Complement system

[Marquetta]

The complement system is an enzyme cascade that helps defend against infection. Many complement proteins occur in serum as inactive enzyme precursors (zymogens); others reside on cell surfaces. (See also Overview of the Immune System.)
The complement system bridges innate and acquired immunity by

Augmenting antibody (Ab) responses and immunologic memory
Lysing foreign cells
Clearing immune complexes and apoptotic cells

Complement components have many biologic functions (eg, stimulation of chemotaxis, triggering of mast cell degranulation independent of immunoglobulin E [IgE]).

[Tracie Lynn]

a group of proteins that works with other substances as part of the immune system: