- Active humoral immunity is the development of antibodies in response to stimulation by an antigen.
- Passive immunity. Once formed, those antibodies can be removed from the host and transferred into another recipient where they provide immediate passive immunity.
Tetanus antitoxin is an antiserum that has been produced by actively immunizing an animal (e.g., a horse) with tetanus toxoid.
When a human
the physician, fearing that disease symptoms may occur before the patient is able to mount an active immune response, will inject tetanus antitoxin in order to provide immediate protection.
The protection is short-lived, lasting only until the last of the injected antibodies have been catabolized.
- may have been exposed to spores of the tetanus bacillus (e.g. in a dirty puncture wound) and
- has never or not for a long time (10 years) been actively immunized with tetanus toxoid,
These antisera (raised in horses or sheep) provide immediate protection to people bitten by a venomous animal (e.g., a rattlesnake).
Horse and sheep proteins are foreign to the human patient and will, in due course, elicit an active immune response. This may lead to an allergic reaction such as
To avoid such problems, humans are often used as the source of passive antibodies.
- Some immune globulin (IG) is prepared from the gamma globulin fraction of pooled plasma from the outdated blood of several thousand blood donors on the assumption that this large pool will contain good levels of antibodies against many common diseases such as
IG is also used to provide protection to boys with X-linked agammaglobulinemia, who are unable to manufacture antibodies because of a mutation in their single (because on their X chromosome) gene for Bruton's tyrosine kinase.
- Some preparations of immune globulin are harvested from selected individual donors who have either recently recovered from the disease or who have been deliberately and intensively immunized against it. These are used to provide immediate protection against such diseases as
- The recent need for an effective treatment for people with inhalational anthrax has led to the use of plasma donated by military personnel previously actively immunized with anthrax vaccine. Soon it should be possible to prepare a purified immune globulin from this plasma. Further down the road will be the use of antianthrax monoclonal antibodies.
- Rh immune globulin (RhIg) or Rhogam is used to prevent Rh-negative mothers from becoming sensitized to the Rh antigen of their newborn child. [Discussion]
However, care must be (and is) taken to ensure that the preparations are not contaminated with human pathogens such as the
Intravenous injections of IG have helped patients with such autoimmune disorders as
- The preparation contains fewer irrelevant serum proteins and of those that remain, being human proteins,
- they are far less immunogenic
- and are catabolized more slowly than horse proteins
The therapeutic effect seems to have nothing to do with the antigen specificities (e.g., antitetanus) of the antibodies in the preparation.
Instead it is the C-region portion of the antibody molecules that provides the protection.
Animal studies suggest that it does so by binding to a class of receptors on macrophages, which inhibits them from phagocytosing antibody-coated cells, e.g.,
The spleen is packed with macrophages and is where most of red blood cell and platelet destruction occurs in these diseases (and explains why removal of the spleen so often helps the patient).
27 February 2011