expression system A host organism combined with a genetic vector (such as a virus or circular DNA molecule called a plasmid) that is loaded with a gene of interest. The expression system provides the genetic context in which a gene will function in the cell — that is, the gene will be expressed as a protein.

expression vector A virus, plasmid, cosmid, or artificial chromosome that delivers foreign genes to a host, creating a recombinant organism that will express the desired protein.

extractables Substances withdrawn (such as the medicinally active components of plant or animal tissue) by a physical or chemical process. 2. Materials that are actually removed from a container or closure by a given formulation or product. (See leachables).

extrusion A process of forming rods, tubes, or other continuously formed pieces by pushing hot or cold semisoft solid material through a die; also any process of pushing a substance through holes or a tube.

F

Fab Antigen-binding fragment of an immunoglobulin. An IgG Fab is prepared by enzymatic cleavage of the intact tetrameric IgG, and reduction of the inter-chain disulfide links, and binds one mole of antigen per mole. {See F(ab)'2}

F(ab)'2 Dimeric antigen-binding fragment of an immunoglobulin. An IgG F(ab)'2 is prepared by enzymatic digestion of the intact IgG, which removes the Fc portion of the molecule. F(ab)'2 binds two moles of antigen per mole. (See Fab)

FAb Antibodies are Y-shaped molecules. The "arms" of each Y are the FAb regions (fragment antigen binding sites) that bind to antigens; the stem of the Y is the Fc region, which attracts microbe-engulfing cells to destroy what has been bound. If the active part of an antibody can be identified, sometimes only that part of it may be needed as a therapeutic molecule (facilitating production and processing by reducing the size and lessening the chances of an immune response in patients who receive the drug). This fragment may be "conjugated" to another molecule (such as PEG) for stability or other reasons.

factors (coagulation factors) Protein constituents of blood, numbered according to the order in which they were discovered, which separate out in a traditional fractionation procedure (Cohn fractionation); Factor VIII, for example, is a blood serum protein involved in clot formation that is also called antihemophilic globulin.

Fc Portion of an immunoglobulin molecule that carries various effector functions, such as the ability to bind complement. Important in immunological activities, and separable from the antigen-binding portion by enzymatic or chemical cleavage. (See Fab)

FD&C Act Food, Drug and Cosmetic Act of 1938; the major legislation regulating such products in the United States. It requires companies to prove that their products are safe before marketing them, extends FDA oversight to cosmetics and therapeutic devices, explicitly authorizes factory inspections, requires standards for food, and adds injunctions to previous penalties of seizure and criminal prosecution for violations of related laws.

FDA Food and Drug Administration

FDA-483 A form prepared at the conclusion of an inspection (without review by FDA management) citing observations that may constitute violations of law, in the opinion of the inspector. Originally intended to inform companies of possible product adulteration so that prompt corrective action could be taken, 483s now list a host of observations. Accessible through the Freedom of Information Act by competitors, potential customers, and the media, 483s can lead to withholding of product approvals, may come into play in due diligence phases of acquisitions and mergers, and can potentially cost companies money.