02 - January 16, 2013.docx

10 Pages
Unlock Document

University of Toronto St. George
Cell and Systems Biology
Gray- Owen

02 – January 16, 2013 Virus infections in humans Important considerations in the viral life cycles Characteristics of the virus – HIV infection Genital tract – acquired there, shed in genital secretions Mucosal events during transmission – every body surface is covered by epithelium, squamous or This layer protects from pathogens – infectious agents must transverse this Ex. Ulcer – caused by herpes – ulcers in mucosa, then virus can pass the layer HIV – surface of virus binds to antigen presenting cells’ receptors, dendritic cells, which are constantly sampling the environment – reaching processes through epitheial layer – virus attach onto the dendritic cell sudopode and enter the virus through receptor on dendritic cell – allows to bypass mucosal barrier and infect CD4 T cells DC SIGN – receptor – gp120 binds to DC SIGN Receptor identifies sugar molecules on pathogens – gp120 covered with sugar – get into dendritic cell Bypass epitheilium Three types of general patterns found in viral infections Amount of virus present in host over time Type 1 – Type 2 – ex. Herpes – initial infection; infection cleared but virus able to enter certain cell poplations that prevents them from immune attack Type 3 – initial infection; infection partially controlled by virus continues to replicate; Viruses that cause type 1 – often more damaging to tissues than viruses of type 2 and 3 If damaing to tissues and type 3 virus – then hos probably will die Viral life cycles in the host are important for understanding how the host responds to various virus infections EB virus infects B cell – when first infected with EV Virus transmitted through saliva – called fomite – mucosa of the mouth and then start infecting other B cells – multiple different stages in B cell – in some B cell, can infect B cell and produce lots of virus particles and in other B cells, depending on which proteins virus produces, remain latent in B cells. EBV manifestations – syndrome – fever, large lympho nodes Rash usually sign of systemic virus infection Infectious mononucleosis – saw cells in blood where nuclei were large and prominent nucleoli and prominent cytoplasm – called atypical lymphocytes – CD8 T cells actually; their presence activated to kill the virus-infected cells HIV and cytomegalovirus can cause these Do FACS anakysis Stereotypic immune response to viruses is depicted here Usually have induction of generic immune response – innate immune response – if innate doesn’t clear the infection – then have priming of adaptor immune response – interferon alpha – if do not clear the infection, then have activation of T cell and antibody response lastly – antibody response is last that fully develops – antibody response is not developed 1 to 2 months after infection Protective capacity of various adaptive immune responses in viral infections Do different viruses need differnet arms of immune system to control…? One general rule: if have virus that is cytopathic (causes tissue damage) – antibody resposnes important in controlling the infection If virus infection is NOT cytopathic – cellular immune responses seem more important Reason: virus in cells hidden from antibodies; cytopathic virus needs to be neutralized fast, which antibodies work; mothers transmit immunity to children via antibodies, IgG, not T cells – so baby had maternal repertoire of IgG, which lasts for first six months of life – when baby is exposed to cytopathic viruses for the first six months of life – Virus subversion Players of the innate immune response – interferons important because interferon Cells degrade virus nucleic acids Main pathways that activate interferon are toll like receptor pathway TLR on surface of cell or endosomes – If virus gets through endosome – into cytoplasm of cell – RLR activate interferon system – adaptive immune responses – viruses have been found that can actually subvert every aspect of his pathway Virus infected host cell Induce resistence to virus replication in cell by activating enzymes in cell – can activate dendritic cells to start priming the adaptive immune response – Different pathways – Differnet types of nucleic acids activate differnet TLR receptors Most pathways trigger INF beta first, then IFB beta signals to trigger interferon alpha Influenza NS1 protein – blocks RIGI – hepatisis C activates downstream of RIGI by breaking endosomal attachment between ISP1 and STING that prevents signalling to make IRF3 RLRs sentinels for non-self RNA RIGI – major cytoplasmic detectin pathways – RNA must have capped at 5’ triphosphate – normal mRNA isn’t capped at 5 prime triphosphate motif – so normal RNA of cell doesn’t activate the pathway HIV also lacks this – so doesn’t activate RIGI pathway Human hepatitis type C virus evades the RIG-I pathway Uses protein complex NS3 4 A – form complex that anchor on membrane and on mitochondria membrane to cleave IPS-1 to prevent RIGI downstream effects HCV can also affect TLR signalling and IFN a/b receptor signalling HCV myriad effects on immune response To block NS34A – binds to HCV protease and prevents from binding to target protein – inhibits HCV replication in vitro – use hepatocyte cell line Telapavir tends to enhance interferon Blocking virus trying to evade innate immune response – Most important immune arm – CD8 T cell – cytotoxic – kill virus infected cell – infected cell four hours to twenty-four hours – during interval – some proteins are chopped up and presented to MHC T cell Granzyme and perforin secreted to kill the infected cell Virus specific CD8 T cell – tetramer technology – take petide and MHC associated with peptide and put in tetramer type – tetramer configuration allows – also indicator dye on streptavidin – configuration enhances the avidity for the reagent for the T cells – see flow cytometry – tetramers used Epitopes against CMV – CD8 responses – usually epitope is dimers to bind with these common