There are two general types of immunity to disease organisms, active immunity and passive immunity. Both types of immunity involve antibodies against a specific disease organism. Active immunity involves a complicated antibody-mediated immune response against antigens of the disease microbe. Since you actively produce the antibodies, this is called active immunity. In fact, some vaccines may even cause temporary discomfort, such as mild fever and muscular pain. The antibodies go on a "search and destroy" mission throughout your circulatory system. Their target is a specific microbe, such as a bacterium or virus. When the antigen combining sites of the Y-shaped immune (IgG) antibody recognize a specific antigen on the surface of a bacterium or virus, they bind to the antigen. Through a series of reactions the disease microbes are broken down and engulfed by special white blood cells (WBCs) called phagocytes. It should be noted here that antibodies also occur in many other groups of animals, including mammals, birds, amphibians, fish and invertebrates.

When vaccinated, you typically receive an intramuscular or subcutaneous injection of a vaccine. [The Sabin polio vaccine may be taken orally.] The vaccine contains a preparation made from a specific disease organism, such as polio, smallpox, whooping cough, typhus, bubonic plague, yellow fever, swine flu, etc. There is even a vaccine for anthrax, although it is currently (2001) in short supply and not available to the general population. Some vaccines are made from a weakened or dead strain of the actual organism. Other vaccines, such as Hepatitis B, are made from the genetically-engineered outer protein coat of the virus. Smallpox vaccine is made from a related virus called the cowpox virus. The dual immunity to these diseases came from the discovery that milkmaids (dairymaids) had developed an immunity to cow pox that also made them immune to smallpox. Multivalent (polyvalent) vaccines contain antigens of more than one microbe and induce antibody production against several disease organisms.

Most vaccinations require several injections in a series in order to provide immunity. In fact, the rabies vaccination involves more than 20 intramuscular injections in the abdomen; however, a more recent vaccine requires only five injections in the arm. Some vaccines are administered in the hip region because there are fewer nerves in this area. Your immune system responds to the vaccination by producing antibodies. Special ribosome-rich WBCs called plasma cells produce the actual antibodies. Plasma cells originate from WBCs called B-lymphocytes that are produced by lymphocyte stem cells in the bone marrow. The B-lymphocytes also produce special WBCs called memory cells which remain in your system for many years. The memory cells "remember" the specific disease organism and respond rapidly to a subsequent infection of the same organism by producing more plasma cells. Because of the production of memory cells, vaccines may prevent infections for many years. Some vaccines, such as diphtheria and tetanus, are made from soluble toxins rather than the actual organism. The toxins have been chemically altered and rendered harmless, but still induce antibody production. They are called toxoids because the are made from modified toxins of the organism. Like the B-lymphocytes, T-lymphocytes (T-cells) are also produced in the bone marrow. T-cells are another body defense mechanism called the cell-mediated immune response. This complicated immune response involves helper T-cells, effector T-cells, suppressor T-cells and killer T-cells. See the following link about poison oak, a remarkable cell-mediated immune response.

Passive immunity involves the intramuscular injection of a serum or antiserum containing ready-made antibodies. The antibodies are produced by another person or animal who has been exposed to specific antigens of a disease organism or toxin. If the serum is made from a toxin (such as tetanus toxin) it is called an antitoxin. Gamma globulin is the globular protein fraction of human blood containing many different antibodies. It is sometimes given for hepatitis A, immunodeficiency diseases, and other illnesses in which the immune system has been compromised. Gamma globulin is also given to boost the immune system prior to departing for a foreign country. Special precautions must be taken when administering serums containing antibodies made from other animals, such as goats and horses. Serums of equine origin (sometimes called horse serums) may trigger severe allergic reactions in hypersensitive people. These allergic reactions can be fatal if not treated quickly.

The RhoGamŪ given to an Rh negative woman after giving birth to an Rh positive baby is actually a serum containing anti-Rh antibodies. The antibodies seek out and destroy any residual Rh positive RBCs from the fetus that may have entered the mother's circulatory system. If the positive RBCs are destroyed in time, the mother will not be stimulated to produce anti-Rh antibodies. This is desirable in case she has another Rh positive baby. The RhoGamŪ serum contains anti-Rh antibodies obtained from Rh negative men who have been exposed to the Rh antigen (Rh positive RBC) or from Rh negative woman beyond child-bearing age or who will never bear children.

Rattlesnake antivenin is a polyvalent serum containing antibodies against several species of pit vipers of the family Crotalidae, including rattlesnakes (Crotalus), copperheads & cottonmouth moccasins (Agkistrodon), fer-de-lance (Bothrops) and bushmaster (Lachesis). Pit vipers are readily identified by their heat sensitive loreal pit between each eye and nostril. Horses are injected with venom to stimulate antibody production. Antibodies are removed from the horse's blood by centrifugation. The antibodies bind to the protein toxins of the injected venom, resulting in the destruction of the toxin before it damages blood cells and tissues of the victim.

Hemotoxins of pit vipers, such as rattlesnakes, can cause severe damage to tissues in the vicinity of the bite, and can cause gangrene in the afflicted extremities. Baby rattlesnakes generally inject all of their available venom, while large rattlesnakes may only inflict a "dry bite" resulting in fang punctures and bacteria without venom. They apparently strike and bite in a purely defensive action. This is why young rattlesnakes are often considered more dangerous. If the large rattlesnake injects a full-venom bite, it is considerably more dangerous. One of the reasons bites of the Central and South American bushmaster and fer-de-lance are especially dangerous to people is the volume of venom injected by these large pit vipers. Gram for gram, there are snakes of the cobra family with more deadly venoms. Large New World pit vipers have very effective movable fangs in the front of their jaws that literally stab their prey with a lethal dosage of venom. Other antivenins are available for venomous snakes of the viper family (Viperidae), cobra family (Elapidae) and sea snake family (Hydrophiidae). Some of these snakes have potent neurotoxic venoms that effect the nervous system of their prey.

Antivenin kit for North and South American pit vipers (Crotalidae). The kit includes a vial of freeze-dried, crystalized antivenin (A), a test vial (B), a syringe containing sterile water (C), and a plastic needle cover that serves as a push-pull rod when screwed into the rubber plunger on the syringe. The syringe is injected into the vial of antivenin crystals. The dissolved antivenin is then withdrawn back into the syringe. A drop from the test vial is used to perform a subcutaneous test. A wheal characterized by a circular reddish swelling indicates hypersensitivity to horse serums. The test drop can also be applied to the conjunctiva of the eye. Antivenin should only be administered by medical specialists who are trained to respond to possible lethal allergic reactions.