Microbiology and Immunology

Adjuvant WORLD OF MICROBIOLOGY AND IMMUNOLOGY

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rodents. This was the first known human virus capable of

inducing tumors in animals.

More recently, the basis of the tumor-inducing activity

has been unraveled. Genes that are active early in the replica-

tion cycle of adenovirus produce proteins that interfere with

host proteins that are known as anti-oncogenes. Normally, the

anti-oncogen proteins are responsive to cell growth, and so act

as a signal to the cell to halt growth. By disrupting the anti-

oncogene proteins, this stop signal is eliminated, resulting in

the continued and uncontrolled growth of the cell. A tumor is

produced. Thus, adenoviruses have become important as one

of the central triggers of cancer development.

Such cancers may be a by-product of adenovirus infec-

tions. These infections are not by themselves serious. Most

tend to appear and run their course within a few weeks. The

infections are fairly common. For example, most children will

have antibodies to at least four types of adenovirus.

Adenovirus gains entry through a break in the skin or are

inhaled. The stick-and-ball appearing penton fibers may have

a role in the attachment of the virus particle to a protein on the

surface of the host epithelial cell.

Adenovirus infections have contributed to the spread of

bacterial antibiotic resistancebecause of the overuse of

antibiotics. The flu-like symptoms of some adenovirus infec-

tions can lead to the prescribing of antibiotics as a treatment.

However, antibiotics are ineffective against viruses. But the

circulating antibiotic can provide selective pressure on the

development of resistant in bacterial populations.

See alsoBacterial adaptation; Transformation

AAdjuvantDJUVANT

An adjuvant is any substance that enhances the response of the

immune systemto the foreign material termed an antigen. The

particular antigen is also referred to as an immunogen. An

adjuvant can also be any substance that enhances the effect of

a drug on the body.

When antigen is injected into an organism being used to

raise antibodies the effect is to stimulate a greater and more

prolonged production of antibodythan would otherwise occur

if the antigen were injected alone. Indeed, adjuvants are very

useful if a substance itself is not strongly recognized by the

immune system. An example of such a weak immunogen is

the capsule exopolysaccharide of a variety of bacteria.

Adjuvants exert their effect in several different ways.

Firstly, some adjuvants retain the antigen and so “present” the

antigen to the immune system over a prolonged period of time.

The immune response does not occur all at once, but rather is

Negative stain electron micrograph of an Adenovirus.

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