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(prō`pərdən), protein found in the blood serum of humans and some of the higher animals that appears to participate in certain specific immune responses. It is associated with the engulfing of foreign particles and invading cells by phagocytes and with tissue inflammation (see bloodblood,
fluid pumped by the heart that circulates throughout the body via the arteries, veins, and capillaries (see circulatory system; heart). An adult male of average size normally has about 6 quarts (5.6 liters) of blood.
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; 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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). Properdin has been isolated in highly purified form.



in mammals, a protein in blood serum, one of the globulins and one of the factors of natural immunity. Properdin participates in destroying bacteria and protozoans, neutralizing viruses, and stimulating phagocytosis either independently or by activating the complement system.

In man, properdin is a homogeneous protein detected electrophoretically in the beta-globulin region; its molecular weight is 223,000. In a healthy person, 1 milliliter of blood contains 2.5—8 micrograms of properdin nitrogen. Properdin content decreases with burns, after irradiation, and with malignant neoplasms; it increases with the introduction of bacterial endotoxins.

Properdin differs functionally and antigenetically from immunoglobulins and complement factors. It is a part of the properdin system, a special system of serum proteins that function together; the system was discovered in 1954 by the American scientist L. Pillemer and his colleagues. The properdin system includes properdin, factor A (a protein inactivated by hydrazine), factor B (a β-glycoprotein with an increased content of glycine), and an Mg2+ ion.


Chernokhvostova, E. V. “Sistema properdina.” In L. S. Reznikova, Komplement i ego znachenie v immunologicheskikh reaktsiiakh. Moscow, 1967. Pages 157–84.
“Properties of Highly Purified Human Properdin.” Journal of Immunology, 1968, vol. 100, no. 1.



A macroglobin of normal plasma capable of killing various bacteria and viruses in the presence of complement and magnesium ions.
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