Lecture 11 Viruses Flashcards
What is the structure of a virus
Virus particles are called virions
Viruses have sub particles called capsomeres
Capsomeres surrounded by lipid layer called capsid
An envelope containing lipoproteins surround virion (derived from host)
Describe the process of a viral infection
Adsorption - Bind to receptors
Endocytosis - Virus merges with host cell
Uncoating - capsid broken down and nucleic acid released
Replication of nucleic acid - in cytoplasm and nucleus, host DNA, RNA and protein synthesis halted
Viral nucleic acid form viral proteins
Viral proteins released from cell by cell lysis or budding
How is replication of lentiviruses different to other viruses
Lentivirus infectious viral RNA undergoes reverse transcriptase to Viral DNA then that transcribes to viral RNA
Which immunity is used more in viral infections
Innate short term - interferon mediated
Cell mediated immunity most important as cells are intracellular and humoral releases antibodies extracellularly
What are the four innate immune effector functions
Lysozyme in secretions
Complement
Collectins (Mannose binding lectin) block viral replication
Defensins in leukocytes - break viral envelope
What do Pattern recognition receptors induce in innate immunity to viruses
PRRs induce type I inteferon expression, inflammation and NK cell activation
Describe interferon alpha/beta and gamma
Interferon alpha/beta activate host cells to produce proteins and block viral protein production
Interferon gamma increases efficiency of adaptive immune response
Describe how natural killer (NK) cells help will viral infection in innate immunity and what mediates NK cells
Recognise virus infecting cells as they do not express the same levels of MHC molecules as healthy cells do so they kill them
Interferon alpha mediates NK cell activity
What are interferons, what are the two types and who produces them
Interferons are glycoproteins secreted by virus infected cells
Type I (alpha and beta)
- interferon alpha produced by dendritic cells, macrophages and monocytes
- interferon beta produced by virus infected fibroplasts
Type II (gamma)
- produced by antigen stimulated T cells
What is the role of humoral immunity in viral infections
Viruses are neutralised by antibodies as the Abs can prevent binding to receptors if they are bound.
Antibody protection can also foster opsonization, complement activation and phagocytosis
Describe processing of endogenous antigens and antigen presentation to T cell activation leading to CMI
Virus enters cell, viral peptide is then ubiquinated then chopped by a proteosome. The fragments bind to a transporter protein located in endoplasmic reticulum and then they are bound to MHC class I molecule and then transported to the cell surface The antigen MHC I complex then comes across a TCR on a cytotoxic T cell which then causes destruction of the viral infected cell
Describe processing of exogenous antigens/virus and antigen presentation to T cell activation leading to antibody synthesis
Antigen enters the cell and is then fragmentised by proteases, fragments are then taken to MHC class II molecules and put on the cell surface Th2 cell then binds to antigen MHC complex by TCR and then activates and proliferates and sends B cell growth and B cell differentiation factor to B cells and the B cells either become plasma cells which secrete antibodies or B memory cells. Some Th2 cells become T memory cells also
What do CD4+ helper T cells and CD8+ CTLs do in CMI for viral infections
CD4+ helper T cells secrete cytokines which promote antiviral activity
CD8+ CTLs actively find and destroy virally infected cells
Summary what are the different ways immune system can protect against viruses
Complement (alternative pathway - virolysis, blockage of viral adherence, cytolysis)
Antibodies (Phagocytosis, blockage of viral adherence and virolysis)
Activated macrophages (Phagocytosis, aptosis)
Nk cells (aptosis)
Cytotoxic T cells (aptosis)
What are the 5 ways in which viruses evade immune defences
Antigenic shift and drift
Virokines
Alteration in antigen processing pathways
Evasion of NK cells by downregulating expression of stress related proteins
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