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Biological products used to induce immunity to various infectious diseases or noxious substances of biological origin. The term is usually limited to immune serums, antitoxins, vaccines, and toxoids that have the effect of providing protective substances of the same general nature that a person develops naturally from having survived an infectious disease or having experienced repeated contact with a biological poison. As a matter of governmental regulatory convenience, certain therapeutic substances which have little to do with conferring immunity have been classified as biological products primarily because they are derived from human or animal sources and are tested for safety by methods similar to those used for many biological products. See Immunity

One major class of biologicals includes the animal and human immune serums. All animals, including humans, develop protective substances in their blood plasma during recovery from many (but not all) infectious diseases or following the injection of toxins or killed bacteria and viruses. These protective substances, called antibodies, usually are found in the immunoglobulin fraction of the plasma and are specific since they react with and neutralize only substances identical or closely similar to those that caused them to be formed. See Antibody, Immunoglobulin, Serum

Antibody-containing serum from another animal is useful in the treatment, modification, or prevention of certain diseases of humans when it is given by intramuscular or intravenous injection. The use of these preformed “borrowed” antibodies is called passive immunization, to distinguish it from active immunization, in which each person develops his or her own antibodies. Passive immunization has the advantage of providing immediate protection, but it is temporary because serum proteins from other animals and even from other humans are rapidly destroyed in the recipient.

Serums which contain antibodies active chiefly in destroying the infecting virus or bacterium are usually called antiserums or immune serums; those containing antibodies capable of neutralizing the secreted toxins of bacteria are called antitoxins. Immune serums have been prepared to neutralize the venoms of certain poisonous snakes and black widow spiders; they are called antivenins.

Because all products used for passive immunization are immune serums, or globulin fractions from such serums, they are named to indicate the diseases that they treat or prevent, the substances that they inhibit or neutralize, the animal from which they came, and whether they are whole serums or the globulin fractions thereof. Thus there is, for example, antipertussis immune rabbit serum, measles immune globulin (human), diphtheria antitoxic globulin (horse), tetanus immune globulin (human), and anti-Rh0 (D) gamma globulin (human).

The use of animal immune serums for prevention of therapy in humans has certain disadvantages. The serum proteins themselves may cause the production of specific antibodies in the recipient of the immune serum, and thus the person may become allergically sensitized to the serum protein of this animal species. See Anaphylaxis, Hypersensitivity

Products used to produce active immunity constitute the other large class of biological products. They contain the actual toxins, viruses, or bacteria that cause disease, but they are modified in a manner to make them safe to administer. Because the body does not distinguish between the natural toxin or infectious agent and the same material when properly modified, immunity is produced in response to injections of these materials in a manner very similar to that which occurs during the natural disease. Vaccines are suspensions of the killed or attenuated (weakened) bacteria or viruses or fractions thereof. Toxoids are solutions of the chemically altered specific bacterial toxins which cause the major damage produced by bacterial infections. Biological products producing active immunity are usually named to indicate the disease they immunize against and the kind of substance they contain: thus typhoid vaccine, diphtheria toxoid, tetanus toxoid, measles vaccine, mumps vaccine, and poliomyelitis vaccine. See Vaccination

Another group of biological products consists of reagents used in the diagnosis of infectious diseases. These include immune serums for the serological typing and identification of pathogenic bacteria and viruses, and various antigens for the detection of antibodies in patients' serums as a means of assisting in diagnosis.

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