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antigen-presenting cell (APC) 54 antigen retrieval
T cell
receptor
Processed
antigen
Histotope
T cell
Antigen-presenting cell.
MHC molecules is critical to the development of an appropriate
immune response.
antigen-presenting cell (APC)
A cell that can process a protein antigen, break it into peptides,
and present it in conjunction with major histocompatibility
complex (MHC) antigens on the cell surface where it may
interact with appropriate T cell receptors. Professional antigenpresenting
cells include dendritic cells, macrophages, and B
cells that are capable of initiating T lymphocyte responsiveness
to antigen. These cells display antigenic peptide fragments
in association with the proper class of MHC molecules and
also bear costimulatory surface molecules. Dendritic cells
are the most important professional antigen-presenting cells
for initiating primary T lymphocyte responses. This process
is facilitated in part by their continuous high level expression
of costimulatory B7 molecules. Dendritic reticulum cells,
macrophages, Langerhans cells, and B cells process and present
antigen to immunoreactive lymphocytes such as CD4 + T
helper/ inducer cells. An MHC transporter-gene-encoded peptide
supply factor may mediate peptide antigen presentation.
In addition to the three types of professional APCs mentioned
above, follicular dendritic cells are the main antigen-presenting
cells for B cells. Non-professional antigen-presenting cells
include keratinocytes and selected epithelial, endothelial, and
mesenchymal cells and can act as antigen-presenting cells
when activated during inflammation. Antigen-presenting
cells include those that present exogenous antigen processed
Cell type
Dendritic cells
(Langerhans cells,
lymphoid dendritic
cells)
Macrophages
B lymphocytes
Vascular
endothelial cells
CD4
MHC class II
molecule
Class II
Inducible by
IFN
Inducible by
IFN
in their endosomal compartments and are presented together
with MHC class II molecules. Other antigen-presenting cells
present antigen that has been endogenously produced by the
body’s own cells with processing in an intracellular compartment
and presentation together with MHC class I molecules.
A third group of APCs present exogenous antigen that is taken
into cells and processed followed by presentation together
with MHC class I molecules. In addition to processing and
presenting antigenic peptides in association with MHC class
II molecules, an antigen-presenting cell must also deliver a
costimulatory signal that is necessary for T cell activation.
Nonprofessional APCs that function in antigen presentation for
only brief periods include thymic epithelial cells and vascular
endothelial cells.
antigen processing
The degradation of proteins into peptides capable of binding
in the peptide binding groove of MHC class I or MHC
class II molecules for presentation to T lymphocytes. For
presentation by MHC molecules, antigens must be processed
into peptides.
antigen receptor
Cell surface immunoglobulin for B cells and T cell receptor
for T cells. A single antigen specificity is expressed on the
surface of each lymphocyte.
antigen recognition activation motif
A conserved sequence of 17 amino acid residues that contains
two tyrosine-X-X-leucine regions. This motif is found
in the cytoplasmic tails of the FceRI-b and -a chains, the z
and h chains of the TCR complex, the IgG and IgA proteins
of membrane IgD and IgM, and the α, δ, and ε chains of
CD3. The antigen recognition activation motif is thought to
be involved in signal transduction.
antigen retrieval
A novel method for the rescue of antigens from formalinfixed,
paraffin-embedded tissue. It consists of heating
sections in a microwave oven or pressure cooker in the
presence of an antigen retrieval solution. It is designed for
use in immunohistochemical staining with certain antibodies.
This technique increases staining intensity and reduces
background staining of many important markers in formalinfixed
tissue. Its use helps overcome false-negative staining
of overfixed tissue, expands the range of antibodies useful
Costimulators
Constitutive Constitutive
Inducible by
LPS
Constitutive Constitutive
Constitutive
Properties and functions of antigen-presenting cells.
Principal functions
Inflammation of CD4 *
T cell response;
allograft rejection
Development of CD4 *
effector T cells
Stimulation by CD4 *
helper T cells in
humoral immune
responses
Recruitment of antigenspecific
T cells to site
of antigen exposure
or inflammation