Immune Sera

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Chapter: Pharmaceutical Microbiology : The Manufacture And Quality Control Of Immunological Products

Immune sera are preparations derived from the blood of animals, usually horses, but mules, donkeys, sheep or goats are also used. The animals must be in good health, free of infections and obtained from sources free of transmissible spongiform encephalopathies, and kept under veterinary supervision.


 IMMUNE  SERA

 

A)          Preparation

 

Immune sera are preparations derived from the blood of animals, usually horses, but mules, donkeys, sheep or goats are also used. The animals must be in good health, free of infections and obtained from sources free of transmissible spongiform encephalopathies, and kept under veterinary supervision. To prepare an immune serum, horses or other animals are injected with a sequence of spaced doses of an antigen until a trial blood sample shows that the injections have induced a high titre of antibody to the injected antigen. An adjuvant may be used if required. A large volume of blood is then removed by venepuncture and collected into a vessel containing sufficient citrate solution to prevent clotting. The blood cells are allowed to settle and the supernatant plasma is drawn off. Alternatively, the blood can be mechanically defibrinated. The crude plasma can be sterilized by filtration and dispensed for use, but it is preferable to fractionate it to separate the immune globulin. This is done by fractional precipitation of the plasma by the addition of ammonium sulphate. The globulin fraction is recovered and treated with pepsin to yield a refined immune product containing the Fab fragment. This refined globulin contains no more than a trace of the albumin and other proteins that were present in the plasma. It is less antigenic, has a longer half-life in the circulation and is less likely to provoke anaphylaxis or serum sickness than whole serum or crude globulin (Harms, 1948). The antibody content of the refined product is determined by specific assay, the product is diluted to the required concentration and transferred into ampoules. Two or more monovalent immune sera may be blended together to provide a multivalent immune serum.

 

B)                        Quality Control

 

The quality of immune sera is controlled by potency tests and by conventional tests for safety and sterility. The potency tests have a common design in that, in the case of all immune sera, the potency is estimated by comparing the amount of the product that is required to neutralize an effect of a homologous toxin with the amount of a standard preparation that is required to achieve the same effect. Serial dilutions of the immune serum and of a standard preparation are made and to each is added a constant amount of the homologous antigen. Each mixture is then inoculated into a group of animals, usually guinea-pigs or mice, and the dilutions of the immune serum and of the standard, which neutralize the effects of toxin, are noted. As the potencies of the standard preparations are expressed in IU, the potencies of the immune sera are determined in corresponding units per millilitre (British Pharmacopoeia, 2010).The quality of globulin fractions is usually monitored by gel electrophoresis to detect contaminating proteins and uncleaved immunoglobulin,and by size-exclusion high-performance liquid chromatography to detect aggregates and small fragments. The immune sera are also tested for contaminating viruses by inoculation on to cell cultures capable of detecting a wide range of viruses relevant to the particular product.

 


 

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