Principles of Virology, Volume 2. S. Jane Flint

Principles of Virology, Volume 2 - S. Jane Flint


Скачать книгу
contain a lysine at the carboxyl terminus, plasminogen cannot interact with NA and is not activated to plasmin. Therefore, HA is not cleaved. Data from Goto H, Kawaoka Y. 1998. Proc Natl Acad Sci U S A 95:10224–10228.

      A final emerging class of cellular macromolecules that can influence viral tropism are small, non-protein-encoding RNA species, called microRNAs. Although these RNAs do not result in new protein production, they can still dramatically affect host cell physiology. For example, microRNA-122 is conserved among vertebrates (but not present in invertebrates), and its expression is highest in the liver, where it likely contributes to fatty acid metabolism. The liver-tropic virus hepatitis C virus depends on microRNA-122 for reproduction. This microRNA binds directly to two adjacent sites close to the 5′ end of hepatitis C virus RNA, impacting RNA stability and genome replication (Volume 1, Chapter 9).

      Following reproduction at the site of entry, virus particles can remain localized or can spread to other tissues. Spread beyond the initial site of infection depends on multiple parameters, including the initial viral dose, the presence of viral receptors on other cells, and the relative rates of immune induction and release of infectious virus particles. Localized infections in the epithelium are usually limited by the physical constraints of the tissue and are brought under control by the intrinsic and innate immune defenses discussed in Chapter 3. An infection that spreads beyond the primary site (usually near the point of viral entry) is said to be disseminated. If many organs are viral targets, the infection is described as systemic. Spread beyond the primary site requires continued breaching of the host’s physical barriers. For example, virus particles may be able to cross a basement membrane when the integrity of that structure is compromised by inflammation and epithelial cell destruction. Below the basement membrane are subepithelial tissues, where virus particles encounter tissue fluids, the lymphatic system, and phagocytes. These host components make substantial contributions to clearing foreign particles, but may also allow infectious virus particles to be carried beyond the primary site of infection.

      DISCUSSION

       Gender differences in infection and disease

      Male and female humans differ in both their susceptibility to infection and in the severity of illness that some infections can cause. In general, males become infected more often than females, likely because females often mount stronger immune responses than males. However, while these responses can result in faster resolution of the infection, they can also contribute to immunopathology, which is seen more in women than men. Adverse reactions to both vaccines and antiviral drugs are also greater in women than in men, perhaps as a result of gender-based differences in hormone type, as well as differences in the metabolism of drugs and vaccines.

       Klein SL. 2012. Sex influences immune responses to viruses, and efficacy of prophylaxis and treatments for viral diseases. BioEssays 34:1050–1059.

image

      When spread occurs by neural pathways, innervation at the primary site of inoculation determines which neuronal circuits will be infected. The only areas in the brain or spinal cord that are targets for herpes simplex virus infection are those that contain neurons with axon terminals or dendrites connected to common sites of inoculation in the body. Reactivated herpes simplex virus uses the same neural circuits to return to those sites, where it causes lesions (for example, cold sores in the mouth).

image

image