Exam 2- Immunity to Intracellular Pathogens Flashcards
what does it mean for an infectious agent to establish a focus of infection?
adheres to epithelial surface, the colonizes it or penetrates it to replicate in the tissues
true/false: disease can only occur AFTER the infectious agent is not eliminated by innate immune response
true
how do extracellular pathogens get around the body?
lymphatics or blood vessels
how do intracellular pathogens get around the body?
direct transmission from one cell to another or release into the extracellular fluid and reinfection of adjacent and distant cells
what is the principle mechanism of innate immunity against viruses?
type 1 interferons and NK cell-mediated killing of infected cells
what do type 1 interferons (IFN-alpha and IFN-beta) do to protect against viruses?
cause neighboring cell to synthesize some enzymes to interfere with viral transcription and replication
“antiviral state”
what receptors do NK cells have?
both activation and inhibition receptors
when does the adaptive immune response against viruses begin?
day 4 until end of infection
what mediates the adaptive immune response?
antibodies and cytotoxic lymphocytes
what do antiviral antibodies function as?
neutralizing antibodies
does IgM or IgG have a longer half life?
IgG
true/false: influenza virus can evade innate immunity by mutating hemagluttinin antigen expressed on its surface
false: evading adaptive immunity
what proves that cytotoxic lymphocytes are important with viral infections?
animals deficient in CD8+ T cells are more susceptible to viral infections
how can viruses escape neutralization by pre-existing immunity?
point mutations (antigenic drift) and reassortment of RNA genomes (antigenic shift)
how do viruses evade immune mechanisms in general?
antigenic variation
downregulation class I MHC molecules
produce immunosuppressive molecules
may infect and kill immunocompetent cells
equine herpes virus-1 (EHV-1): hides in trigeminal ganglion
true/false: macrophages kill all bacteria
false: some can readily grow inside macrophages
true/false: if a bacterial pathogen is present in the cytosol of a host cell, the infected cell is killed by cytotoxic T cells
true
how do intracellular bacteria evade immune mechanisms?
blocking phagosome-lysosome fusion
disruption phagosome membrane and escape into cytoplasm
resistant cell wall
how does neutralizing systemic viruses compare to neutralizing mucosal viruses?
systemic: IgG and IgM most important
mucosal: IgA plays a major role in blocking viruses from attaching with mucosal epithelial cells
is complement a major part of defense against viruses?
no
how does antibody-dependent cell-mediated cytotoxicity work?
mediated by natural killer cells
IgG coats virus infected cells and these get bound to NK cells through Fc receptors
NK cells destroy through perforin-dependent killing mechanisms
what is the most important host defense after the virus infection has occured?
cytotoxic T lymphocyte response
what is antigenic drift?
point mutations
what is antigenic shift?
reassortment of RNA genomes
what is antigenic variation?
viruses altering their genomes
what allows influenza virus to survive in a population?
antigenic drift
what cytokines do viruses encode molecules against?
IFN-gamma, TNF, IL-1, and chemokines
do some viruses produce immunosuppressive cytokines?
yes
what is protection against intracellular bacteria mediated by?
cytotoxic T lymphocyte and T helper cell responses
