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complement receptor 4 (CR4) 190 complotype
complement receptor 4 (CR4)
Glycoprotein membrane receptor for C3dg on polymorphonuclear
neutrophils (PMNs), monocytes, and platelets. CR4
facilitates Fc-receptor-mediated phagocytosis and mediates
Fc-independent phagocytosis. It consists of a 150-kDa α
chain and a 95-kDa β chain. Chromosome 16 is the site of
genes that encode the α chain, whereas chromosome 21
is the site of genes that encode the β chain. Tissue macrophages
express CR4. It is an integrin with a β chain in
common with CR3 and LFA-1.
complement receptor 5 (CR5)
A receptor that binds C3bi, C3dg, and C3d fragments based
on its specificity for their C3d component. Reactivity is
only in the fluid phase and not when the fragments are
fixed. CR5 is the C3dg-dimer receptor. Neutrophils and
platelets manifest CR5 activity.
The classical and alternative pathways of the complement system.
complement receptors (CR)
Receptors for products of complement reactions.
Proteolytic cleavage of human complement component
C3 takes place following activation of the classical or the
alternative complement pathway. Following the generation
of C3a and C3b, the C3b covalently binds to bacteria,
immune complexes, or other targets and then unites with
a high affinity receptor termed the C3b/C4b receptor and
currently known as CR1. Subsequent proteolytic cleavage
of the bound C3b is attributable to factor I and a cofactor.
This action yields C3bi, C3dg, and C3c, which interact
with specific receptors. CR2 is the C3dg receptor, and CR3
is the C3bi receptor. Proteins on the surfaces of various
types of cells identify and unite with complement proteins
linked to antigens. Phagocyte surface complement receptors
aid the engulfment of complement coated pathogenic
microorganisms. CR1, CR2, CR3, CR4 and C1q receptors
are examples.
complement receptors, membrane
Receptors expressed on blood cells and tissue macrophages
of humans. These include C1q-R (C1q receptor), CR1 (C3b/
C4b receptor; CD35), CR2 (C3d/Epstein–Barr virus [EBV]
receptor; CD21), CR3 (iC3b receptor; CD11b/CD18), CR4
(C3bi receptor; CD11c/CD18), CR5 (C3dg-dimer receptor),
fH-R (factor H receptor), C5a-R (C5a receptor), and C3a/
C4a-R (C3a/C4a receptor). Ligands for C receptors generated
by either the classic or alternate pathways include fluid
phase activation peptides of C3, C4, and C5, designated
C3a, C4a, and C5a, which are anaphylatoxins that interact
with either C3a/C4a-R or C5a-R and participate in inflammation.
Other ligands for C receptors include complement
proteins deposited on immune complexes that are either
soluble or particulate. Fixed C4 and C3 fragments (C4b,
C3b, C3bi, C3dg, and C3d), C1q, and factor H constitute
these ligands. These receptors play a major role in facilitating
improved recognition of pathogenic substances. They
aid in the elimination of bacteria and soluble immune
complexes. Neutrophils, monocytes, and macrophages
express C3 receptors on their surfaces. Neutrophils and
erythrocytes express immune adherence receptors (CR1) on
their surfaces. Four other receptors for CR3 are designated
CR2, CR3, CR4, and CR5. Additional receptors for complement
components other than C3 and a receptor for C3a are
termed C1q-R (C1q receptor), C5a-R (C5a receptor), C3a-R
(C3a receptor), and fH-R (factor H receptor).
complement system
A group of more than 30 plasma and cell surface proteins
that faciliate the destruction of pathogenic microorganisms
by phagocytes or by lysis. Refer to complement.
complementarity
A genetic term that indicates the requirement for more than
one gene to express a trait.
complementarity-determining region (CDR)
The hypervariable regions in an immunoglobulin molecule
that form the three-dimensional cavity where an epitope
binds to the antibody molecule. The heavy and light polypeptide
chains each contribute three hypervariable regions to the
antigen-binding region of the antibody molecule. Together,
they form the site for antigen binding. Likewise, the T cell
receptor α and β chains each have three regions with great
diversity that are analogous to the CDRs of the immunoglobulin.
These hypervariable areas are sites of binding for
foreign antigen and self MHC molecular complexes.
complementation
A mechanism whereby a hybrid cell develops the survival
capacity of two separate parental cells under different selective
circumstances.
complete carcinogen
A cancer-causing agent that can promote all four stages
of carcinogenesis.
complete clinical response (hematopoietic neoplasm)
Reduction to nearly zero or ≤ 5% of the number of blasts in
a post-treatment patient’s blood or bone marrow smear.
complete Freund’s adjuvant (CFA)
A suspension of killed and dried mycobacteria suspended
in lightweight mineral oil which, when combined with an
aqueous phase antigen (such as a water-in-oil emulsion),
enhances immunogenicity. CFA facilitates stimulation of
both humoral (B cell) and cell-mediated (T cell) limbs of
the immune response.
complex allotype
An allotype with multiple amino acid residue positions that are
not the same as those of a different allotype at that same locus.
complex release activity
Binding of injected preformed complexes to the endothelial
cell membranes immediately after their injection
into experimental animals. The amount of such binding
decreases with age, favoring deposition of such complexes
within tissues.
complotype
A major histocompatibility complex (MHC) class III haplotype.
It is a precise arrangement of linked alleles of MHC
class III genes that encode C2, factor B, C4A, and C4B MHC