Immune System
Immune System, group of cells, molecules, and organs that act together to defend the body against foreign invaders that may cause disease, such as bacteria, viruses, and fungi. The health of the body is dependent on the immune system’s ability to recognize and then repel or destroy these invaders.
IMMUNITY
Most animals have systems that resist disease. The disease resistance provided by these systems is called immunity. There are two types of immunity: innate and adaptive. Innate, or nonspecific, immunity is the body’s first, generalized line of defense against all invaders. Innate immunity is furnished by barriers such as skin, tears, mucus, and saliva, as well as by the rapid inflammation of tissues that takes place shortly after injury or infection. These innate immune mechanisms hinder the entrance and spread of disease but can rarely prevent disease completely.
COMPONENTS OF THE IMMUNE SYSTEM
The ability of the immune system to mount a response to disease is dependent on many complex interactions between the components of the immune system and the antigens on the invading pathogens, or disease-causing agents.
A. Macrophage, type of white blood cell that resides in the tissues, out of the bloodstream, where it attacks foreign substances and helps the rest of the immune system identify harmful toxins, bacteria, and viruses.
B. Lymphocyte, variety of white blood cell consisting of T cells and B cells, both critical to the action of the immune system. T cells directly attack disease-causing bacteria, viruses, and toxins, and regulate the other parts of the immune system. B cells produce antibodies, which neutralize invaders or mark them for destruction by other agents of the immune system.
C. Antigen Receptors, one of the characteristics of adaptive immunity is that it is specific: Each response is tailored to a specific type of invading antigen. Each lymphocyte, as it matures, makes an antigen receptor—that is, a specific structure on its surface that can bind with a matching structure on the antigen like a lock and key. Although lymphocytes can make billions of different kinds of antigen receptors, each individual lymphocyte makes only one kind. When an antigen enters the body, it activates only the lymphocytes whose receptors match up with it.
D. Antigen-Presenting Cells - When an antigen enters a body cell, certain transport molecules within the cell attach themselves to the antigen and transport it to the surface of the cell, where they “present” the antigen to T lymphocytes. These transport molecules are made by a group of genes called the major histocompatibility complex (MHC) and are therefore known as MHC molecules. Some MHC molecules, called class I MHC molecules, present antigens to killer T cells; other MHC molecules, called class II MHC molecules, present antigens to helper T cells.
IMMUNITY
Most animals have systems that resist disease. The disease resistance provided by these systems is called immunity. There are two types of immunity: innate and adaptive. Innate, or nonspecific, immunity is the body’s first, generalized line of defense against all invaders. Innate immunity is furnished by barriers such as skin, tears, mucus, and saliva, as well as by the rapid inflammation of tissues that takes place shortly after injury or infection. These innate immune mechanisms hinder the entrance and spread of disease but can rarely prevent disease completely.
COMPONENTS OF THE IMMUNE SYSTEM
The ability of the immune system to mount a response to disease is dependent on many complex interactions between the components of the immune system and the antigens on the invading pathogens, or disease-causing agents.
A. Macrophage, type of white blood cell that resides in the tissues, out of the bloodstream, where it attacks foreign substances and helps the rest of the immune system identify harmful toxins, bacteria, and viruses.
B. Lymphocyte, variety of white blood cell consisting of T cells and B cells, both critical to the action of the immune system. T cells directly attack disease-causing bacteria, viruses, and toxins, and regulate the other parts of the immune system. B cells produce antibodies, which neutralize invaders or mark them for destruction by other agents of the immune system.
C. Antigen Receptors, one of the characteristics of adaptive immunity is that it is specific: Each response is tailored to a specific type of invading antigen. Each lymphocyte, as it matures, makes an antigen receptor—that is, a specific structure on its surface that can bind with a matching structure on the antigen like a lock and key. Although lymphocytes can make billions of different kinds of antigen receptors, each individual lymphocyte makes only one kind. When an antigen enters the body, it activates only the lymphocytes whose receptors match up with it.
D. Antigen-Presenting Cells - When an antigen enters a body cell, certain transport molecules within the cell attach themselves to the antigen and transport it to the surface of the cell, where they “present” the antigen to T lymphocytes. These transport molecules are made by a group of genes called the major histocompatibility complex (MHC) and are therefore known as MHC molecules. Some MHC molecules, called class I MHC molecules, present antigens to killer T cells; other MHC molecules, called class II MHC molecules, present antigens to helper T cells.
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