Biomedical Engineering Reference
In-Depth Information
IFN-γ is evolutionarily distinct from the other interferons; it binds to a separate receptor and
induces a different range of biological activities. It is thus often referred to as type II interferon.
Owing to their biological activities most interferons are of actual or likely use in the treatment
of many medical conditions, including:
•
augmentation of the immune response against infectious agents (viral, bacterial, protozoal, etc.);
•
treatment of some autoimmune conditions;
•
treatment of certain cancer types.
Interferons may be detected and quantifi ed using various bioassays or by immunoassay systems.
Although such assays were available, subsequent purifi cation, characterization and medical utili-
zation of interferons initially proved diffi cult due to the tiny quantities in which these regulatory
proteins are produced naturally by the body. By the early 1970s, advances in animal cell culture
technology, along with the identifi cation of cells producing increased concentrations of interfer-
ons, made some (mostly IFN-αs) available in reasonable quantities. It was not until the advent
of genetic engineering, however, that all interferons could be produced in quantities suffi cient to
satisfy demand for both pure and applied purposes.
8.2.1 The biochemistry of interferon-
α
For many years after its initial discovery it was assumed that IFN-α represented a single gene
product. It is now known that virtually all species produced multiple, closely related IFN-
s.
Purifi cation studies from the 1970s on using high-resolution chromatographic techniques (mainly
ion-exchange and gel-fi ltration chromatographies, immunoaffi nity chromatography and isoelec-
tric focusing) fi rst elucidated this fact.
In humans, at least 24 related genes or pseudo-genes exist that code for the production of at
least 16 distinct mature IFN-αs. These can be assigned to one of two families, i.e. type I and II.
Humans are capable of synthesizing at least 15 type I IFN-
α
.
Most mature type I IFN-αs contain 166 amino acids (one contains 165), whereas type II IFN-α is
composed of 172 amino acids. All are initially synthesized containing an additional 23-amino-acid sig-
nal peptide. Based upon amino acid sequence data, the predicted molecular mass of all IFN-αs is in the
19-20 kDa range. SDS-PAGE analysis, however, reveals observed molecular masses up to 27 kDa. Iso-
electric points determined by isoelectric focusing range between 5 and 6.5. The heterogeneity observed
is most likely due to O-linked glycolylation, although several IFN-
α
s and a single type II IFN-
α
s are not glycosylated. Some IFN-
αs also exhibit natural heterogeneity due to limited proteolytic processing at the carboxyl terminus.
Individual IFN-
α
s generally exhibit in excess of 70 per cent amino acid homology with each
other. They are rich in leucine and glutamic acid, and display conserved cysteines (usually at
positions 1, 29, 99 and 139). These generally form two disulfi de bonds in the mature molecule.
Their tertiary structures are similar, containing several α helical segments, but appear devoid of
β
α
sheets.
Individual members of the IFN-α family each have an identifying name. In most cases the names
were assigned by placing a letter after the '
α
' (i.e. IFN-
α
A, IFN-
α
B, etc.). However, some exceptions
Search WWH ::
Custom Search