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Passive Immunity

Active vs. Passive Immunity

Antisera Raised in Nonhuman Animals

Tetanus antitoxin

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.


These antisera (raised in horses or sheep) provide immediate protection to people bitten by a venomous animal (e.g., a rattlesnake).

Immune Globulin (IG)

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.

Advantages of human immune globulin

However, care must be (and is) taken to ensure that the preparations are not contaminated with human pathogens such as the

Non-antigen-specific effects of human immune globulin

Intravenous injections of IG have helped patients with such autoimmune disorders as

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).

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27 February 2011