| Search Bloodindex | ||
|
||||
Complement SystemComplement SystemComplement is a protein complex composed of alpha and beta globulins which play an important part in antigen-antibody reactions. It is found in all human sera and is destroyed by exposure to heat. Complement system is a group of about 20 distinct serum proteins which in response to a stimulus interact with each other, antibody and the cell membrane. The complement is involved in biological effects such as immune adherence, phagocytosis and cell lysis. The activity of complement depends on nine serum protein components (C1-C9) which are present in blood circulation as functionally inactive molecules and comprise 4-5% of toal serum proteins. Complement proteins are designated by C, followed by identification number and letters. Activation of complement may be by the classical pathway or the alternate pathway. Classicial pathway Cl- C9 Alternate pathway C3,C3b, Factor B, D,f-l,l,C5-C9 Activation of classical pathway --- Attachment, activation & amplification Antigen-antibody complex initiates the complement cascade. Cl consists of Clq CIr CIs components. Clq consists of 6 subunits. Clq binds to Fc portion of immunoglobulin which is complexed to its corresponding antigen. Two of the 6 subunits must bind for activation. Bound Clq activates Cir which activates CIs. Activated CIs cleaves C4 to C4a & C4b. C4b complexes with C2 to form C4b2a complexes (C3 convertase) which further activating C3 into C3a & C3b to form C4b2a3b complex (C5 convertase). This complex facilitates opsonization. A single C4b2a activates complex of hundreds of molecules of C3. C5a, C4b and C3a are released into plasma and they act as potent anaphylotoxins. C5a is chemotactic, attracts neutrophils and stimulates inflammation. C4b2a3b splits C5 into C5a & C5b. --- Attack complex C5-C9 form a complex on the cell membrane. C5b fixes to cell membrane followed by sequential addition of C6,C7 CS and C9 or membrane attack complex which is a tabular structure. This traverses the cell membrane, produces holes and results in increase membrane permeability allowing influx of Na and 1I2O and lysis of the cell. Alternate pathway It provides a mechanism for complement activation when sufficient antibody is not available e.g. in primary infection. Components of cell membrane of the micro-organisms such as polysaccharides and lipopolysaccharides initiate cleavage of C3 to C3b. C3b activates Factor B to Bb and Ba, C3bBb complex is a C3 convertase and amplifies formation of C3b. C3bBb properd- in is a C5 convertase. Subsequent steps of activation are the same.
Blood bank zone
Next Articles
You are here : Home/
Blood Bank Zone/
Principles of Immunohaematology/ 5. Complement System |
|
|
|
||
|
Events | About us | Link to us | Contact us | Associates | Services | Fund-rising options | Feedback | Privacy policy | Disclaimer | RSS feed © 2007 bloodindex |
||
