C3/C3b, Human, mAb 755

The monoclonal antibody 755 recognizes an epitope located in the C-terminal 360 amino acids-on the alpha chain of C3, thereby recognizing C3b and full C3. The complement system is an important factor in innate immunity. The third complement component, C3, is central to the classical, alternative and lectin pathways of complement activation. The synthesis of C3 is tissue-specific and is modulated in response to a variety of stimulatory agents. C3 is the most abundant protein of the complement system with serum protein levels of about 1.3 mg/ml. An inherited deficiency of C3 predisposes a person to frequent bacterial infections. C3 fragments are deposited in tissues at sites of antibody-mediated immunopathology. In ulcerative colitis and idiopathic chronic inflammatory bowel disease, the deposition of C3 in the diseased mucosa has been reported. After activation of the complement system, certain enzymes become active, resulting in the cleavage of C3 into C3b and the anaphylatoxin C3a. C3b becomes attached to immune complexes and is further cleaved into iC3b, C3c, C3dg and C3f. Within the alternative pathway of complement, C3b plays a critical role in the amplification loop initiated by spontaneous hydrolysis of C3.