3 Recognition of viral infection
To combat a virus infection, the immune system must first recognise the virus, and/or virus-infected cells.
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From your knowledge of the structure and life-cycle of an enveloped virus, identify three distinctive features of a virus or virus-infected cell, that could distinguish it from normal host cells.
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- The virus has proteins encoded by the viral genome which are different from the host proteins, for example the spike protein, haemagglutinin, M-protein or nucleocapsid.
- If a cell is infected by an enveloped virus, then some viral proteins are inserted into the membrane of the cell, before the individual viruses assemble and bud off.
- The genome of influenza-A and SARS-Cov2 is RNA, whereas the genome of mammalian cells is DNA. The replication of these viruses involves dsRNA, which is not a regular component of host cells.
As you will see, there are two major types of immune response – innate immune responses and adaptive immune responses. Adaptive immune responses improve with time, especially following repeated encounters with the same pathogen. In contrast, innate immune responses do not display immunological memory, and hence do not improve significantly over time.
The adaptive immune system primarily recognises foreign proteins, such as virus-encoded proteins. Any biological molecule that can be recognised by the adaptive immune system is called an antigen. We will look at antigen-recognition and adaptive immune responses against viruses in Week 2.
Adaptive immune responses take several days to become fully active. During this early period of infection, the innate immune system acts as a first line of defence. The innate immune system recognises ‘pathogen-associated molecular patterns (PAMPs)’ which are distinctive biological components of bacteria, viruses and fungi. For the rest of this week, you will consider some of these PAMPs and how they trigger innate immune responses to viruses.