Interferons
Interferons (IFNs) are host-coded proteins that are members of the large
cytokine family and which inhibit viral replication. They are produced
very quickly (within hours) in response to viral infection or other
inducers and are one of the body's first responders in the defense against
viral infection. Interferons are central to the innate antiviral immune
response. They also modulate humoral and cellular immunity and have
broad cell growth regulatory activities.
Properties of Interferons
There are multiple species of interferons that fall into three general
groups as follow:
Table 2. Properties of Human Interferons.
Type
Property
Alpha
Beta
Gamma
Current nomenclature
IFN-α
IFN-β
IFN-γ
Former designation
Leukocyte
Fibroblast
Immune
interferon
Type designation
Type I
Type I
Type II
Number of genes that code
for family
20
1
1
Principal cell source
Most cell
types
Most cell
types
Lymphocytes
Inducing agent
Viruses;
dsRNA
Viruses;
dsRNA
Mitogens
Stability at pH 2.0
Stable
Stable
Labile
Introns in genes
No
No
Yes
Chromosomal location of
genes
9
9
12
Size of secreted protein
(number of amino acids)
165
166
143
Chromosomal location of
IFN receptor genes
21
21
6
Viral Vaccines
The purpose of viral vaccines is to utilize the immune response of the
host to prevent viral disease. Several vaccines have proved to be effective
at reducing the incidence of viral disease Vaccination is the most costeffective method of prevention of serious viral infections.
Mucosal immunity (local IgA) is important in resistance to infection
by viruses that replicate exclusively in mucosal membranes (rhinoviruses,
influenza viruses, rotaviruses). Viruses that have a viremic mode of
spread (polio, hepatitis, measles) are controlled by serum antibodies.
Cell-mediated immunity also is involved in protection against systemic
infections (measles, herpes).
Table 3 Comparison of Characteristics of Killed and Live Viral Vaccines
Characteristic
Killed
Vaccine
Live
Vaccine
Number of doses
Multiple
Single
Need for adjuvant
Yes
No
Duration of immunity
Shorter
Longer
Effectiveness of protection (more closely
mimics natural infection)
Lower
Greater
Immunoglobulins produced
IgG
IgA and
IgG
Mucosal immunity produced
Poor
Yes
Cell-mediated immunity produced
Poor
Yes
Residual virulent virus in vaccine
Possible
No
Reversion to virulence
No
Possible
Excretion of vaccine virus and transmission to No
nonimmune contacts
Possible
Interference by other viruses in host
No
Possible
Stability at room temperature
High
Low