HLA – biochemically easy to make CD8 responses in experimental murine virus infections LCMV – RNA virus; Armstrong and Clone 13 strains LCMV infection of Balb c or C57 mice – BALB c mice infected with Armstrong strain – able to clear the virus – after infection, induction of CD8 responses against different epitopes against LCMV – high levels of tetramer staining that is seen Quantitating the magnitude of the lymphocytic choriomeningitis – Huge expansion of CD8 T cell after LCMV infection Majority of cells found in spleen actually targeting LCMV – see huge expansion of CD8 T cells – replace most of T cells pre-existing Found that CD8 T cells could divide about 15 times during cycle of infection Broad immune response Granzyme levels produced NK cells – in context of MHC downregulation – downregulate MHC class 1 in cases of some viruses, so NK cell activated – complicated activation; still do not know stimulating ligands that derived from differnet viruses NK receptors – What about human infections EB virus – similar to acute LCMV – huge expansion of CD8 T cells during mono Huge number of EBV specific cells in blood Follow the patients over time – decreasing levels in blood with time, correlating with levels of antigen in the blood What is the role of CD4 cells in immunity – classical experiments done to address how important CD4 cells are in immune response. In upper diagram – mice infected IP – virus cleared Same with anti-CD4 antibodies so no CD4 cells – no clearance; weak CTL response, there is something wrong with the CTL that are present CD4 generates strong CD8 response CD4 cell contact with APC – presenting virus – CD4 cell activated by dendritic cell – CD4 cell then express surface olecule CD40 ligand CD40 ligand Signal activates DC – upregulate more MHC molecules, more co-stimulatory molecules, more cytokines – all in combination allow activate T cell better Prove in vitro by showing that in humans – when culture CD8 T cells, CD4 T cells ET ratio – killing assay – HIV peptides from HIV infected person – chromium release assy B cells coated with peptide of interst and chromium – if CD8 T cell kills – more chromium released, more killing occurs – assay in different ratios of CD8 CD4 cells present – total PBMC – if deplete CD4 cells – killing goes down – CD4 cells to help CD8 kill their targets CD4 depleted CD8 and then add CD40 ligand – stimulate dendritic cell – replace fnction of CD8 t cells Effector:target ratio; effector is and target is B cells Higher effector target ratio – more killing Conclusions – CD4s important for helping CD8 responses Contradictory papers/findings – general consensus – if CD4 present, allow CD8 to survive better after second exposure to pathogen – Clear pathogen – levels go down; if CD4 cells present, CD8 enhance numbers CD4 important for chronic virus infections; for initial infections, For acute virus infections, do not really need CD4 help If chronic infection, need CD4 help to control the virus Antibodies play a role – antibodies ore induced strongly after _____ expanded Prevent re-infection B cells became plasma cellsl – bo into the bone marrow – plasma cells keep producing antibody Also for chonic virus infections – development of antibodies important HIV – tupe 3 pattern Anything below five hundred is below If have CD4 count of less than two hundred – diffuclty in controlling infections in general – CD4 count is threshold where cannot provide help of other immune responses First virus encounter – high levels of virus in the blood – CD4 – at this time, virus goes down by many logs – partial control by the virus during the infection Infected person can experience infectious mononucleosis Causing the reduction around 6 weeks – innate immunity controlling the virus; experiments include stain for NK cells, measure of level of interferon in plasma, indirect measure of interferon; measured CD8 expansion directly correlates with decline Antibody response develops around 1 year sage – Set point – constant level of virus replicating in blood – five to ten years, no symptoms; active virus replication in blood; CD4 counts decrease; by year 8, CD4 cells less than four hundred – imunosuppressio – CD4 What’s causing CD4 decline – studied kineets of virus in response to treatment – where is virus coming from – mathematicians Model of dynamics of HIV 1 infection in vivo – average HIV infected person makes 1 billion new viruses per day based on measuring virus in plasma, amount of plasma in a person Ost of virus infecting CD4 T cells and that means everday, a bllion new viruses infect new CD4 T cells – new viruses are dying so new CD4 T cells need to be infected Huge turnover Minority of viruses go ito cell populations tht are not dying 10 thousand base pairs – typical To replicate, needs polymerase trascriptase hat has an rror – so every new lfogey then progeny virus is different form preceding viruses by at least one nucleotide Every site of the of the genome can have at least ten thousand mutations – every region of the virus can have a mua=tations If immune system must target one epitope – easy for virus to be present that doesn’t hae epitops Immune response to HIV Stronger immine response – better able to control the virus – differnet patients hae differet levels in boodle follow thes====HIVEpo] Legend – viral copies per ml plasma Which HIV infected epoeplw dwould progress faster If progressing to AIDS is eual to CD4 count of 200 – Olderyou get, fewer T cells available to fight newer infections – when get older, get HIV infection, won’t handle virus very well – not many T cell responses that can handle new epitopes – T cell will get deleted if srong interaction in thymus – Children response from maternal AIDS patient CD8 in HIV infection Preliminary data suggesting CD8 important for virus control – SIV is simian HIV – monkey model of HIV infection – rhesus macaque – when rhesus macaques given SIV – develops AIDS within 1, 2
More Less

Related notes for CSB202H1

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.