Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Avery, Oswald Theodore

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and is obtained in the same way that blood is obtained during

blood donation procedures. As well, blood can be recovered

from the umbilical cord following the birth of an infant. In

both cases, the blood is stored for future use by the individual

or for the extraction of a particular form of cell known as the

stem cell.

Blood and blood products (e.g., plasma) can be stored in

frozen form for extended periods of time without degrading.

Thus, autologous banking represents a decision by an individ-

ual to maintain his/her blood in the event of a future mishap.

One motivation for autologous blood banking can be the

increased assurance that the blood that will be used in subse-

quent operations or blood transfusions is free of contaminating

microorganisms(e.g., HIV, hepatitis, etc.). Regardless, even

with blood screening technologies there are still several hun-

dred thousand transfusion-associated cases of hepatitis in the

United States each year. From an immunological viewpoint,

another reason for autologous banking is that autologous

blood will be immunologically identical to the blood present

at the time of return transfusion. This eliminates the possibil-

ity of an immune reaction to blood that is antigenically differ-

ent from the individual’s own blood.

The autologous blood collected from the umbilical cord

is a source of stem cells. Stem cells are cells that have not yet

undergone differentiation into the myriad of cell types that

exist in the body (e.g., red blood cells, white blood cells, tis-

sue cells), and so retain the ability to differentiate. Thus,

under appropriate conditions, stem cells can be encouraged to

differentiate into whatever target cell is desired. Although this

reality has not yet been fully realized, the potential of stem

cell technology as a therapy for various diseases has been

demonstrated.

Umbilical cord blood cells also offer the advantage of

being a closer match immunologically between individuals.

The differences in blood cells between individuals due to the

so-called major histocompatibilityantigen is not as pronounced

in cord blood cells. Thus, umbilical cord blood cells and tissue

can be used for donation and transplantation. In addition, cord

blood from closely related individuals can be pooled without

inducing an immune response upon the use of the blood.

See alsoAntibody and antigen; Histocompatibility; Immunity,

cell mediated

AAutotrophic bacteriaUTOTROPHIC BACTERIA

An autotroph is an organism able to make its own food.

Autotrophic organisms take inorganic substances into their

bodies and transform them into organic nourishment.

Autotrophs are essential to all life because they are the pri-

mary producers at the base of all food chains. There are two

categories of autotrophs, distinguished by the energy each

uses to synthesize food. Photoautotrophs use light energy;

chemoautotrophs use chemical energy.

Photoautotrophic organisms (e.g., green plants) have

the capacity to utilize solar radiation and obtain their energy

directly from sunlight.

Until recently, scientists held there existed only a few

kinds of bacteriathat used chemical energy to create their own

food. Some of these bacteria were found living near vents and

active volcanoes on the lightless ocean floor. The bacteria cre-

ate their food using inorganic sulfur compounds gushing out

of the vents from the hot interior of the planet.

In 1993, scientists found many new species of

chemoautotrophic bacterialiving in fissured rock far below

the ocean floor. These bacteria take in carbon dioxide and

water and convert the chemical energy in sulfur compounds to

run metabolic processes that create carbohydrates and sugars.

A unique characteristic of these chemoautotrophic bacteria is

that they thrive at temperatures high enough to kill other

organisms. Some scientists assert that these unique bacteria

should be classified in their own new taxonomic kingdom.

See also Bacterial kingdoms; Biogeochemical cycles;

Extremophiles

AAvery, Oswald TheodoreVERY, OSWALD THEODORE(1877-1955)

Canadian-born American immunologist

Oswald Avery was one of the founding fathers of immuno-

chemistry(the study of the chemical aspects of immunology)

and a major contributor to the scientific evolutionof microbi-

ology. His studies of the Pneumococcusvirus (causing acute

pneumonia) led to further classification of the virus into many

distinct types and the eventual identification of the chemical

differences among various pneumococci viral strains. His

work on capsular polysaccharides and their role in determin-

ing immunological specificity and virulence in pneumococci

led directly to the development of diagnostic tests to demon-

strate circulating antibody. These studies also contributed to

the development of therapeutic sera used to treat the pneumo-

nia virus. Among his most original contributions to immunol-

ogy was the identification of complex carbohydrates as

playing an important role in many immunological processes.

Avery’s greatest impact on science, however, was his discov-

ery that deoxyribonucleic acid(DNA) is the molecular basis for

passing on genetic information in biological self-replication.

This discovery forced geneticists of that time to reevaluate

their emphasis on the protein as the major means of transmit-

ting hereditary information. This new focus on DNA led to

James Watsonand Francis Crick’s model of DNA in 1952 and

an eventual revolution in understanding the mechanisms of

heredity at the molecular level.

Avery was born Halifax, Nova Scotia, to Joseph Francis

and Elizabeth Crowdy Avery. His father was a native of

England and a clergyman in the Baptist church, with which

Avery was to maintain a lifelong affiliation. In 1887 the Avery

family immigrated to the United States and settled in New

York City, where Avery was to spend nearly sixty-one years of

his life. A private man, he guarded his personal life, even from

his colleagues, and seldom spoke of his past. He stressed that

research should be the primary basis of evaluation for a scien-

tific life, extending his disregard for personal matters to the

point that he once refused to include details of a colleague’s

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