The complement component with opsonin activity is
(B) C3b[?]Opsonins In Complement System:-C fragments released during the cascade reaction help in amplifying the inflammatory response.-C2 kinins are vasoactive amines and increase permeability.-C3a and C5a are anaphylatoxins (histamine releasing) and chemotactic.-C567 is chemotactic and also brings about reactive lysis.-C3b acts as opsonin.-C5-9 acts as cytotoxic.oThe process of coating a foreign particle targeting & preparing it for phagocytosis process is "Opsonization". Substances involved are opsonins. Main opsonins from complement system is C3oExamples of opsonins include:-Antibodies: IgG and IgA-Components of the complement system; C3b, C4b, and iC3b-Mannose Binding Lectin (MBL): Initiates the formation of C3b-Membrane Attack Complex (MAC): Includes C5b, C6, C7, C8 & polymeric C9oOpsonization & complement proteins:-Mainly C3b, iC3b & C4b-C3: Most abundant protein of all complementary proteins; Cleaves into C3a and C3b-C3a: Binds and activates mast cells & basophils, release histamine.-C3b: C3b is most critical component in both classical & alternative pathway. C3b attaches to bacterial surfaces for opsonization by phagocytes.[?]C3b way work:oC3b: Opsonization; Membrane Attack Complex (MAC)oOpsonization: C3b can do thioester bond. With this bond C3b bind with pathogen.oOn the other way Macrophage has two receptor CR1 and C5a receptor.oFor binding with pathogen it needs CP C5a. CP C5a bind with C5a receptor & allows CR1 to bind with C3b which attached with pathogen. This way Macrophage can perform phagocytosis by eating up the pathogen.[?]Biological Function of Complement:oBacteriolysis, cytosisoFunction of complement fragments-Opsonization: C3b, iC3b, C4b-Mediator of inflammation: C3a, C4a, C5a-Kinin: C2a, C5a-Chemotaxis: C3a, C5a, C567oC-dependent virolysisoClean up 1C: Interfere with formation of 1C, IC-C3b-CRI-RBC.oImmunological Regulation: C3, CR1, CR2, C3b-The first step in the alternative pathway is the binding of C3b to an activator.-C3b is continuously generated in small quantities in the circulation but in the free state it is rapidly inactivated by the serum protein factors H & I.-Bound C3b is protected is such inactivation and interacts with a serum protein called factor B (C3 proactivator) to form a magnesium dependent complex 'C3b, B'
C3a
C3b
C5a
C5b
Immunology