Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY In vitro and in vivo research

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rejected much more quickly. This led him to propose that an

immunological response was at play in the rejection of trans-

planted material. This led to the first successful transplant in

1954, when the kidney of one identical twin was transplanted

to the other twin. In the twins, the absence of genetic differ-

ences in their tissues would eliminate an immunological

response.

As the role of the immune system in transplantation fail-

ure became more clear, the use of compounds to suppress the

immune system began in the 1960s. In the 1960s and 1970s,

the antigenic basis of immune recognition of foreign and non-

foreign tissue became evident. With these discoveries came

the recognition that the suppression of the immune system

could aid in maintaining transplanted tissue. Successful trans-

plantation of the liver was achieved in 1963, of the heart and

small bowel in 1967.

In the 1980s, cyclosporin was discovered and shown to

be effective in maintaining transplanted material. The clinical

use of cyclosporin became standard. By the end of that decade,

the use of immunosuppressant drugs just prior to and forever

after a transplant had boosted the one-year transplant success

rate to more than 80 per cent for all transplants except for the

small intestine. In the present day, the survival rate of a kidney

transplant is 86 percent even after five years.

Immunosuppressant drugs have other uses as well.

Suppressing the immune system can lessen the disfigurement

caused by severe forms of skin disorders such as psoriasis.

Other examples include rheumatoid arthritis, Crohn’s disease

(which is an ongoing inflammationof the intestinal tract) and

alopecia areata (nonuniform hair loss). In such cases the use of

immunosuppressant therapy needs to be evaluated carefully,

especially when the condition is not life threatening. This is

because the deliberate suppression of the immune system can

leave the individual vulnerable to other infections. Also, the

clotting of blood can be inhibited, which could produce

uncontrolled bleeding.

Another potential risk in the use of immunosuppres-

sant drugs involves the administration of vaccines. The use

of vaccines is not advisable when immunosuppressant drugs

are being used, especially vaccines that utilize living but

weakened bacteriaor a virus as the agent designed to elicit

protection. The deliberately immunocompromised individual

could develop the disease for which the vaccineis intended

to prevent.

The same risk analysis applies to the possible side

effects of immunosuppressant drugs, which can include a

higher than normal risk of developing some kinds of cancer

later in life. The link between immunosuppressant drugs and

cancer is not yet clear. The link was assumed to be a conse-

quence of the interference with the ability of the body to detect

and respond to cancerous cells. Conversely, cancer develop-

ment has been viewed as being due partially to a failure of the

immune system. Yet people with acquired immunodeficiency

system, whose immune systems are also compromised, do not

show increased rates of cancer. Instead, immunosuppressant

drugs such as cyclosporine may themselves encourage the

development of cancer by activating a cellular factor that

makes cells more invasive.

It is now well known that the deliberate suppression of

the immune system carries risks. However, the risks of a side

effect or developing another illness, is usually less than the

immediate health risk associated with not suppressing the

immune system.

See also Autoimmunity and autoimmune diseases;

Immunodeficiency

IIn vitroN VITROand in vivoresearch ANDIN VIVORESEARCH

In vitroresearch is generally referred to as the manipulation of

organs, tissues, cells, and biomolecules in a controlled, artifi-

cial environment. The characterization and analysis of bio-

molecules and biological systems in the context of intact

organisms is known as in vivoresearch.

The basic unit of living organisms is the cell, which in

terms of scale and dimension is at the interface between the

molecular and the microscopic level. The living cell is in turn

divided into functional and structural domains such as the

nucleus, the cytoplasm, and the secretory pathway, which are

composed of a vast array of biomolecules. These molecules of

life carry out the chemical reactions that enable a cell to inter-

act with its environment, use and store energy, reproduce, and

grow. The structure of each biomolecule and its subcellular

localization determines in which chemical reactions it is able

to participate and hence what role it plays in the cell’s life

process. Any manipulation that breaks down this unit of life,

that is, the cell into its non-living components is, considered

an in vitroapproach. Thus, in vitro,which literally means “in

glass,” refers to the experimental manipulation conducted

using cell-free extracts and purified or partially purified bio-

molecules in test tubes. Most of the biochemical and molecu-

lar biological approaches and techniques are considered

genetic manipulation research. Molecular cloningof a gene

with the aim of expressing its protein product includes some

steps that are considered in vitroexperiments such as the PCR

amplification of the gene and the ligation of that gene to the

expression vector. The expression of that gene in a host cell is

considered an in vivoprocedure. What characterizes an in

vitroexperiment is in principle the fact the conditions are arti-

ficial and are reconstructions of what might happen in vivo.

Many in vitroassays are approximate reconstitutions of bio-

logical processes by mixing the necessary components and

reagents under controlled conditions. Examples of biological

processes that can be reconstituted in vitroare enzymatic reac-

tions, folding and refolding of proteins and DNA, and the repli-

cation of DNA in the PCR reaction.

The definition of in vitroand in vivoresearch depends

on the experimental model used. Microbiologists and yeast

geneticists working with single cells or cell populations are

conducting in vivoresearch while an immunologist who works

with purified lymphocytes in tissue cultureusually considers

his experiments as an in vitroapproach. The in vivoapproach

involves experiments performed in the context of the large

system of the body of an experimental animal. In the case of

in vitrofertilization, physicians and reproductive biologists

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