Immunity to virus
- 1. IMMUNITY TO VIRUSES Presented By Tukendra Verma
- 2. Viruses • Obligatory intracellular pathogens that replicate within cells. • Use the nucleic acid and protein synthetic machineries of the host cell. • infect a variety of cell populations by utilizing normal cell surface molecules as receptors to enter cell.
- 3. Innate Immune Response to Viruses 1. Induction of Type I interferons interferons are antiviral protein or glycoprotien produced by several types of cells in response to viral infection. IFN- α by leucocytes IFN- β by fibroblast IFN- γ by NK cells Source -http://www.nature.com/nri/journal/v15/n2/fig_tab/nri3787_F2.html?foxtrotcallback=true
- 4. Mechanism of activity of interferons I Source – owen kuby immunology chapter 5, fig. 16
- 5. 2. Activation of Natural Killer (NK) cells The binding of IFN-alfa and IFN- beta to NK cells induces lytic activity, making them very effective in killing virally infected cells. The activity of NK cells is also greatly enhanced by IL-12, a cytokine that is produced very early in a response to viral infection Source - http://www.nature.com/nri/journal/v5/n11/fig_tab/nri1711_F2.html
- 6. Specific Immune Response To Viruses • Humoral mediated immune response • Viral Neutralization by Humoral Antibody • i.e. Secretory IgA in mucous secretions • Viral Neutralization by antibody sometimes occurs after viral attachment. • Block viral penetration.
- 7. Specific Immune Response to Viruses • Activated Th1 cells produce several cytokines IL-2 Acts indirectly by assisting the development CTL precursors Activates NK cells IFN-γ Directly induces an antiviral state in near by cells Activates NK cells TNF • CTL activity Arises within 3-4 days after infections Peaks by 7-10 days, and then declines Have viral specificity Eliminites specific virus- infected cells, thus getting rid of potential new sources of new virus • Cell-mediated immune response
- 8. Cell-mediated immune response • Antiviral CTL responses occur in 4 phases • 1. Induction phase • 2. Activation-induced cell-death (AICD) phase • 3. Silencing phase • 4. Memory phase
- 10. Viruses Can Evade Host Defence Mechanism 1. Inhibition of humoral immune response Antigenic variation • Generation and selecton of varients with different antigenic properties • Genetic variability • e.g.- influenzae virus & HIV source -http://www.ppdictionary.com/viruses/flu_a.htm
- 11. complement inactivation • virus encode homologous protein to regulatory complement compnents • blocks secertion and activation of complement system. • e.g.- HIV, CMV & VV. fc receptor encoding • virus encodes fc receptors • antibody bound infected cells bound to virus encoded fc receptors
- 12. 2. Interfernce with interferons type I interferons (α, β) • virus block JAK-STAT pathway which block interferon activity. • inhibition of interferon effactor pathway by inhibiting the PKR. • encoding soluble interferon receptors block functions of interferons. type II interferons (γ) • block the synthesis of (γ).
- 13. Some developed the strateries to avade the action of IFN-α & IFN-β.
- 14. 3. cytokine inhibition • block cytokine expression e.g.- ASFV- encode IkB • block signal transduction • mimicry of cytokine and its receptor for its benefit • secreting cytokine receptor homolog
- 16. 4. Some inhibit the antigen presentation • i.g.- HSV viruses • HSV-1 and HSV-2 both express an immediate-early protein called ICP47. • Inhibits the human transporter molecule -TAP. • Inhibition of TAP blocks antigen delivery to class I MHC receptors on HSV-infected cells, thus preventing presentation of viral antigen to CD8+ T cells. • Some down-regulate class I MHC expression i.g.-adenoviruses and cytomegalovirus.
- 17. 5. Inhibition of apoptosis