches. ated with hemagglutinating activity. Because the hemagglu- tinin is type specific, hemagglutination-inhibition tests are commonly used for typing isolates. It is possible, however, to PROPERTIES OF ADENOVIRUSES recover isolates that are recombinants and give discordant reactions in antibody neutralization and hemagglutination- Important properties of adenoviruses are listed in Table 32-1. inhibition assays. Structure and Composition Classification Adenoviruses are 70–90 nm in diameter and display icosa- Adenoviruses have been recovered from a wide variety of hedral symmetry, with capsids composed of 252 capsomeres. species and grouped into five genera. All of the human ade- There is no envelope. Adenoviruses are unique among ico- noviruses are classified in the Mastadenovirus genus. At least sahedral viruses in that they have a structure called a “fiber” 57 distinct antigenic types have been isolated from humans projecting from each of the 12 vertices, or penton bases and many other types from various animals. (Figures 32-1 and 32-2). The rest of the capsid is composed Human adenoviruses are divided into seven groups of 240 hexon capsomeres. The hexons, pentons, and fibers (A–G) on the basis of their genetic, physical, chemical, and constitute the major adenovirus antigens important in viral biologic properties (Table 32-2). Adenoviruses of a given classification. group have fibers of a characteristic length, display consid- The DNA genome (26–45 kbp) is linear and double erable DNA homology encoding structural proteins (>85%, stranded. The GC content of the DNA is lowest (48–49%) compared with