Modern Biotechnology by Stephanie Stockwell

Modern Biotechnology by Stephanie Stockwell

Author:Stephanie Stockwell
Language: eng
Format: epub
Publisher: Momentum Press
Published: 2016-05-11T16:00:00+00:00


3.2.3 DISEASE PREVENTION

Many individual incidences of disease can be avoided if public health agencies respond to threats quickly, as a result of fast and accessible molecular diagnostics. That said, vaccination is the primary mode by which biotechnology can assist in the prevention of disease.

3.1.1.1 Principles of Immune Responses and Vaccination

The mammalian immune system is a highly diverse collection of cells that recognize and respond to foreign, or nonself, molecules. Such molecules are called antigens. Some anatomic features offer nonspecific protection against disease. These include skin, the low pH of digestive and female reproductive organs, beating cilia within lungs, and phagocytic cells that patrol tissues looking for foreign objects to engulf and destroy. All of these examples, and more, are part of the innate immune system.

Acquired immunity is developed when specialized cells of the immune system (i.e., B and T cells) bind and respond to an antigen. Each time the immune system encounters the antigen, the speed and strength of the response is greater. This is the principle behind vaccination. That is, if the immune system is artificially introduced to an antigen (i.e., a primary exposure) prior to a natural exposure, it will react with enough gusto to protect the host from disease when it encounters it again (i.e., secondary exposure). Memory B and T cells mediate speedy secondary and subsequent responses. To appreciate this process, it’s helpful to understand the cells and events associated with immune responses.

B and T cells constantly migrate throughout the lymphatic system; the channels and nodes that run parallel to the veins and arteries of the circulatory system. Both B and T cells bind to antigens via cell surface receptors, aptly called B and T cell receptors (BCR, TCR, respectively). Every B and T cell is covered with a unique version of the corresponding surface receptor. These differences at a population level allow distinct antigens to bind individual cells. The more diverse the cellular pool, the more adept the immune system.

T cells secrete immune cell effector molecules, called cytokines, when they bind to an antigen. B cells respond to T cell cytokines when they are concurrently bound to the same antigen. B cells are a type of antigen presenting cell (APC) that engulf, degrade, and display antigens on their surface. This process is mediated by surface BCRs and major histocompatibility complex28 (MHC) proteins. A T cell becomes activated when an antigen that matches its TCR is displayed in the context of a presenting cell’s MHC molecule.

There are two main classes of T cells—T helper and T killer. These cells are distinguished by cell surface markers that allow them to respond to antigens that derive from within host cells (e.g., viral proteins, mutant cancer-associated proteins) or the phagocytosis of extracellular materials (e.g., bacterial cells or toxins, escaped virions). T killer cells respond to intracellular-derived antigens. When activated, they release cytotoxic molecules that kill neighboring cells. This action is similar to a grenade going off—everything within the immediate area is affected. As a result, the abnormal (infected or mutant) cells that are the source of the antigen are destroyed.



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