0.3 Immune system module 4: the adaptive immune response: b  (Page 2/20)

IgG    is the main antibody of secondary responses in the blood. IgG is an antibody that clears pathogens from the blood and can activate complement proteins. This class of antibody is the one that crosses the placenta to protect the developing fetus from disease.

IgA    exists in exocrine gland secretions of the mucous membranes, including mucus, saliva, and tears. Thus, IgA is the only antibody to leave the interior of the body to protect body surfaces. IgA is also of importance to newborns, because this antibody is present in mother’s breast milk (colostrum), which serves to protect the infant from disease.

IgE    is usually associated with allergies and anaphylaxis. It is present in the lowest concentration in the blood. IgE is very specific, such that if a person is allergic to peanuts, there will be peanut-specific IgE bound to his or her cells. In this person, eating peanuts will have a severe allergic reactions, including anaphylaxis , a severe, systemic allergic response that can cause death.

IgD    signals the B cells to be activated. By being activated, they are ready to take part in the defense of the body in the immune system. IgD also plays a role in protecting our respiratory systems from bacteria.

Active versus passive immunity

Immunity to pathogens, and the ability to control pathogen growth so that damage to the tissues of the body is limited, can be acquired by (1) the active development of an immune response in the infected individual or (2) the passive transfer of immune components from an immune individual to a nonimmune one. Both active and passive immunity have examples in the natural world and as part of medicine.

Active immunity is the resistance to pathogens acquired during an adaptive immune response within an individual. ( [link] ) More simply, active immunity occurs when you make your own antibodies. Naturally acquired active immunity , is the response to a pathogen which has invaded one's body that leads to the manufacture of antibodies. Artificially acquired active immunity involves the use of vaccines. A vaccine is a killed or weakened pathogen that, when administered to a healthy individual, leads to the development of antibodies without causing much in the way of symptoms. Thus, with the use of vaccines, one can avoid the damage from disease that results from the first exposure to the pathogen, yet reap the benefits of protection from antibodies. Although you make your own antibodies, a vaccine is considered to be artificial immunity since it needs to be administered to you. The discovery of vaccines was one of the major medical advances of the twentieth century and led to the wipe out of smallpox and the control of many infectious diseases, including polio, measles, and whooping cough.

Passive immunity arises from the transfer of antibodies to an individual without requiring them to create their own antibodies. Naturally acquired passive immunity is seen during fetal development. IgG is transferred from the maternal circulation to the fetus via the placenta, protecting the fetus from infection and protecting the newborn for the first few months of its life. A newborn benefits from the IgA antibodies it obtains from milk during breastfeeding. The fetus and newborn thus benefit from the antibodies of the mother to the pathogens to which she has been exposed. In medicine, artificially acquired passive immunity usually involves injections of immunoglobulins, taken from people or animals previously exposed to a specific pathogen. This treatment is a fast-acting method of temporarily protecting an individual who was possibly exposed to a pathogen. The downside to both types of passive immunity is the lack of ability to create their own antibodies. Once the antibodies are transferred, they are effective for only a limited time before they degrade. Once again an example such as breastfeeding is natural immunity, since it happens without medical administration. Immunoglobulins are considered artificial immunity since they have to be administered.