Concept
Complement system
Cascade of opsonization, inflammation, and lysis
High-yield clue
All three pathways converge on C3, and C5b-C9 assemble the membrane attack complex (MAC) that lyses cells.
Overview
A cascade of serum proteins that enhances host defense through three activation pathways (classical, lectin/MBL, and alternative) converging on C3. It bridges innate and adaptive immunity and is a frequent exam topic.
Classification
- Immunology concept
- Three activation pathways
- Enzyme cascade of serum proteins
Lab & identification clues
- C3b is the major opsonin (tags microbes for phagocytosis)
- C3a and C5a are anaphylatoxins; C5a is a chemoattractant
- MAC (C5b-C9) causes membrane lysis, key against Neisseria
Associations
- Terminal complement deficiency and Neisseria susceptibility vocabulary
- Encapsulated organisms evade complement/opsonization
- Classical pathway triggered by antibody-antigen complexes
Commonly confused with
- Classical vs alternative pathway triggers
- Opsonization vs MAC lysis
Frequently asked questions
What is Complement system?
A cascade of serum proteins that enhances host defense through three activation pathways (classical, lectin/MBL, and alternative) converging on C3. It bridges innate and adaptive immunity and is a frequent exam topic.
What is the high-yield clue for Complement system?
All three pathways converge on C3, and C5b-C9 assemble the membrane attack complex (MAC) that lyses cells.
What is Complement system associated with?
Complement system is associated with Terminal complement deficiency and Neisseria susceptibility vocabulary, Encapsulated organisms evade complement/opsonization, and Classical pathway triggered by antibody-antigen complexes.
What is Complement system commonly confused with?
Complement system is commonly confused with Classical vs alternative pathway triggers and Opsonization vs MAC lysis.
Original microbiology concept summary. Sources checked: OpenStax Microbiology 2e, NCBI Bookshelf Medical Microbiology, and CDC/WHO topic pages where applicable; reviewed 2026-06. Educational only; no diagnosis, treatment selection, infection-control instructions, or specimen-handling guidance.