C3b Rabbit

Complement C3b is derived from the cleavage of complement component 3 (C3). C3 is central to the activation of all three pathways of complement activation: the classical pathway, the lectin pathway, and the alternative pathway. The cleavage of C3 by C3 convertase enzymes results in the formation of two fragments: C3a and C3b. C3a is an anaphylatoxin, while C3b is a larger fragment that plays a pivotal role in opsonization and the formation of the membrane attack complex (MAC).

The primary function of C3b is to act as an opsonin. Opsonization is the process by which pathogens are marked for ingestion and elimination by phagocytes. C3b achieves this by covalently binding to the surface of pathogens. This binding is facilitated by a thioester bond that is exposed upon the cleavage of C3. The thioester bond allows C3b to attach to hydroxyl groups on the pathogen’s surface, which can be found on carbohydrates, proteins, and other molecules.

Once bound to the pathogen, C3b interacts with complement receptors on phagocytic cells, such as macrophages and neutrophils, enhancing their ability to recognize and engulf the pathogen. This process is crucial for the clearance of pathogens and immune complexes from the bloodstream and tissues.

The activity of C3b is tightly regulated to prevent damage to host tissues. Regulatory proteins, such as factor H and factor I, inactivate C3b by cleaving it into smaller fragments, such as iC3b. These fragments still retain some opsonic activity but are less potent than intact C3b. This regulation ensures that the complement system targets only pathogens and not the host’s own cells.

Dysregulation of the complement system, including the activity of C3b, can lead to various diseases. For example, excessive activation of the complement system can contribute to inflammatory diseases, such as autoimmune disorders and chronic inflammatory conditions. Conversely, insufficient complement activity can result in increased susceptibility to infections.

Rabbit C3b is often used in research to study the complement system and its role in immune responses. It is derived from purified rabbit C3 and is used in various experimental setups to investigate the mechanisms of complement activation, regulation, and its effects on pathogens and host cells .