B Lymphocyte Effector Function Flashcards
describe how B lymphocytes (plasma cells) actually function
plasma cells only secrete antibody and B cell functions are simply the function of antibodies, but antibodies only perform functions when bound to antigen, and so it is actually the antigen/antibody complex that results in the effect functions of B lymphocytes
what determines the function of antibodies?
the antibody class
what are Fc receptors?
a diverse group of receptors that bind to different antibody classes and are expressed by many different cells
how do Fc receptors work?
Fc receptors bind to the Fc fragment of antibodies and signal to initiate functions of antibodies when an antigen/antibody complex binds to them
what are the 6 effector functions of antibodies?
- neutralization
- agglutination
- opsonization
- complement activation
- antibody-dependent cell-mediated cytotoxicity
- antibody-activated degranulation
describe the nuetralization function of antibodies
antibody blocks entry of pathogen into cells
describe the agglutination function of antibodies
clumping of antigen; multiple antigens will bind to antibodies, creating clumps that help with neutralization and help to clear the antigen from the body
describe the opsonization function of antibodies
mark antigen for phagocytosis; occurs as the antigen/antibody complex binds Fc receptor on phagocytic cell (macrophage or dendritic cell) and this initiates phagocytosis
describe the complement activation function of antibodies
antibody-antigen complexes activate complement via the classical pathway
describe the antibody-dependent cell-mediated cytotoxicity function of antibodies (3)
- antibody will bind to Fc receptors on natural killer cells
- antibody on NK cell will bind to antigen on infected cells and the antigen/antibody complex will signal for cytotoxicity
- NK cell will kill infected cell
describe antibody-activated degranulation
antibody-antigen complex binds to Fc receptors on granulocytes, resulting in release of contents of cytotoxic granules
in what two cases is antibody-activated degranulation important?
- parasitic infections
2. allergies
what 3 antibody effector functions require binding through Fc receptors?
- opsonization
- antibody-dependent cll-mediated cytotoxicity
- antibody-activated degranulation
what is the only class of antibody that is not secreted and is instead only membrane bound and found during development and activation?
IgD
in what structure is IgM secreted and when?
as a pentamer at the beginning of an adaptive immune response
what cells secrete IgM?
plasma cells from the primary focus that have not gone through somatic hypermutation
what 2 effector functions can IgM perform and which of those is it GREAT at and why?
- can activate complement
2. is best at agglutination because pentamer structure means it can bind and clump 10 antibodies at once!
due to its structure, what effector functions can IgM NOT perform and why?
cannot perform any of the functions requiring binding of Fc receptors. This is because due to the pentamer function, the Fc region of IgM in unavailable for binding
(so can’t do ADCC, opsonization, or degranulation)
in what structure is IgG secreted?
as a monomer
what is the most common class of antibody in serum?
IgG
is IgG in the same form for every species?
no, there are different forms of IgG for all species
what 3 effector functions is IgG really good at?
- opsonization
- antibody-depedent cell-mediated cytotoxicity
- complement activation
in serum, what structure is IgA secreted as?
monomer
in body secretions, what structure is IgA secreted as?
dimer
what is the main class of antobody found in secretions such as tears, salive, mucus, and milk?
IgA
what are the major function of IgA in secretions?
- neutralization to prevent pathogen entry into body
2. agglutination: to make it easier for the secretions to wash the pathogen out of the body
what is a third function that IgA performs in blood?
anitbody-dependent cell-mediates cytotoxicity
in what structure is IgE secreted and when?
as a monomer in parasitic and allergic infections
what is the main funciton of IgE?
degranulation
