The Immune System - Business English | Trường Đại học Hùng Vương

`The Immune System What is the immune system?
The immune system is a network of biological processes that protects an organism from diseases. It detects and
responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects
such as wood splinters, distinguishing them from the organism's own healthy tissue.
There are 2 main parts of the immune system:
The innate immune system. You are born with this.
The adaptive immune system. You develop this when your body is exposed to microbes or chemicals released by microbes.
⇒ These 2 immune systems work together. The innate immune system
The innate immune system is made of defenses against infection that can be activated immediately once a
pathogen attacks. The innate immune system is essentially made up of barriers that aim to keep viruses,
bacteria, parasites, and other foreign particles out of your body or limit their ability to spread and move
throughout the body. The innate immune system includes: ●
Physical Barriers such as skin, the gastrointestinal tract, the respiratory tract, the nasopharynx, cilia, eyelashes and other body hair. ●
Defense Mechanisms such as secretions, mucous, bile, gastric acid, saliva, tears, and sweat. ●
General Immune Responses such as inflammation, complement, and non-specific cellular responses.
The innate immune system is always general, or nonspecific, meaning anything that is identified as foreign or
non-self is a target for the innate immune response. The innate immune system is activated by the presence of
antigens and their chemical properties.
Cells of the Innate Immune System ●
Phagocytes, or Phagocytic cells: Phagocyte means “eating cell”, which describes what role phagocytes
play in the immune response. Phagocytes circulate throughout the body, looking for potential threats, like
bacteria and viruses, to engulf and destroy. ●
Macrophages: Macrophages are efficient phagocytic cells that can leave the circulatory system by
moving across the walls of capillary vessels. The ability to roam outside of the circulatory system is
important, because it allows macrophages to hunt pathogens with less limits. Macrophages can also
release cytokines in order to signal and recruit other cells to an area with pathogens. ●
Neutrophils: Neutrophils are phagocytic cells that are also classified as granulocytes because they
contain granules in their cytoplasm. These granules are very toxic to bacteria and fungi, and cause them
to stop proliferating or die on contact. The bone marrow of an average healthy adult makes approximately
100 billion new neutrophils per day. Neutrophils are typically the first cells to arrive at the site of an
infection because there are so many of them in circulation at any given time. ●
Eosinophils: Eosinophils are granulocytes that target multicellular parasites. Eosinophils secrete a range
of highly toxic proteins and free radicals that kill bacteria and parasites. The use of toxic proteins and free
radicals also causes tissue damage during allergic reactions, so activation and toxin release by
eosinophils is highly regulated to prevent any unnecessary tissue damage. While eosinophils only make
up 1-6% of the white blood cells, they are found in many locations, including the thymus, lower
gastrointestinal tract, ovaries, uterus, spleen, and lymph nodes. ●
Basophils: Basophils are also granulocytes that attack multicellular parasites. Basophils release
histamine, much like mast cells. The use of histamine makes basophils and mast cells key players in mounting an allergic response. The Complement System
The complement system (also called the complement cascade) is a mechanism that complements other aspects
of the immune response. Typically, the complement system acts as a part of the innate immune system, but it
can work with the adaptive immune system if necessary.
The complement system is made of a variety of proteins that, when inactive, circulate in the blood. When
activated, these proteins come together to initiate the complement cascade, which starts the following steps: 1. Opsonization 2. Chemotaxis 3. Cell Lysis. 4. Agglutination The adaptive immune system
The adaptive immune system is a subsystem of the overall immune system. It is composed of highly specialized
cells and processes that eliminate specific pathogens and tumor cells. An adaptive immune response is set in
motion by antigens that the immune system recognizes as foreign.
An important function of the adaptive immune system that is not shared by the innate immune system is the
creation of immunological memory or immunity. This occurs after the initial response to a specific pathogen. It
allows a faster, stronger response on subsequent encounters with the same pathogen, usually before the
pathogen can cause symptoms of illness.
Cells of the Innate adaptive System
Lymphocytes are the main cells of the adaptive immune system. They are leukocytes that arise and mature in
organs of the lymphatic system, including the bone marrow and thymus. The human body normally has about 2
trillion lymphocytes, which constitute about a third of all leukocytes. Most of the lymphocytes are normally
sequestered within tissue fluid or organs of the lymphatic system, including the tonsils, spleen, and lymph nodes.
Only about 2% of the lymphocytes are normally circulating in the blood. There are two main types of
lymphocytes involved in adaptive immune responses, called T cells and B cells. T cells destroy infected cells or
release chemicals that regulate immune responses. B cells secrete antibodies that bind with antigens of
pathogens so they can be removed by other immune cells or processes.
There are two categories of lymphocytes, known as B lymphocytes and T lymphocytes. People commonly refer
to these as B cells and T cells. ●
B cells: There are also several types of B cells
Memory B cells circulate in the body to start a fast antibody response when they find a foreign
substance. They remain in the body for decades and become memory cells, which remember antigens
and help the immune system respond faster to future attacks.
Regulatory B cells or Bregs, only account for a small number of B cells in healthy people. Bregs have
protective anti-inflammatory effects in the body and stop lymphocytes that cause inflammation. They also
interact with several other immune cells and promote the production of regulatory T cells, or Tregs.
Plasma cells are terminally differentiated B cells that produce antibodies and are responsible for
antibody-mediated immunity. Terminally differentiated cells are cells that become specialized to a point
after which they can no longer divide. ●
T cells: There are several types of T cells
Killer T cells or cytotoxic, T cells scan the surface of cells in the body to see if they have become
infected with germs or turned cancerous. If so, they kill these cells.
Helper T cells “help” other cells in the immune system to start and control the immune response against
foreign substances. There are different types of helper T cells, and some are more effective than others
against different types of germs.
Regulatory T cells, or Tregs control or suppress other cells in the immune system. They have both
helpful and harmful effects. They maintain tolerance to germs, prevent autoimmune diseases, and limit
inflammatory diseases. But they can also suppress the immune system from doing its job against certain antigens and tumors.
Memory T cells protect the body against antigens that they have previously identified. They live for a
long time after an infection is over, helping the immune system remember previous infections. If the same
germ enters the body a second time, memory T cells remember it and quickly multiply, helping the body fight it more quickly.
Natural killer T cellsare a mixed group of T cells that share characteristics of both T cells and natural
killer cells. They can influence other immune cells and control immune responses against substances in
the body that trigger an immune response.