Studies that are in vitro are performed with cells or biological molecules studied outside
their normal biological context; for example proteins are examined in solution, or cells
in artificial culture medium.
Colloquially called "test tube experiments", these studies in biology and its sub-disciplines
are traditionally done in test-tubes, flasks, petri dishes etc., but which now involve the
full range of techniques used in molecular biology and larger commercial applications.
Examples of in vitro studies include: the isolation, growth and identification of microorganisms;
cells derived from multicellular organisms; subcellular components; cellular or subcellular
extracts; purified molecules; and the commercial production of antibiotics and other pharmaceutical
products.
Studies that are conducted using components of an organism that have been isolated from
their usual biological surroundings permit a more detailed or more convenient analysis
than can be done with whole organisms.
In contrast, in vivo studies are those conducted in animals including humans, and whole plants.
These may involve investigations into the pathogenesis of infections using live bacteria
or their toxins, or the effects of antibiotics or drugs etc.
Viruses, which only replicate in living cells, are studied in the laboratory in cell or tissue
culture, but many animal virologists refer to such work as being in vitro to distinguish
it from in vivo work on whole animals.
Advantages Living organisms are extremely complex functional
systems that are made up of, at a minimum, many tens of thousands of genes, protein molecules,
RNA molecules, small organic compounds, inorganic ions and complexes in an environment that
is spatially organized by membranes and, in the case of multicellular organisms, organ
systems.
For a biological organism to survive, these myriad components must interact with each
other and with their environment in a way that processes food, removes waste, moves
components to the correct location, and is responsive to signalling molecules, other
organisms, light, sound, heat, taste, touch, and balance.
This extraordinary complexity of living organisms is a great barrier to the identification of
individual components and the exploration of their basic biological functions.
The primary advantage of in vitro work is that it permits an enormous level of simplification
of the system under study, so that the investigator can focus on a small number of components.
For example, the identity of proteins of the immune system, and the mechanism by which
they recognize and bind to foreign antigens would remain very obscure if not for the extensive
use of in vitro work to isolate the proteins, identify the cells and genes that produce
them, study the physical properties of their interaction with antigens, and identify how
those interactions lead to cellular signals that activate other components of the immune
system.
Cellular responses are often species-specific, making cross-species analysis problematic.
Newer methods of same-species-targeted, multi-organ studies are available to bypass live, cross-species
testing.
Disadvantages The primary disadvantage of in vitro experimental
studies is that it can sometimes be very challenging to extrapolate from the results of in vitro
work back to the biology of the intact organism.
Investigators doing in vitro work must be careful to avoid over-interpretation of their
results, which can sometimes lead to erroneous conclusions about organismal and systems biology.
For example, scientists developing a new viral drug to treat an infection with a pathogenic
virus may find that a candidate drug functions to prevent viral replication in an in vitro
setting.
However, before this drug is used in the clinic, it must progress through a series of in vivo
trials to determine if it is safe and effective in intact organisms.
Typically, most candidate drugs that are effective in vitro prove to be ineffective in vivo because
of issues associated with delivery of the drug to the affected tissues, toxicity towards
essential parts of the organism that were not represented in the initial in vitro studies,
or other issues.
Examples Polymerase chain reaction is a method for
selective replication of specific DNA and RNA sequences in the test tube.
Protein purification involves the isolation of a specific protein of interest from a complex
mixture of proteins, often obtained from homogenized cells or tissues.
In vitro fertilization is used to allow spermatozoa to fertilize eggs in a culture dish before
implanting the resulting embryo or embryos into the uterus of the prospective mother.
In vitro diagnostics refers to a wide range of medical and veterinary laboratory tests
that are used to diagnose diseases and monitor the clinical status of patients using samples
of blood, cells or other tissues obtained from a patient.
See also Animal testing
Ex vivo In situ
In utero In vivo
In silico In papyro
In natura In Vitro Cellular & Developmental Biology
- Animal In Vitro Cellular & Developmental Biology
- Plant Slice preparation
Notes