Summary
A cascade of blood proteins that punches holes in microbes and enhances phagocytosis.
In depth
More than 30 proteins activated by classical (antibody), alternative (microbial surfaces) and lectin pathways. C3b opsonises, C5a recruits phagocytes, and the membrane attack complex forms pores. Regulators protect host cells.
Complement ties innate and adaptive immunity because antibodies activate the classical pathway. Deficiencies cause infections or autoimmunity.
Example: hereditary angioedema results from missing C1 inhibitor.
Frequently asked questions
What is Complement System?
A cascade of blood proteins that punches holes in microbes and enhances phagocytosis.
Which area of biology covers Complement System, and how advanced is it?
Complement System is one of the 52 topics in Immunology & Disease. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include Innate Immunity, Immune System, Phagocytosis.
Can you give an example of Complement System?
People lacking late complement components get recurrent Neisseria infections.
What should I learn before Complement System?
Work through the Beginner topics in Immunology & Disease first, such as Immune System, Viruses, Innate Immunity, then return to Complement System. Intermediate topics assume the Beginner vocabulary.
What topics are related to Complement System?
The closest topics to Complement System are Innate Immunity, Immune System, Phagocytosis, Natural Killer Cells. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Complement System?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Complement System. To practise the whole of Immunology & Disease, use the Immunology & Disease quiz.
How is Complement System different from Innate Immunity?
Complement System: A cascade of blood proteins that punches holes in microbes and enhances phagocytosis. Innate Immunity: Rapid, non-specific defences such as skin, mucus, phagocytes and inflammation. Read both side by side and note what each one explains.
How should I study Complement System step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Innate Immunity and explain the difference aloud. Finally, take the Immunology & Disease quiz and come back to this page for any question you miss.