Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Complement

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formed on surfaces under water that attracted oyster larvae to

settle and grow.

In the spirit of using knowledge gained from the sea to

benefit humans and the environment, Colwell prepared a

seminal paper on marine biotechnology published in the jour-

nal Sciencein 1983. It brought attention to the rich resources

of the ocean that might be tapped for food, disease-curing

drugs, and environmental clean-up by the applications of

genetic engineering and cloning. In order to realize the poten-

tial of marine biotechnology as originally outlined in her

1983 paper, Colwell helped foster the concept and growth of

the University of Maryland Biotechnology Institute, estab-

lished in 1987. As president of the U.M.B.I., she has formed

alliances between researchers and industry and has succeeded

in raising funds to develop the center as a prestigious biotech

research complex.

In addition, Colwell has held numerous professional

and academic leadership positions throughout her career and

is a widely published researcher. At the University of

Maryland, Colwell was director of the Sea Grant College from

1977 to 1983. She served as president of Sigma Xi, the

American Society for Microbiology, and the International

Congress of Systematic and Evolutionary Biology, and was

president-elect of the American Association for the

Advancement of Science. Colwell has written and edited more

than sixteen books and over four hundred papers and articles.

She also produced an award-winning film, Invisible Seas. Her

honors included the 1985 Fisher Award of the American

Society for Microbiology, the 1990 Gold Medal Award of the

International Institute of Biotechnology, and the 1993 Phi

Kappa Phi National Scholar Award.

Colwell is the mother of two daughters who pursued

careers in science. She is an advocate for equal rights for

women, and one of her long-standing aspirations is to write a

novel about a woman scientist. Her hobbies include jogging

and competitive sailing.

See alsoBioremediation; E. coliO157:H7 infection; Eco-

nomic uses and benefits of microorganisms; Water purifi-

cation

COMBINED IMMUNODEFICIENCY •see

IMMUNODEFICIENCY DISEASE SYNDROMES

COMMERCIAL USES OF MICROORGANISMS

• seeECONOMIC USES AND BENEFITS OF MICROORGANISMS

COMMON VARIABLE IMMUNODEFICIENCY

DISEASE(CVID)• seeIMMUNODEFICIENCY DISEASE

SYNDROMES

COMPETITIVE EXCLUSION OF BACTERIAL

ADHESION• seeANTI-ADHESION METHODS

CComplementOMPLEMENT

Complement refers to a series of some 30 proteins that enhance

the bacterial killing effect of antibodies. This complementation

involves facilitating the engulfing of bacteriaby immune cells

in the process known as phagocytosis, or by the puncturing of

the bacterial membrane. Additionally, complement helps dis-

pose of antigen-antibody complexes that form in the body.

The various complement proteins circulate throughout

the bloodstream in an inactive form. When one of the pro-

teins is converted to an active form upon interaction with an

antigen-antibody complex, a series of reactions is triggered.

The activation step involves the cleaving, or precise cutting,

of the particular complement protein. The cleavage turns the

complement protein into a protease, a protein that is itself

capable of cleaving other proteins. In turn, cleavage of a sec-

ond complement protein makes that protein a protease. The

resulting cleavage reaction generates a series of active com-

plement proteins. These reactions, known as the complement

cascade, occur in an orderly sequence and are under precise

regulation.

The reactions involve two pathways. One is known as

the classical complement activation pathway. The end result is

an enzyme that can degrade a protein called C3. The other

pathway is known as the alternative pathway. The second

pathway does not require the presence of antibodyfor the acti-

vation of complement. Both pathways result in the formation

of an entity that is called the membrane attack complex. The

complex is actually a channel that forms in the bacterial mem-

brane. Under the magnification of the electron microscope, a

bacterial membrane that is a target of the complement system

appears riddled with holes.

The channels that form in a membrane allow the free

entry and exit of fluids and molecules. Because the concentra-

tion of various ions is higher inside the bacterium than outside,

fluid will flow inward to attempt to balance the concentra-

tions. As a result, the bacterium swells and bursts.

Other reaction products of the complement cascade

trigger an inflammatory immune response. In addition, the

invading bacteria are coated with an immune molecule (C3b)

that makes the bacteria more recognizable to phagocytes. This

process is called opsonization. The phagocytes then engulf the

bacteria and degrade them.

Tight control over the activity of the complement system

is essential. At least 12 proteins are involved in the regulation

of complement activation. Defects in this control, or the oper-

ation of the pathways, result in frequent bacterial infections.

See alsoImmune system; Infection and control

COMPLEMENT DEFICIENCY•see

IMMUNODEFICIENCY DISEASE SYNDROMES

COMPLETED TESTS•seeLABORATORY TECHNIQUES

IN MICROBIOLOGY

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