C3bmolekyyli

C3bmolekyyli, a fragment of the third complement protein C3, plays a crucial role in the immune system's complement cascade. When the complement system is activated, C3 undergoes cleavage, yielding C3a and C3b. C3b is the larger and more biologically active fragment. Its primary function is to act as an opsonin, a molecule that coats pathogens and marks them for phagocytosis by immune cells such as macrophages and neutrophils. This process, known as opsonization, significantly enhances the efficiency of pathogen clearance.

Beyond opsonization, C3b is central to the amplification of the complement cascade. It can bind to other complement proteins, initiating the formation of the C5 convertase enzyme. This enzyme then cleaves C5, leading to the generation of C5a and C5b. C5b initiates the formation of the membrane attack complex (MAC), which can lyse target cells. C3b also plays a role in the classical and lectin pathways of complement activation by binding to antibody-antigen complexes or microbial carbohydrates, respectively. Dysregulation of C3b production or function can lead to various immune disorders, highlighting its importance in maintaining immune homeostasis.