complement

—complementer, n.

n. /kom"pleuh meuhnt/; v. /kom"pleuh ment'/, n.

1. something that completes or makes perfect: A good wine is a complement to a good meal.

2. the quantity or amount that completes anything: We now have a full complement of packers.

3. either of two parts or things needed to complete the whole; counterpart.

4. full quantity or amount; complete allowance.

5. the full number of officers and crew required on a ship.

6. Gram.

a. a word or group of words that completes a grammatical construction in the predicate and that describes or is identified with the subject or object, as small in The house is small or president in They elected her president. Cf. object complement, subject complement.

b. any word or group of words used to complete a grammatical construction, esp. in the predicate, including adverbials, as on the table in He put it on the table, infinitives, as to go in They are ready to go, and sometimes objects, as ball in He caught the ball.

7. Geom. the quantity by which an angle or an arc falls short of 90° or a quarter of a circle. Cf. supplement (def. 4).

8. Also called absolute complement. Math. the set of all the elements of a universal set not included in a given set.

9. Music. the interval that completes an octave when added to a given interval.

10. Immunol.

a. a system in vertebrate blood of 12 or more proteins that react in a cascade to a cell displaying immune complexes or foreign surfaces, acting in various combinations to coat the cell and promote phagocytosis, make holes in the cell wall, or enhance the inflammatory response.

b. any of the proteins in the complement system, designated C1, C2, etc.

11. See complementary color.

v.t.

12. to complete; form a complement to: This belt complements the dress better than that one.

13. Obs. to compliment.

v.i.

14. Obs. to compliment.

[1350-1400; ME < L complementum something that completes, equiv. to comple(re) to fill up (see COMPLETE) + -mentum -MENT]

Syn. 12. COMPLEMENT, SUPPLEMENT both mean to make additions to something. To COMPLEMENT is to provide something felt to be lacking or needed; it is often applied to putting together two things, each of which supplies what is lacking in the other, to make a complete whole: Two statements from different points of view may complement each other. To SUPPLEMENT is merely to add to: Some additional remarks may supplement his address.

Usage. COMPLEMENT and COMPLIMENT, which are pronounced alike and originally shared some meanings, have become separate words with entirely different meanings. As a noun, COMPLEMENT means "something that completes or makes perfect": The rare old brandy was a perfect complement to the delicious meal. As a verb, COMPLEMENT means "to complete": A bright scarf complements a dark suit. The noun COMPLIMENT means "an expression of praise, commendation, or admiration": The members paid her the compliment of a standing ovation. The verb COMPLIMENT means "to pay a compliment to": Everyone complimented him after the recital.

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In physiology, a complex system of at least 20 proteins (complement components) in normal blood serum.

The binding of one component to an antigen-antibody complex begins a chemical chain reaction important in many immunological processes, including breakdown of foreign and infected cells, ingestion of foreign particles and cell debris, and inflammation of surrounding tissue. Complement components and antibodies are the substances in human serum responsible for killing bacteria.

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▪ immune system component

      in immunology, a complex system of more than 30 proteins that act in concert to help eliminate infectious microorganisms. Specifically, the complement system causes the lysis (bursting) of foreign and infected cells, the phagocytosis (ingestion) of foreign particles and cell debris, and the inflammation of surrounding tissue.

      The interacting proteins of the complement system, which are produced mainly by the liver, circulate in the blood and extracellular fluid, primarily in an inactivated state. Not until the system receives an appropriate signal are they activated. The signal sets off a chemical chain reaction in which one activated complement protein triggers the activation of the next complement protein in the sequence.

 Complement activation occurs by two routes, called the classical pathway and the alternative pathway, or properdin system. A different type of signal activates each pathway. The classical pathway is triggered by groups of antibodies (antibody) bound to the surfaces of a microorganism, while the alternative pathway is spurred into action by molecules embedded in the surface membranes of invading microorganisms and does not require the presence of antibodies. Both pathways converge to activate the pivotal protein of the complement system, called C3.

      The activation of C3 fragments the protein into two pieces—a smaller piece, called C3a, which promotes an inflammatory reaction, and a larger piece, called C3b, which binds to the surface of a microbial cell. C3b helps bring about the elimination of the microbial invader in two ways:

● Bound C3b activates the formation of membrane attack complexes, structures composed of other complement proteins that poke holes into the membrane of the invading microorganism and allow the contents of the cell to leak out and the cell to die.

● The C3b-coated microorganism attracts white blood cells called macrophages and neutrophils and enhances their ability to ingest the microorganism or transport it to the liver or spleen for further processing.

      Complement was identified in the late 19th century as one of two soluble proteins in human blood serum responsible for killing bacteria, the other substance being antibody. The original complement protein was called alexin, but its name was eventually changed to indicate how the protein “complemented” the action of antibody in carrying out bacterial lysis. The classical pathway was characterized in the early part of the 20th century, prior to the discovery of the alternative pathway, which was described in the 1940s but not fully appreciated until the 1970s. Because antibodies are not needed to activate the alternative pathway—but are required to set off the classical cascade—the alternative pathway serves as a first defense against infection and is part of the nonspecific, innate immune response, which occurs before a specific, acquired immune response can be mounted. The alternative pathway appears to be the more primitive of the two systems, and the nomenclature, therefore, indicates the sequence of discovery of the two pathways and not their evolutionary history.

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