10. immunity to viruses Flashcards
where in the viral cell cycle can the immune system act?
anti-viral effects of antibodies
strategies directed at extra cellular viruses
•Antibody
- blocks binding and entry to cells
- activates intra-cellular degradation via TRIM21
•Antibody + complement
- damage to enveloped viruses
- opsonisation for phagocytosis
•Antibody bound to infected cells
- antibody-dependent cellular cytotoxicity
antigenic drift
gradual changes in teh virus due to accumulation of point mutations
eg. influenza virus has evolved to change antigenic nature so antibodies cannot recognise the other strain
antigenic shift
dramatic change in antigen due to recombination between different strains of the virus
two different strains simultaenously infect cells, as getting replicated in the same cell, genetic info swapped- no herd immunity- major pandemic infections, new strain arises
strategies for intra-cellular viruses
anti-viral action of interferon
Type 1 interferon enhance expression of HLA class I proteins and activate NK cells and Tc
- virus infection triggers infected cells to release IFNa/ß
- IFN also induce enzymes that degrade viral mRNA
difference between T cells and NK cells
NK cells do not express clonally distributed antigen specific receptors
NK also known as large granular lymphocytes
Two mechanisms of NK cells
- Antibody dependent cellular cytotoxicity
- IgG ab bind to native viral antigens expressed on infected cells (NK express Fc for IgG)
- bind to infected cell then kill
- native viral proteins which IgG bind to are expressed on the surface of infected cells during assembly of eveloped virus, portion of cell surface membrane incorporated into virus
- No direct interaction with virus
- NK cells express receptors that interact with other cells which can inhibit or activate NK cells to kill
- inhibitory receptors are dominant to avoid killing normal cells
- NK inhibitory receptors interact with HLA class I expressed by normal cells
some viruses induce down modulation of HLA I expression thus reduce targets for killing by Tc but more likely to be killed by NK
NK cells are not involved in adaptive immunity
mechanism to bring about cell destruction by Tc and NK
induction of target cell apoptosis
how does NK cells induce apoptosis
granules with two types of proteins:
1. perforins polymerise and form tubular structures (like C9 complex) - punch hole, granzymes gain entry into cytoplasm and activate caspase to initiate apoptosis
- surface protein: Fas-ligand that interacts with Fas protein on target cell surface: activates apoptosis
which IFN does NK cells produce
IFNγ: anti viral activity and enhances HLA I and II expression
