The functionality of cells of the immune system is particularly dependent on
signal pathways, and the various
lymphoid cell types sport an array of
receptors.
▼
antigenic determinant :
APC costimulation :
BCR:
complement receptors :
cytokines :
epitope :
FcR :
Ig-Fc :
IgG :
opsonins :
pathogen associated molecular patterns :
pattern recognition receptors :
phagocyte receptors :
respiratory burst complement :
respiratory burst Fc : :
scavenger receptors :
TCR :
TLR :
Toll-like receptors :
VDJ recombination ▼
PhagocytesPhagocytic cells detect infectious agents that bind to a variety of
receptors on the phagocytes cell membranes, including:
●
Fc receptors (FcR, Ig-Fc) – the constant region (
Fc) of IgG on bacterial surfaces can bind to the Fc receptor on phagocytes. Such binding to the Fc receptor requires prior antibody-antigen interaction. The binding of IgG-coated bacteria to phagocytic Fc receptors stimulates both metabolic activity in the phagocytes (
respiratory burst) and phagocytic activity. Fc receptors include the
clusters of differentiation, CD16 (Fcγ RIII), CD32 (Fcγ RII-A, Fcγ RII-B2, Fcγ RII-B1), and CD64 (Fcγ RI), Fcε RI, and Fcα RI. All FcR are stimulatory except inhibitory Fcγ RII-B1 and B2, which contain immunoreceptor tyrosine based inhibition motifs (ITIMs) in their cytoplasmic tail. Table
Fc receptors●
Complement receptors – Phagocytic cells possess a receptor for the
C3b complement opsonins, and binding of C3b-coated bacteria to this receptor stimulates enhanced phagocytosis and the
respiratory burst. Table
Complement Receptors.
●
Scavenger receptors bind a variety of polyanions on bacterial surfaces, stimulating phagocytosis of the polyanion-coated bacteria. Macrophage scavenger receptors appear to mediate important,
conserved functions, so it was likely
pattern-recognition receptors that arose early in the
evolution of host-defense mechanisms. Table
Scavenger Receptors●
Toll-like receptors are a variety of
pattern recognition receptors (
PRR) that recognize
pathogen associated molecular patterns (
PAMP) on infectious agents. Binding of the infectious agents to Toll-like receptors stimulates
phagocytosis and the release of
inflammatory cytokines (IL-1, TNF-α, IL-6) from the phagocytes. Table
Toll-like ReceptorsTables
Complement Receptors
Fc receptors
Immune Cytokines
Immunoglobulins
Interferons
Scavenger Receptors
Toll-like Receptors .
LymphocytesThe surfaces of
B cells and
T cells are coated with thousands of identical copies of different integral membrane
receptors (
BCRs,
TCRs), each capable of binding with a different
antigen.
Receptor characteristics
● thousands of copies of integral membrane proteins with unique
antigen binding sites
● encoded by genes assembled by
VDJ recombination produced without
antigen encounter
● the
antigen binding site recognizes an
antigenic determinant or
epitope on the
antigen● binding, by non-covalent forces, is based on complementarity of the surface of the receptor and the surface of the epitope
Binding of receptor to epitope, when accompanied by
APC-costimulation, leads to:
●
stimulation of the B or T cell to leave the
G0 phase and enter the
cell cycle● repeated
mitosis generates a clone of cells of identical specificity, each coated with an identical antigen receptor.
Cytokine receptors:
●
Hematopoietin family receptors are dimers or trimers with conserved
cysteines in their extracellular domains and a
conserved Trp-
Ser-X-
Trp-
Ser sequence. The two subunits are i) cytokine-specific, and ii)
signal transducing. Examples are receptors for
IL-2 through
IL-7 and
GM-CSF.
___ ●
Colony-stimulating factors (
CSFs) are glycoprotein molecules that support growth of
hematopoietic colonies. Examples are receptors for interleukin 3 (
IL-3),
G-CSF,
GM-CSF,
M-CSF.
● Interferon family receptorsInterferons are
immune cytokines that are classified, as type I, II, or III, according to the
receptors through which they
signal. Interferon (INF) family receptors have
conserved cysteine residues and include the receptors for
IFNα,
IFNβ, and
IFNγ.
●
Tumor Necrosis Factor family receptors possess four extracellular domains. Examples are receptors for
TNFα,
TNFβ (lymphotoxin β, LT),
CD40,
CD27,
CD30, and
Fas.
●
Chemokine family receptors have seven transmembrane helices (
serpentine,
GRCRs) and interact with
G protein. This family includes receptors for
IL-8,
MIP-1, MCP (monocyte chemoattractant protein), and RANTES (regulated upon activation normal T cell expressed and secreted). Chemokine receptors CCR5 and CXCR4 are used by
HIV to preferentially enter either
macrophages or
T cells.
Tables
Complement Receptors
Fc receptors
Immune Cytokines
Immunoglobulins
Interferons
Cell Adhesion Molecules
Cell signaling
Receptor Tyrosine Kinases (RTKs)
Receptor Signal Transduction
Second Messengers
Scavenger Receptors
Toll-like Receptors
▲ф ф
antibodies ф
antigen :
antigenic determinant ф
APCs :
APC costimulation :
BCR ф
BCR ф
B cells ф
CD ф
cellular response ф
clonal selection ф
complement system :
complement receptors ф
complement system ф
costimulation :
cytokines ~
cytokines ф
dendritic cells :
epitope :
FcR
Fc receptors ф
granulocytes ф
helper T cell ф
hematopoiesis ф
humoral immunity :
Ig-Fc :
IgG
Immune Cytokines
Immunoglobulins □□
Immunology ~
immunoglobulins ф
inflammatory response ф
immune cytokines ф
immune response ф
lymphocytes ф
lymphoid system ф
macrophages ф
MHC :
opsonins ф
pathogens :
pathogen associated molecular patterns (
PAMP) :
pattern recognition receptors (
PRR) ф
pattern-recognition receptors :
phagocyte receptors ф
phagocyte ф
plasma cells :
respiratory burst complement ›››
respiratory burst :
respiratory burst Fc :
scavenger receptors ф
signaling ф
surface receptors :
TCR ф
TCR ф
T cells :
TLR :
Toll-like receptors :
VDJ recombination ▲ф
▲
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Labels: APC, complement, CSF, cytokines, epitope, Fc, lymphoid, phagocytes, receptors, scavenger receptor, Toll-like receptors
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