Question

Describe in detail the complement system (Classical, alternative and Lectin/Mannan pathway); include opsonization, MAC and inflammation.

Answer 1

Answer:

Complement system - Complement components comprise of protein and glycoprotein produced by monocytes, hepatocyte macrophages and epithelial cells of the intestinal deas. tract. - These components are designated by numerals as ci-ca, also by the Letter symbols Active fragments of complement component is designatod by drall letters: smallerfragment of the cleaved component is designated as ca" and the larger fragment as ab

Activities of complement system affect both innate and acquired immunity, These components after activation intracts in a cascade to carry out the basic functions related to our simunity je enhances the ability of antibodies and phagocytic cells, promotes inflamma- - tion .

Activation of complement occurs by the three pathways classical, alternative or lectin. These three pathways converge in a common sequence of events that causes cell lysis which triggered by different mechanism.

• The classical pathway begins with the formation of antigen-antibody complexes or with the binding of antibody to antigen and is triggered by the activation of the C1 complex. The initial stage of activation involves components C1, C2, C3, and C4, present as inactive forms in plasma.
• Activation of the alternative and lectin pathways is antibody-independent.

The alternative pathway is initiated by binding of C3b to activating surfaces such as microbial cell walls.

• The lectin pathway is initiated by binding of the serum protein MBL (Mannose binding lectin) to the surface of microorganisms.

Cleavage of C3 is the major amplification step. The three pathways of complement system generate C3 convertase and C5 convertase.

Clasical pathway Alternative pathway Lectin pathway Activators Formation of antigen- antibody complex Activating surfaces microbial cell walls Mannose and N-acetylglucosamine containing bacterial cell wall W 100 Initiation Clq binding to Ab-Ag complex Deposition of C3b onto activated surfaces * MBL binding to bac. cell wall Cascade This complex cleaves C2 and C4 This complex cleaves C2 and C4 to form C4b2a complex (C3 convertase) C3b binds factor B that is cleaved by factor D to form C3 convertase AL 101 C3a + C3b C3b initiates C3a initiates inflammation initiate classic pathway Jopsonisation C5---> Cha C5b--> C6-->C7-->08--> C9 Anaphylaxation Lysis by MAC (membrane attack complex) formation