Which receptor recognises iC3b?
Complement receptors
Complement receptors After opsonization, iC3b and C3b are recognized by different receptors: CR3 (CD11b/CD18) found on almost all phagocytes; and CR4 (CD11c/CD18) or gp150,95 found on some lymphocytes and phagocytes.
Is iC3b an Opsonin?
Although both C3b and iC3b function as opsonins, they act through different complement receptors, complement receptor 1 (CD35) and complement receptor 3 (CD11b/CD18), respectively (reviewed in reference 1).
How is C3 activated?
The C3 convertase activates C3 by cleaving the alpha chain, releasing C3a anaphylatoxin and generating C3b (beta chain + alpha’ (alpha prime) chain).
In what three ways is complement activation initiated?
There are three pathways of complement activation: the classical pathway, which is triggered directly by pathogen or indirectly by antibody binding to the pathogen surface; the MB-lectin pathway; and the alternative pathway, which also provides an amplification loop for the other two pathways.
What is the role of iC3b?
iC3b is a protein fragment that is part of the complement system, a component of the vertebrate immune system. iC3b is produced when complement factor I cleaves C3b. Complement receptors on white blood cells are able to bind iC3b, so iC3b functions as an opsonin.
When antibodies Opsonize a pathogen What are they doing?
Another mechanism by which antibodies can response to pathogens is known as “opsonization.” By opsonization, antibodies enable phagocytes for ingesting and destroying the extracellular bacterium. The phagocytes recognize the Fc region of the antibodies coating the pathogen and foreign particles (Fig. 2).
What is the function of C3?
The C3 protein is essential for turning on (activating) the complement system. The presence of foreign invaders triggers the C3 protein to be cut (cleaved) into two smaller pieces. One of these pieces, called C3b, interacts with several other proteins on the surface of cells to trigger the complement system’s response.
What is iC3b complement?
How many molecular weight proteins are in iC3b?
Thus, iC3b may be a mixture of 176,000 and 174,000 molecular weight proteins. If the C3b precursor was attached to a surface, the iC3b remains on that surface. The iC3b sold by CompTech is made from fluid phase C3b and is not capable of attaching to a surface.
How does the iC3b attach to a surface?
The iC3b sold by CompTech is made from fluid phase C3b and is not capable of attaching to a surface. Surface-bound C3b and iC3b are linked to the target through a covalent bond which may be either an ester bond or an amide bond. Ester bonds are unstable resulting in the gradual release from the particle.
Can a factor I cleave a C3b precursor?
Factor I can cleave C3b in two places in the alpha chain and if both sites are cleaved a small fragment (C3f, 2,000 Da) is released. Thus, iC3b may be a mixture of 176,000 and 174,000 molecular weight proteins. If the C3b precursor was attached to a surface, the iC3b remains on that surface.
How is C3b produced in the pathway of complement?
C3b itself is produced by all three pathways of complement (Law, S.K.A. and Reid, K.B.M. (1995)) when native C3 is cleaved releasing C3a. iC3b is prepared by cleavage of C3b by factor I in the presence of factor H. Cleavage by factors H and I occurs rapidly when the C3b is free in solution and is slower when it is attached to a surface.
