What is a virus?
an infective agent that typically consists of a nucleic acid molecule in a protein coat, is too small to be seen by light microscopy and is able to multiple only within the living cells of a host
What is the programme viruses have to self-replication and multiplication?
gene expression; genome replication; virus assmebl; virus release and transmission
how are viruses classified?
Baltimore classificaation: type of genoma and method of replication
Give examples of dsDNA viruses?
herpes; poxvirus; adenovirus; papillomavirus
Give examples of ssDNA viruses?
adeno-associated virus
Give examples of dsRNA viruses?
reovirus
Give examples of negative ssRNA viruses?
influenza
Give examples of positive ssRNA viruses?
poliovirus; hep A and C
Give exaample of reverse RNA virus?
HIV
Give an example of a reverse DNA virus?
hep b
Give an example of a cytopathic virus
hep B
Give an example of a non-cytopathic virus?
rhinovirus
What is involved in immmunity against chronic viruses?
T cells
what is involved in immunity against acute viruses?
neutralising antibodies
What aer the features of barrier protection against infection in the skin?
epithelial cells joined by tight junctions; longitudinal flow of air/fluid; fatty acids; antibacterial peptides; normal flora
What are the type III interferons?
IFN delta 1,2,3
What are the functions of type I and type III IFNs?
induce antiviral repsonses and limit viral replication
Which cells are IFN receptors found on?
all nucleated cells
What do NK cells secrete to lyse cells?
perforin and granzyme B
What activates invariant and unconventional T cells?
lipids; microbiota metabolites or cytokines
What are the types of invariant and unconventional T cells?
NKT; MAIT and yd T cells
How is infection related to viral load and T cell response?
infection occurs at the same time as T cell reponse not at the peak of the viral load
How are antibodies invovled in the removal of viruses?
coat infected cell which leads to ADCC by NK cells; activate complement; opsonise for phagocytosis
Which cells are specialised for production of type I IFns?
plasmacytoid DCs
What is the function of Th1 cells in viral responses?
provide help for opsonising and complement fixing virus specific abs that block entry into uninfected cells and activate complemetn to destroy enveloped viruses
Why do RNA viruses have a higher rate of replication than DNA viruses?
have to replicate their genoma using RNA polymerase which lacks the proofreading ability of DNA polymerase
What is the benefit of RNA polymerase for RNA viruses?
high rate of mutations allows them to change the antigenic epitopes recognised by the adaptive immune system
Aside from RNA polymerase, what other mutation mechanism do RNA viruses have?
segmented genomes which they can rearrange during viral replication
What are the major viral surface glycoproteins?
haemagluttinin and neuramidase
What is antigenic drift?
point mutations which change the epitopes on the viral surface glycoproteins recognised by adaptive immune system
What is antigenic shift?
antigenic chanegs in virus that result from reassortment of hte segmented RNA genome between 2 different versions of a virus in a secondary host and result in major changes in the haemagglutinin ex[ressed
Waht is the benefit for DNA viruses not having such a high rate of mutations?
can support a much larger genome that can subvert many aspects of antiviral defence
What protein do many DNA viruses produce that prevents presentaiton of peptide:MHC I complexes?
immunoevasins
Waht is dislocation?
viral proteins taht catalyse the degradation of newly made MHC-I complexes which activates the pathway normally used to degrade misfloded ER by directing them back into the cytosol (ERAD pathway)
How does EBV cause immunosuppression of the host?
produces a homolog of IL10 which inhibits Th1 cells and IFNy production
How can viruses evade NK cells?
producing a homolog of MHC-I which binds to KIRs and LIRs providing an inhibitory response
What are cells with immune exhaustion characterised by?
expression of PD-1
What receptor does EBV use to gain access to B cells?
CR2 (CD21)
What is the function of EBNA1 in latent EBV infection?
interacts with the proteasome to prevents its viral genome from being degraded