Untitled - D Ank Unlimited

C3 nephritic factor (C3NeF) 125 C3dg
are one half normal in heterozygotes are apparently sufficient
to avoid the clinical consequences induced by a lack
of C3 in the serum.
C3 nephritic factor (C3NeF)
An immunoglobulin G (IgG) autoantibody to the alternate
complement pathway C3 convertase that mimics the action
of properdin. C3NeF is present in the sera of patients with
membranoproliferative glomerulonephritis type II (dense
deposit disease). It stabilizes the alternate pathway C3
convertase, thereby enhancing the breakdown of C3, and
produces hypocomplementemia. Rarely, C3NeF may be IgG
autoantibodies to C3 convertase (C4b2a) of the classical
pathway. Patients with systemic lupus erythematosus (SLE)
may contain antibodies against C4b2a which stabilize the
classical pathway C3 convertase, leading to increased in
vivo cleavage of C3.
C3 PA (C3 proactivator)
An earlier designation for factor B.
(H 2 O)
C3
iC3
B
iC3B
Mg ++
iC3Bb
C3 tickover mechanism.
C3b
C3 tickover
Alternative pathway C3 convertase perpetually generates C3b.
C3 internal thioester bond hydrolysis is the initiating event.
C3a
A low molecular weight (9-kDa) peptide fragment of
complement component C3. It is comprised of the 77 N
terminal end residues of the C3 α chain. This biologically
active anaphylatoxin that induces histamine release from
mast cells and causes smooth muscle contraction is produced
by the cleavage of C3 by either classical pathway C3
convertase (i.e., C4b2a) or alternative complement pathway
C3 convertase (i.e., C3bBb). Anaphylatoxin inactivator, a
carboxyl peptidase N, can inactivate C3a by digesting the C
terminal arginine of C3a.
C3a receptor (C3a-R)
A protein on the surface membranesof mast cells and basophils.
It serves as a C3a anaphylatoxin receptor.
C3a/C4a receptor (C3a/C4a-R)
C3a and C4a share a common receptor on mast cells. When
a C terminal arginine is removed from C3a and C4a by
serum carboxyl peptidase N (SCPN), these anaphylatoxins
lose their ability to activate cellular responses. Thus,
C3a des Arg and C4a des Arg lose their ability to induce spasmogenic
responses. C3a-R has been demonstrated on guinea
pig platelets. Eosinophils have been found to bind C3a.
C3b
The principal fragment produced when complement component
C3 is split by either classical or alternative pathway
convertases (i.e., C4b2a or C3bBb, respectively). It results
D
C3
C3a
(Complement split
products in an
inflammatory
response)
RBC
Sheep RBC
with attached
hemolysin
Patient serum
heated to 56°C
No antibody
C
RBC
C
+ Unbound
complement
LYSIS
Negative reaction
Complement
C
+ +
Antigen
Antibody present
NO LYSIS
Positive reaction
All
complement
consumed
from C3 convertase digestion of the α chain of C3. It is an
active fragment, as revealed by its combination with factor
B to produce C3bBb, the alternative pathway C3 convertase.
Classical complement pathway C5 convertase is produced
when C3b combines with C4b2a to yield C4b2a3b. Factor I
splits the arginine–serine bonds in C3b, if factor H is present,
to yield C3bi. This produces the C3f peptide. Particlebound
C3b interacts with complement receptor 1. C3b
interacts with C3b receptors on macrophages, B lymphocytes,
polymorphonuclear neutrophils (PMNs), and possibly
T cells. It promotes phagocytosis and immune adherence
and may function as an opsonin.
C3b inactivator
Refer to factor I.
C3b receptor
Refer to complement receptor 1 (CR1).
C3bi (iC3b)
The principal molecular product when factor I cleaves C3b.
If complement receptor 1 or factor H is present, factor I can
split the arginine–glutamic acid bond of C3bi at position
954–955 to yield C3c and C3dg. C3bi attached to particles
promotes phagocytosis when combined with complement
receptor 3 on the surfaces of polymorphonuclear neutrophils
(PMNs) and monocytes. It also promotes phagocytosis
by binding to conglutinin in the sera of cows.
C3c
The principal molecule that results from factor I cleavage
of C3bi when factor H or complement receptor 1 is present.
C3c is comprised of 27- and 43-kDa α chain fragments
linked through disulfide bonds to a whole β chain.
C3d
A 33-kDa B cell growth factor formed by proteolytic
enzyme splitting of a lysine–histidine bond in C3dg at position
1001–1002. C3d is comprised of the carboxyl terminal
301-amino acid residues of C3dg. It interacts with complement
receptor 2 on the surfaces of B cells. C3d contains the
C3 α chain thioester.
C3dg
A 41-kDa, 349-amino acid residue molecule formed by the
cleavage of C3bi, with factor H or complement receptor 1
present. Polymorphonuclear neutrophil leukocytes express
complement receptor 4, which is reactive with C3dg.
Complement receptor 2 on B cells is also a C3dg receptor.
Ab
C
RBC
Complement fixation.
Complement
RBC
C