Immunology Complement System

Ali is a 4 year old boy which is infected by a certain microbe. He has a fever, malaise and cough, earlier symptoms that indicates he is in the initial phase of his disease attack.This is because his body defense mechanism is fighting against antigen. From the signs shown, he is believed to have lung infection. His body immune system is activated to protect Ali. The first type of the immune system that acts to protect Ali is innate immune system which provides immediateresponse towards the infection to protect the body against the microbe. Innate immune system acts in a generic way to all infection with no adaptation and does not confer long-lasting immunity. One of the componentsof innate immune system is complement system which is major part of it.In case of Ali; the infection first triggered the complement system.

The complement system.

The complement system is an enzyme cascade that helps defend against infection.We know that in complement system, alternative pathway and mannose-binding lectin are activated first followed by the classical pathway. Next, we are going to explain about the classical pathway, mannose-binding lectin, and alternative pathway which are the component of complement system. All these pathways lead to the formation of C3 convertase that cleaves C3 to C3a and C3b.

Classical pathway.

Classical pathway is activated when antibodies bound to antigens on cells surface. Protein that involved in classical pathway is C1 which consist of C1q,2 C1r,2 C1s. Antibody binding is mediated by much larger portion of the complex, C1q which binds the Fc portion of immunoglobulin. Binding of C1q activates C1s and C1r. Activated C1s will split both C4 and C2. The small fragments, C4a and C2b, are lost and major components form C4b2a. The complex of C4b2a is called C3 convertase as it catalyses the cleavage of C3. C3 convertase will cut C3 into two major fragments, C3a and