lecture 3- subversion of immunity Flashcards
the ideal immune response ___ for different pathogens
differs
name 3 pathogens that we deal with
extracellular bacteria
intracellular bacteria
viruses
describe effective immunity to extracellular bacteria
want defenses that work outside the cell- ANTIBODY & COMPLEMENT, which work with phagocytes
- antibody can neutralize and opsonize through Fc receptors
- complement can use phagocytosis, inflammation, and lysis of microbe
- Th17 T helper response favorable because recruits neutrophils
describe immunity to intracellular bacteria
host cells must be activated to kill internal pathogen OR be killed by T cells
- IL-12 and IFN-y (both adaptive and innate)
- IL-12 secreted by macrophages can activate NK cells and Th1 cells
- IFN-y leads to macrophage activation to kill bacteria and is also helpful for CD8 T cells –> killing of infected cell
what cooperation occurs during clearing of intracellular bacteria
cooperation between CD4 and CD8 T cells
describe immunity to viruses
viruses are intracellular
- innate: Type I IFN (antiviral state) (IFN-alpha and IFN-beta) & NK cells
- adaptive: antibody neutralization for protection against infection and CD8 CTL for eradication of established infection
the kinetics of immune response to virus
innate: 0-5 days - Type I IFN’s & NK cells
adaptive: 5-12 days - virus-specific CTL’s & antibody
name 5 strategies pathogens use to survive
1- change what they are “wearing”
2- latency/dormancy
3- disrupt antigen processing and presentation
4- inhibit/suppress innate or adaptive immunity
5- live as a community in a biofilm
describe how pathogens change what they are wearing- S pneumoniae
what is a serotype?
S. pneumoniae come in different serotypes, based on capsule polysaccharides, need different antibody responses for different serotypes
serotype- many bacteria evade host immunity by existing as different strains which differ in the antigenic molecules on their surface
- serological assays used to determine the identity of bacterial strains based on antibodies that bind them
- following infection with a strain, patient will have protective immunity to that strain, but not a different serotype
describe vaccines against S. pneumoniae
they try to include as many serotypes as possible
1- polysaccharide vaccine- consists of purified polysaccharides from 23 diff serotypes
. T-independent, IgM produced
. immunity not as robust or long lasting, but serotype coverage is broad
2- conjugate vaccine- capsular polysaccharide (antibody part) coupled to diptheria toxoid (protein processed & presented to T cells)
. couples B & T cells
. 7-13 serotypes
. T-dependent immunity, B cell memory
. immunity more robust, serotypes more limited
describe how influenza “changes” its clothes to survive
influenza changes its “antigenic clothes” through a process called antigenic drift (small mutations to virus in diff people to evade neutralizing antibodies)
describe difference between antigenic shift and drift
antigenic drift = viruses like influenza are prone to mutations, point mutations in certain antigens are sufficient to alter antibody binding, creating a means of escape from the existing antibody response
antigenic shift = more dramatic changes in the virus in which new recombinant viral genomes are generated in cells infected with 2 distinct viruses (human & avian) - leads to more spread, pandemic
antigenic ___ is more dramatic and results in such a different virus that no one has ____
pre-existing memory
describe strategy of latency/dormancy for how pathogens survive
herpes simplex virus hides from the immune response by entering latency, a dormant state in which replication does not occur
- virus integrates into genome, hide in this state for long period, replication does not occur
- stresses induce reactivation of the virus, upon reactivation, the immune response can respond to viral infection
describe strategy of pathogens inhibiting immune response
Epstein-Barr Virus
- produces cytokine homolog IL-10 that inhibits T helper Th1 response and reduces IFN-y production
describe strategy of pathogens inhibiting antigen processing presentation to survive
viral protein produced by CMV that pulls newly synthesized MHC Class I out of ER and reduces MHC I expression on surface, unable to stimulate CD8 T cells
describe biofilms
surface-attached community of bacteria encased in a polymeric matrix (matrix consists of polysaccharides and nucleic acids)
- protected from a number of stresses or immune defenses
- less sensitive to ROI, phagocytosis, complement, neutrophil attack
- characteristic of many mucosal infection: otitis, pneumonia - Haemophilus influenzae
