Immunology - Host Defense & Immune Evasion Flashcards
What are the three major functions of interferons (IFN)?
- ) Induce resistance to viral replication in all cells
- ) Increase MHC class 1 expression and antigen presentation in all cells.
- ) Activate NK cells to kill virus-infected cells.
What are the two ways the innate immune system is able to distinguish self from non-self?
- ) Pattern recognition receptors (PRRs)
2. ) Missing/altered self receptors (NK cells).
What are the three ways in which the adaptive immune system is able to distinguish self from non-self?
- ) Antigen presentation (MHC)
- ) Antibodies
- ) T cell receptors
What are PAMPs and what is their role?
Pathogen-associated molecular patterns are patterns that are found only in bacteria or other microbes. They are detected when they bind to pattern-recognition receptors which are present on host phagocytic cells.
Which type(s) of microbe(s) do macrophages express PRR’s for?
Bacteria
Which type(s) of microbe(s) do neutrophils express PRRs for?
Bacteria and fungi
Where are reserves of neutrophils stored?
Bone marrow
In which circumstances do eosinophils’ numbers increase?
Parasite infection and in patients with type 1 hypersensitivities. They are a an important defense against helminths.
What causes the increase in NK cells during a viral infection?
interferron
What is the mechanism used by natural killer cells in causing cell death?
NK cells release perforins and granzymes which perforate membranes and trigger caspase-mediated cell death.
Describe the two receptor-binding interactions required for discrimination of self vs. non-self by NK cells.
One receptor is to activate the NK cell to kill, the other is to block the NK cell from killing (MHC 1 receptor). Virus-infected cells express fewer MHC 1 receptors on their surface.
What activates the classical pathway?
C1 binding to the C-reactive protein on the pathogen surface.
What activates the lectin pathway?
Mannan binding lectin (MBL) and MBL-associated serine protease-2 (MASP-2)
What activates the alternative pathway?
Contact of microbial cell wall with C3b
What component(s) of the complement system causes opsonization?
C3b
What component(s) of the complement system causes the activation of the inflammatory response?
C3a & C5a
What is the “formula” for C3 convertase produced by the alternative pathway?
C3bBb
What is the “formula” for C3 convertase produced by the classical and lectin pathway(s)?
C4bC2b
What is the “formula” for C5 convertase from classical/lectin & alternative pathways?
Classical/lectin pathways: C4bC2bC3b
Alternative pathway: C3bBbC3b
Define humoral immunity.
A type of immunity mediated by antibodies secreted by antigen-activated B cells and their progeny plasma cells.
What are the features of secondary humoral immune response as compared with primary?
Shorter lag phase
Greater magnitude
Class-switched to IgG (was IgM in primary)
Define paratopes
The part of an antibody that recognized an antigen. The antigen-binding site of an antibody.
Define epitope
The part of an antigen that is recognized by an antibody.
What are surface immunoglobulins and which type(s) of cells have them?
Antibodies expressed on the surface of certain cells.
B-cells and T-cells have surface immunoglobulins
Which types of cells recognize native antigen proteins without processing? With processing?
B-cell receptors & antibodies recognize native antigen proteins without processing
T-cell receptors recognize only processed antigens when presented on MHC.
Define cell mediated immunity.
Immunity mediated by antigen-activated T cells and the cytokines they secrete.
MHC-class 1:
Which cells have it?
What is its function?
What’s the result?
All nucleated cells have it
It presents antigens to cytotoxic T (CD8+) cells
It results in T cell-mediated toxicity
MHC- class 2:
Which cells have it?
What is its function?
What’s the result?
B cells, macrophages and dendritic cells (antigen-presenting cells)
Present antigen to T (CD4+) helper cells
T cell-mediated help (either cell-mediated or antibody mediated response)
Which class MHC receptor is used in protection against intracellular pathogens?
MHC class 1 AND MHC class 2
Which MHC receptor is used in protection against exogenous antigens?
MHC class 2
What does CD4+ TH1 do when stimulated with an antigen?
Activates macrophage for delayed-type hypersensitivity response.
What does CD4+ TH2 do when stimualted with an antigen?
Activates a B cell for antibody response.
Define ADCC
Antibody dependent cell-mediated cytotoxicity is cell-mediated immune defense whereby an effector cell actively lyses a target cell, whose membrane-surface antigens have been bound by specific antibodies.
What type(s) of cell(s) are capable of ADCC?
NK cells
Macrophages
Neutrophils
Eosinophils
What are the (5) evasion strategies used by bacteria?
Evasion of antimicrobial peptides
Impairement of tracheal clearance
Adhesion and penetration of epithelial barriers
Evasion of phagocytosis
Evasion of complement killing
Beta-defensins are an example of ___.
antimicrobial peptides
What are the (5) ways in which evasion of complement killing can be executed?
Activate masking substances (i.e. capsule, coating with antibodies)
Apply appropriate inhibitors of activation to surface
Cover up target of membrane attack complex
Inactivate complement chemotaxin C5a
Activate surface of plasminogen to plasmin to cleave C3b.
What (7) techniques of immune evasion are used by bacteria to evade adaptive immunity?
Antigenic variation
Apoptosis or lysis of lymphocytes
Inhibition of lymphocyte proliferation
Superantigens
Effects on cytokine expression
Subversion of T regulatory cells
Degradation of immunoglobulins
In what (3) ways are viruses able to avoid detection by the immune system?
Avoidance of exposure - presentation on MHC class 1 receptors is blocked
Location - Hide in an area that won’t be searched (intracellular, brain)
Immunosuppressive viral proteins.
In what (3) ways are viruses able to escape the immune system?
Point mutation - example: influenza has a high mutation rate
Reassortment - complimentary genome segments are switched
Recombination - like reassortment but involving two strains of unsegmented virus.
In what ways (3) are bacteria able to suppress the immune system?
Apoptosis or lysis of lymphocytes
Inhibition of lymphocyte proliferation
Degradation of immunoglobulins
Which groups of pathogens evade the immune system by hiding inside cells?
Bacteria, viruses and parasites
In what ways (5) do parasites evade the immune system?
Antigenic variation
Molecular mimicry - microbial antigens mimic host antigens leading to poor antibody response
Concealment of antigenic site
Intracellular location
Immunosuppression
Which type(s) of antigen(s) use immunosuppresion as an immune evasion technique?
Bacteria, viruses, parasites.
Which type(s) of antigen(s) use antigenic variation to evade the immune system?
Bacteria, viruses (mutations) and parasites.
