Immunology: Complememt system and its types, Mechanism

The document discusses the three pathways of the complement system - the classical pathway, alternative pathway, and lectin pathway. The classical pathway is activated by antigen-antibody complexes and involves C1, C4, C2, and C3. The alternative pathway involves spontaneous activation of C3 and forms the C3 convertase C3bBb. The lectin pathway is activated upon recognition of mannose residues on microbial surfaces by mannose-binding lectin or ficolins, activating MASPs and forming the C3 convertase C4bC2a.