Читать книгу Principles of Virology - Jane Flint, S. Jane Flint - Страница 107

The study of replication cycles of many viruses with one-step growth analysis has allowed a reductionist approach to understanding and defining the steps of virus attachment, entry, replication, and assembly. In contrast, new experimental and computational tools permit global analysis of viral, cellular, and host responses to infection. Global analyses apply a dizzying array of different high-throughput technologies to measure system-wide changes in DNA, RNA, proteins, and metabolites during virus infection of cells, tissues, or entire organisms. Data obtained from high-throughput measurements are integrated and analyzed using mathematical algorithms to generate models that are predictive of the system. For example, virus infections of different animals are characterized by the induction of distinct sets of cytokine genes, a property that can be correlated with different pathogenic outcomes. When a model has been developed, it can be further refined by the use of viral mutants or targeted inhibition of host genes or pathways. Global analysis is therefore a holistic, host-directed approach that complements traditional methods for studying viruses.

Figure 2.19 One-step growth curves of animal viruses. (A) Growth of a nonenveloped virus, adenovirus type 5. The inset illustrates the concept that viruses multiply by assembly of preformed components into particles. (B) Growth of an enveloped virus, Western equine encephalitis virus, a member of the Togaviridae. This virus acquires infectivity after maturation at the plasma membrane, and therefore, little intracellular virus can be detected. The small quantities observed at each time point probably represent released virus contaminating the cell extract.

Examples of global analyses include genome-wide transcriptional profiling to study the host response to infection. Introduction of the 1918 strain of influenza virus into mice leads to a rapidly fatal disease characterized by sustained induction of proinflammatory cytokine and chemokine genes. Understanding the gene expression signature that correlates with lethality is one goal of these studies. Global analysis can also predict signatures of vaccine efficacy. In one study, transcriptional profiling of peripheral blood mononuclear cells from vaccinated subjects revealed that the yellow fever virus vaccine induces the expression of genes encoding members of the complement system and stress response proteins. This pattern accurately predicts CD8⁺ T cell and antibody responses that are thought to mediate protection from infection with yellow fever virus. A separate signature that accurately predicts neutralizing antibody synthesis during infection was also identified.

Some of the methods used in global analysis are described below.