Immunology Review Flashcards
What are the important immunoglobulins in antibacterial defense?
IgA, IgM, and IgG
What percentage of immunoglobulins is IgA?
5-15 %
Where is IgA found?
on mucosal surfaces, in colostrum, respiratory and intestinal secretions, tears, saliva, and other secretions
What is the half life of IgA?
6 days
What is the function of IgA?
it can bind to fimbria to prevent adhesion of these bacteria to the mucosal surface and resists proteolytic digestion by intestinal enzymes
What does IgA need help from to produce secretory IgA?
t-cell help
How do bacteria stimulate the production of IgA?
they colonize or invade through mucosal surfaces
What is the predominant immunoglobulin in the bloodstream and tissues?
IgG - 85% of the total
What is the function of IgG?
opsonization and killing of bacteria, and chemotaxis
What is opsonization and killing of bacteria mediated by?
complement
How can IgG opsonize bacteria directly?
by facilitating bacterium-phagocytic contact via the Fc receptor on the phagocyte
What response is IgG the principle antibody in?
the amnestic (booster) response
What is required for the production of IgG?
T-cell help and generation of long term memory cells
What species is IgG the predominant antibody on mucosal surfaces and in milk, colostrum, and intestinal tracts?
ruminants
What is the primary antibody in the early immune response?
IgM
Where is IgM found?
the intravascular space
What is the function of IgM?
fixing complement
In regards to pathogenic bacteria, what is IgM important for?
immunity against polysaccharide antigens on their surface
What stimulates an IgM response (in regards to bacteria)?
bacterial polysaccharides and peptidoglycan because they are T-cell independent antigens
What is the half-life for IgM?
5 days
What percentage of immunoglobulins is IgE?
1%
What is the half-life of IgE?
2.5 days
Where is most IgE bound?
to Fc receptors on mast cells
What happens when antigen binds to IgE?
the cell degranulates and releases histamine, prostaglandin, platelet activating factor, and cytokines
What are the functions of complement?
opsonization and killing
How does complement opsonize?
deposition of C3b onto the bacterial surface enhances the phagocytosis of the bacterium by interacting with receptors on the surface of the phagocyte
How does complement kill?
the end-point of the complement cascade is the formation of the membrane attack complex (MAC) that is capable of lysing susceptible gram-negative bacteria.
What pathways can complement act through?
classical or alternate
Which pathway requires antibody?
classical
What bacterial components are capable of activating the alternate pathway?
LPS, capsular polysaccharides, and other cell wall constituents
What is lactoferrin?
an iron binding protein that is present in milk and many other secretions - its antibacterial effect derives from its ability to limit the amount of iron available for uptake by bacteria
What is transferrin?
a protein that forms a similar function to lactoferrin but in serum
What is conglutinin?
a component of bovine serum that can aggregate Ag-Ab complexes to which complement is bound
What is fibronectin?
a serum protein with a number of binding sites for both bacteria and phagocytic cells; it helps to opsinize
What must be intact in order for gram negative organisms to resist complement?
the complete outer membrane (LPS) and accomanying structures
Which complement pathways can LPS activate?
classical and alternative
Most bacteria associated with invasive infections are _______.
encapsulated
What part of the outer membrane is associated with resistance to complement?
O-Antigen
What does some bacteria produce that is capable of breaking down complement?
peptidases
Are immunoglobulins alone harmless to most pathogenic bacteria?
yes
What may inhibit the MAC of complement (generally)?
some proteins in the cell wall of bacteria
How can bacteria degrade immunoglobulibs?
via trypsin-like enzymes
How may bacteria avoid the immune response?
by infecting sites of the hosts body that have poor defenses (epithelial cells of the respiratory, alimentary, and urogenital tracts, the mammary gland, and the gall bladder)
What is antigenic similarity?
when an organism possesses antigens that are similar to those of the host tissues
What is antigenic shift?
when an organism alters the main component against which the host’s immune response is directed
