Introduction to Veterinary Vaccines Flashcards
Adaptive Acquired Immunity
Two Approaches: 1. Humoral / Antibodies 2. Cell Mediated Need to recognise two distinctly different forms of foreign invaders Both aided by T helper cells
Extra-Cellular
Humoral / antibodies B Cell
Inside Cells
Cell mediated immunity Tc cells
The direction of the Th cell response governs
the nature of the immune response. Th1 promotes CMI, Th2 promotes humoral responses.
Serum antibody titre conferred by passive immunisation
Administration of antibodies from a resistant animal to a susceptible animal
Gives immediate protection but as the antibodies are broken down, the immunity diminishes
Artificial Passive Immunisation
Donor animal repeatedly immunised against antigen, then bleed. As Ab levels decrease, repeat immunisation.
Used against anthrax in cattle
distemper in dogs
panleukopenia in cats
measles in humans
Most important one raise is against Clostridium tetani and C. perfringens where Abs raised in horses
Only gives relatively short protection
Problems with Passive Immunisation
Maternal antibodies may interfere with active immune response
Do not administer pulpy kidney vaccine to lambs from vaccinated ewes until ~6-8 weeks of age
As seen in the dog, serum antibody levels will decrease quickly as regarded as foreign!
reduce response for heterologous species by pepsin treatment
However, if circulating antibodies present once the animal has mounted an immune response it can cause
Immune complex formation (type III hypersensitivity reaction called serum sickness)
If repeated dose of horse antibodies are give it may provoke IgE production and anaphylaxis!
Central features of Active Immunisation
Administration of antigen to an animal so that it responds by mounting a protective immune response
Reimmunisation or exposure to infection will provoke a secondary response
Protection is not immediate
Active Immunisation
Provides prolonged period of protection that can be boosted by repeated injection of antigen or infection
However, they must
Stimulate APC to produce appropriate cytokines
Stimulate both T and B cells
Stimulate T helper cells to sufficient epitopes to overcome MHC class II polymorphism
Must persist in appropriate sites in lymphoid tissue so that Ab production will last as long as possible
Must be safe!
Many potential vaccine failures are due to not meeting one or more of these requirements!
Antibodies in immunity against viruses
Antibodies can bind to free viruses to prevent them from entering cells (neutralisation).
Once antibody binds virus infection will not occur
virolysis
Virus in blood can be destroyed by antibodies binding to them
Virus in blood can be destroyed by antibody binding and aiding
phagocytosis by neutrophils
Factors affecting immune responses to vaccines
- Genetics: (not much can be done apart from selection)
- Age: mature animals generally respond better than young. May be due to an immature immune system or passively acquire IgG
Health: Pre-existing disease may decrease response to Ag
Nutrition: Undernutrition or deficiency reduce both IgG and CMI responses
Stress: Although considered to be suppressive, can alter Th balance towards a Th2 response
- Incorporation of Adjuvants: Compounds that provoke a stronger immune response eg. Alum (aluminium hydroxide) provides a slow release mechanism for antigen triggering a stronger response
If a live viral vaccine is used…
it will replicate within a cell. The infected cell will then process the endogenous antigen
stimulates CD8+ cells
However, early killed / inactivated vaccines acted as exogenous antigen
stimulates CD4+ cells
Attenuated / Living Vaccines
Virulent living organisms CANNOT normally be used !
Virulence must be reduced so that it still living but can no longer cause disease
Usually attenuated by prolonged tissue culture in non- host cells
Canine distemper virus usually infects lymphoid cells
repeated culture in canine kidney cells virulence is lost
Difficult to distinguish between infected and vaccinated animals based on serology!
Some animals more susceptible to live vaccines eg Afghan hounds at risk of ‘blue eye’ after CAV 1 canine hepatitis vaccines than other breeds
