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Complements are words or groups of words that are necessary to complete the meaning of another part of the sentence. Complements act like modifiers to add additional meaning to the word or words they are attached to. However, unlike adjunct modifiers, they do not add supplemental information—they provide information that is necessary to achieve the intended meaning in the sentence.
Complements, even those that complete the meaning of the subject, are always part of the predicate.
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see immunityimmunity,
ability of an organism to resist disease by identifying and destroying foreign substances or organisms. Although all animals have some immune capabilities, little is known about nonmammalian immunity.
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A group of proteins in the blood and body fluids that play an important role in humoral immunity and the generation of inflammation. When activated by antigen-antibody complexes, or by other agents such as proteolytic enzymes (for example, plasmin), complement kills bacteria and other microorganisms. In addition, complement activation results in the release of peptides that enhance vascular permeability, release histamine, and attract white blood cells (chemotaxis). The binding of complement to target cells also enhances their phagocytosis by white blood cells. The most important step in complement system function is the activation of the third component of complement (C3), which is the most abundant of these proteins in the blood.

Genetic deficiencies of certain complement subcomponents have been found in humans, rabbits, guinea pigs, and mice. Certain deficiencies lead to immune-complex diseases, such as systemic lupus erythematosus; other deficiencies result in increased susceptibility to bacterial infections, particularly those of the genus Neisseria (for example, gonorrhea and meningococcal meningitis), and hereditary angioneurotic edema. See Complement-fixation test, Immunity



a protein complex found in fresh blood serum; an important factor in natural immunity in animals and man. The term was introduced in 1899 by the German scientists P. Ehrlich and J. Morgenroth.

Complement consists of nine components, designated C’1 to C’9. The first component includes three subunits. All 11 proteins in complement may be isolated by immunochemical and physicochemical methods. Complement decomposes readily when serum is heated, stored for a long time, or exposed to light.

Complement participates in a number of immunological reactions. Attaching itself to an antigen-antibody complex on the surface of the cell membrane, it produces the lysis of bacteria, erythrocytes, and other cells that have been treated with the appropriate antibodies. All nine components of complement are required for the destruction of the membrane and the subsequent lysis of the cell. Some components of complement have enzymic activity; a component that attaches itself to the antigen-antibody complex catalyzes the attachment of the next component. In the body, complement also participates in antigen-antibody reactions that do not lead to cell lysis. The body’s resistance to pathogenic microbes, the release of histamine in allergic reactions of the immediate type, and autoimmune processes are all connected with the action of complement. In medicine, preserved preparations of complement are used in the serological diagnosis of a number of infectious diseases and in the detection of antigens and antibodies.


Reznikova, L. S. Komplement i ego znachenievimmunologicheskikhreaktsiiakh. Moscow, 1967.
Complement. Edited by G. E. W. Wolstenholme and J. Knight. London, 1965.
Müller-Eberhard, H. J. “Chemistry and Reaction Mechanisms of Complement.” Advances in Immunology,1968, vol. 8.



A heat-sensitive, complex system in fresh human and other sera which, in combination with antibodies, is important in the host defense mechanism against invading microorganisms.
The complement of a number A is another number B such that the sum A + B will produce a specified result.
For a subset of a set, the collection of all members of the set which are not in the given subset.
For a fuzzy set A with membership function mA, the complement of A is the fuzzy set Ā whose membership function m Ā has the value 1 -mA (x) for every element x.
The complement of a simple graph, G, is the graph, G with the same vertices as G, in which there is an edge between two vertices if and only if there is no edge between those vertices in G.
The complement of an angle A is another angle B such that the sum A + B equals 90°.


1. the officers and crew needed to man a ship
2. Maths the angle that when added to a specified angle produces a right angle
3. Logic Maths the class of all things, or of all members of a given universe of discourse, that are not members of a given set
4. Music the inverted form of an interval that, when added to the interval, completes the octave


The other value or values in the set of possible values.

See logical complement, bitwise complement, set complement.


The number derived by subtracting a number from a base number. For example, the tens complement of 8 is 2. In set theory, complement refers to all the objects in one set that are not in another set.

Complements are used in digital circuits, because it is faster to subtract by adding complements than by performing true subtraction. The binary complement of a number is created by reversing all bits and adding 1. The carry from the high-order position is eliminated. The following example subtracts 5 from 8.

Decimal    Binary    Complement
      8          1000      1000
     -5         -0101     +1011
     __         _____     _____
      3          0011      0011