Immune Recognition II: Adaptive Receptors Flashcards
what are the three types of adaptive receptors?
immunoglobulins
t cell receptors
antigen presenting molecules
immunoglobulins: what produces them, transmembrane/secreted?, what Ag do they recognize?
B cells
transmembrane (B cell receptors) or secreted (immunoglobulins or Ab)
3D surface of proteins, lipids, sugars, nucleic acids, mixture
T cell receptors: what produces them, transmembrane/secreted?, what Ag do they recognize?
T cells
transmembrane
linear fragments of proteins presented on surface of APC
antigen presenting molecules: what produces them, transmembrane/secreted?, what Ag do they recognize?
APC (dendritic cells)
transmembrane
bind peptides and present them at cell surface via MHC or HLA molecules for recognition by TCR
Describe recombination with respect to Ag receptor synthesis/variability.
Different V, D, and J regions are combined and random nucleotides are introduced or changed at the junctions between the segments
the variable region is combined with a constant gene segment (maintain signal transduction/effector fxns)
Give the general structure of immunoglobulins
heavy and light chain with variable and constant region
light+heavy heterodimer (disulfided linked) joins to another to form a homodimer (disulfide linked)
can be soluble or have a transmembrane/cytoplasmic domain
what is the Ag binding site?
light chain domain+heavy chain domain
so two identical Ag binding sites on one immunoglobulin
What does the constant region do?
support Ag binding site
provide interchain disulfide bonds
hinge region allows flexability
Fc fragment has effector fxns, sites for association w/ other molecules for transmission of signals after Ag recognition
What are the five classes of Immunoglobulin isotypes
IgD IgG IgE IgA IgM
Distinguish between the Ig isotypes based off structure
IgD - membrane bound IgG - three heavy domains IgE - four heavy domains IgA - a dimer of two Ig IgM - pentamer of 5 Ig
What are different effector functions of Ig isotypes?
neutralization (block viral particles or toxins from acting)
opsonization (promote phagocytosis)
complement fixation (leading to C3 cleavage)
The Fc region imparts the effector fxn
Activate Fc receptor+ cells (NK, mast) to to respond (cytolysis, histamine release)
Describe general TCR structure
heterodimers (alpha/beta or gamma/delta)
chains linked via disulfide bond
variable and constant domain
always membrane bound
What types of Ag do TCRs recognize?
linear peptide of 8-16 polypeptides presented by MHC
recognizes both the peptide and the MHC 3D surface
what is the CD3 complex?
TCR are always expressed at surface with 4 other transmembrane proteins
fxn - aids in activating intracellular signaling cascades
does BCR act alone?
No.
Igbeta and Igalpha are two signaling subunits associated with Ig.
does a single receptor binding lead to signal transduction?
No.
Ag binding brings brings BCR and TCR together in clusters on cell surface leading to actiavtion of cytoplasmic signaling cascades that lead to translocation of trxn factors to nucleus
what expresses MHC I
all cells except RBC and neurons
what expresses MHC II
only those that interact with T cells
dendritic cells, macrophages, monocytes, B cells
what is the fxn of MHC molecules?
bind peptide fragments and present them on surface of APCs for T cells to recognize
MHC I/II vs. intracellular/extracellular
MHC I = intracellular pathogen source
MHC II = extracellular pathogen source
match up the CD4/8 to the MHC I/II
CD4+ T cells are MHC II restricted
CD8+ T cells are MHC I restricted
Each individual has multiple HLA genes and there are hundreds of different alleles in the population. What two things does this have an impact on?
- Transplantation
2. Disease resistance and susceptibility
