Interferons & Vaccine

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.



Property Type
Alpha Beta Gamma
Current nomenclature IFN-? IFN-? IFN-?
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 cost-effective 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 nonimmune contacts No Possible
Interference by other viruses in host No Possible
Stability at room temperature High Low