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21.4 The Adaptive Immune Response: B-lymphocytes and Antibodies
Antibodies were the first component of the adaptive immune response to be characterized by scientists working on the immune system. It was already known that individuals who survived a bacterial infection were immune to re-infection with the same pathogen. Early microbiologists took serum from an immune patient and mixed it with a fresh culture of the same type of bacteria, then observed the bacteria under a microscope. The bacteria be- came clumped in a process called agglutination. When a different bacterial species was used, the agglutination did not happen. Thus, there was something in the serum of im- mune individuals that could specifically bind to and agglutinate bacteria.
21.5 The Adaptive Immune Response: B-lymphocytes and Antibodies
Now that you understand the development of mature, na.ve B cells and T cells, and some of their major functions, how do all of these various cells, proteins, and cytokines come together to actually resolve an infection? Ideally, the immune response will rid the body of a pathogen entirely. The adaptive immune response, with its rapid clonal expansion, is well suited to this purpose. Think of a primary infection as a race between the pathogen and the immune system. The pathogen bypasses barrier defenses and starts multiplying in the host’s body.
During the first 4 to 5 days, the innate immune response will partially control, but not stop, pathogen growth. As the adaptive immune response gears up, however, it will begin to clear the pathogen from the body, while at the same time becoming stronger and stronger. When following antibody responses in patients with a particular disease such as a virus, this clearance is referred to as seroconversion (sero- = “serum”).
Seroconversion is the reciprocal relationship between virus levels in the blood and anti- body levels. As the antibody levels rise, the virus levels decline, and this is a sign that the immune response is being at least partially effective (partially, because in many diseases, seroconversion does not necessarily mean a patient is getting well).
21.6 Diseases Associated with Depressed or Overactive Immune Responses
This section is about how the immune system goes wrong. When it goes haywire, and be- comes too weak or too strong, it leads to a state of disease. The factors that maintain immu- nological homeostasis are complex and incompletely understood. As you have seen, the immune system is quite complex. It has many pathways using many cell types and signals. Because it is so complex, there are many ways for it to go wrong. Inherited immunodefi- ciencies arise from gene mutations that affect specific components of the immune re- sponse. There are also acquired immunodeficiencies with potentially devastating effects on the immune system, such as HIV.
Components of the immune system cause four types of hypersensitivity. Notice that types I–III are B cell mediated, whereas type IV hypersensitivity is exclusively a T cell phenome- non. The worst cases of the immune system over-reacting are autoimmune diseases. Somehow, tolerance breaks down and the immune systems in individuals with these dis- eases begin to attack their own bodies, causing significant damage. The trigger for these
21.4 OBJECTIVES
1. Explain how B cells mature and how B cell tolerance develops
21.6 OBJECTIVES
1. Give an example of how autoimmune disease breaks tolerance
21.5 OBJECTIVES
1. Explain the development of immunological competence
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State of Alaska EMS Education Primer - 2016
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