Antibodies II Flashcards
Response to an antigen that immune system has never encountered before
Primary Response
Response to an antigen previously encountered
Secondary Response
A primary response is dominated by
-affinity for antibody is low
IgM
A secondary response is dominated by
-affinity for antibody is high
IgG
Larger and longer than primary responses
Secodary response
Allows serological diagnosis of a recent infection
Presence of IgM
If the immune response is dominated by IgM, exposure must have been
Recent
A newborn, because of transplacental transfer of IgG, has antibody to all pathogens previously encountered by its
Mother
Not transported across the placenta
IgM
Neonatal pathogen-specific IgM must have been made in response to exposure in utero and is indicative of
Infection
Class switching is produced by splicing of
Constant-region DNA
The first antibody made in an immune response is always
IgM
In a ‘class switch’ VDJ segments which encode the VH domain are retained, but the DNA that encodes IgM constant regions is
Deleted
The VDJ exon then becomes associated with DNA that encodes an
IgG constant region
Combining site specificity thus stays the same, but the
Isotype changes
The signals in DNA, and the mechanism of splicing, are different from those that assemble
VDJ regions
The new isotype is determined by the size of the DNA segment
Deleted
Heavy-chain constant-region genes are adjacent to one another, downstream from the
VDJ exon
The VDJ segments can become associated with any downstream
-Dependent on the amount of DNA deleted
Constant-region segment
Class switching is
-because once DNA is deleted it can not be regained
Irreversible
Thus a cell which has switched from production of IgM to production of IgG2 cannot go on to switch to production of IgA1, because the DNA of the IgA1 constant region
Gone
Class switching is regulated by
Cytokines
Switching occurs at ‘S regions’ in DNA. These regions must be transcribed to participate in
Switching
Particular cytokines activate transcription of particular S regions, and this in part determines the mixture of isotypes created during an
Immune response
A monoclonal population may represent a
Malignant or pre-malignant state
A polyclonal popultion may represent an
Inflammatory process
