Antibodies are classified according to the mode of immune response they are specialized for.
Ex. IgM = early systemic, IgG= late systemic, IgA = surface, IgE = allergic.

Antigen

a substance the body recognizes as foreign and reacts with specific antibody production to reject.
Ex. bacteria, virus, protozoa, parasite, pollen, toxin or cell.

Cellular Immunity (cell mediated immunity)

 Immunity mediated by T lymphocytes, or an immune response where phagocytic cells play the predominate role.

Immunity directed against a cell that is infected with a foreign organism like a virus. This is more effective then humoral immunity or antibodies, as it prevents replication of the virus. 

Cellular immunity cannot be readily measured. It can be demonstrated by challenge studies.
 

categories by which viruses are subdivided. Related but not identical groups. Cross protection by vaccines between viruses of different Clades is poor.        

 B & T lymphocytes. Once programmed to produce antibodies, memory cells retain the information and persist for the life of the animal.

Systemic memory cells can respond with antibody production, fast enough to prevent infection or prevent disease, even in the absence of an antibody titer.

Mucosal memory cells cannot respond quickly enough to prevent infection, but respond quickly to minimize the symptoms, and hopefully provide for a lesser degree of illness.

Memory cells cannot be readily measured. The only way to demonstrate memory cells is with a challenge study

An event that appears related to a result, more often than would be expected by mere chance. It does not necessarily prove cause and effect.

An example often referred to by scientists is: “ Butter keeps elephants out of the refrigerator. “ At first the correlation of these two events might appear to be a valid observation. Certainly we have butter in our refrigerators, and we have no elephants in our refrigerators. However, is butter really the cause?  With further investigation we may or may not find out that refrigerators without butter have no elephants either. And or we may find out that something else is keeping the elephants out of the refrigerator. Or we might find out that elephants are affected by the butter in such a way that they stay out of the refrigerators solely because of the butter, or in combination with another cause.

We must be careful in drawing conclusions based on temporal associations because our conclusions may or may not be correct.

categories by which bacteria are subdivided or classified. Cross protection between bacteria of different serovars is poor.

 a measure of the quantity of antibodies. The amount of antibodies required to neutralize a measured amount of antigen, expressed as the highest dilution required for neutralization. Ex 1:10, 1:160

A high titer is a rough correlation with immunity for some diseases.

A negative titer does not necessarily indicate lack of immunity, as immunity is also controlled by cellular immunity, memory cells, which can respond with antibody production when needed.

Titers do not measure or take into account memory cells or cellular immunity.

a biologic agent containing antigens, live organisms, or killed organisms, or DNA, which will stimulate the immune system of the patient to produce antibodies, and possibly cellular immunity, as well as program memory cells to provide protection against disease. A vaccine does not provide immunity; it merely stimulates the body to produce immunity. A vaccine depends on the body’s response to provide protection.

Killed vaccines –(Inactivated) for safety, to prevent reversion to virulence, the organism is killed. Adjuvants are generally required to stimulate a sufficient immune response. Depending on the antigen and adjuvant, they may or may not produce cellular immunity. Duration of immunity is generally not as long as with modified live vaccines. Examples: Rabies, Leptospirosis, and Bordetella.
 

Modified live virus vaccines –(Attenuated) the virus has been weakened or attenuated so that it should not produce the disease. MLV vaccines produce strong stimulation of the immune system because they reproduce or replicate within the host cells, providing for even more antigen.  Adjuvant is generally not needed.  Because the vaccine virus reproduces within the host cells, MLV vaccines produce cellular immunity. This immunity is directed toward future cells that become infected with the virus. This is good because it prevents any invading virus from replicating.
Duration of immunity is generally longer for MLV vaccines.
Although any vaccine can cause a fibrosarcoma, because MLV vaccines do not have adjuvant they are less likely to cause a fibrosarcoma.
 

Subunit vaccine – a piece of DNA has been removed form the virus so it is not a whole virus vaccine. This DNA will still stimulate the immune system to provide immunity against that virus
Ex: Feline leukemia vaccine – the part of the virus that suppresses the immune system has been removed.
Most FeLV vaccines are adjuvanted. Two manufacturers, Meriel- Leukat, and Intervet Protex FeLV vaccines are non –adjuvanted.
 

Subunit vectored vaccines – Purevac Rabies Vaccine, Muriel - a piece of rabies DNA is spliced onto a canary pox virus. The canary pox virus does not cause disease in the cat. The canary pox virus will enable the antigen to be presented to the immune system in such a way that good cellular immunity is produced without the need for an adjuvant.
This non-adjuvanted vaccine was developed because adjuvanted rabies vaccines are more likely to cause fibrosarcomas. MLV rabies vaccines were removed from the market because if administered to a FeLV infected cat they could revert to virulence and cause rabies. This vaccine cannot revert to virulence, it cannot possibly cause rabies.
Adjuvanted rabies vaccines have been incriminated in causing thousands of fibrosarcomas over the last 10 years. Only two fibrosarcomas are thought to have been caused by this new subunit vectored vaccine.