PE anti-complement C3b/iC3b Antibody anti-C3b/iC3b - 3E7/C3b,BioLegend,846104

Complement C3 is a 185 kD glycoprotein composed of two chains linked by a disulfide bond. It is the fourth complement component to react in the classical pathway. It is also a key protein in both the alternative and the lectin complement activation pathways. C3b is proteolytically generated from C3 by cleavage of the C3a-C3b peptide bond in the protein by C3 convertase. C3b can bind covalently, via its reactive thioester, to cell surface carbohydrates or immune aggregates. Macrophages and neutrophils recognize C3b by the complement receptor 1 (CR1, CD35). Opsonization of target surfaces with C3b is central to all three pathways of complement activation. The proteolytically inactive forms of C3b, iC3b, are generated by cleavage of the alpha chain at one or two positions by factor I in the presence of co-factors, such as factor H.  A fragment of C3b, C3f, with a molecular weight of approximately 2 kD is generated when C3b is cleaved at two positions by factor I. Although iC3b is less active than C3b, iC3b’s interactions with lymphoid and phagocytic cells via CR2 (CD21) and CR3 (CD11b/CD18) can expand target-specific B and T cells. iC3b can be cleaved to form C3c and C3dg.