How can properdin be activated?
How can properdin be activated?
The properdin complement pathway is initiated as a result of spontaneous hydrolysis of the C3 component of complement in serum. This produces a cleavage product, C3b, that binds to microbial surfaces, forming an enzyme, C3 convertase, which initiates the activation of the subsequent complement components (Figure 12.1).
How is the alternative pathway activated?
The alternative pathway (AP) is slowly activated spontaneously by hydrolysis of the internal C3 thioester bond [12–14] and further triggered by contact with various proteins, lipids and carbohydrate structures on microorganisms and other foreign surfaces [1, 15].
What does properdin do in alternative pathway?
Properdin is a positive regulator of complement activation that stabilizes the alternative pathway convertases (C3bBb). Properdin is composed of multiple identical protein subunits, with each subunit carrying a separate ligand-binding site.
What is properdin system?
The properdin system is responsible for the bactericidal action of normal human serum against a variety of microorganisms. The present work shows that the removal of properdin from serum also removes bactericidal activity. Addition of properdin to properdin-deficient serum restores bactericidal activity.
How is classical pathway activated?
The classical pathway is normally triggered by antigen–antibody complexes that bind the C1 complex (C1q, C1r, C1s) through the C1q component. This activates C1s, which is then able to cleave the C4 complement protein into C4a and C4b.
What triggers the lectin pathway?
The lectin pathway is initiated when pattern-recognition molecules (MBL, CL-K1, and ficolins) bind to the so-called pathogen-associated molecular patterns (PAMPs) (D-mannose, N-acetyl-D-glucosamine, or acetyl groups), on the surface of pathogens or to apoptotic or necrotic cells (9).
What does factor P do?
Factor P acts as a pattern recognition molecule to bind selectively to specific surfaces upon which it recruits C3b or C3(H2O) to direct and trigger alternative pathway. Factor P can bind early apoptotic T cells, which promotes their phagocytic uptake by macrophages and dendritic cells.
What is the function of c3bbb?
C3b is the larger of two elements formed by the cleavage of complement component 3, and is considered an important part of the innate immune system. C3b is potent in opsonization: tagging pathogens, immune complexes (antigen-antibody), and apoptotic cells for phagocytosis.
What is the function of IgM?
IgM not only serves as the first line of host defense against infections but also plays an important role in immune regulation and immunological tolerance. For many years, IgM is thought to function by binding to antigen and activating complement system.