The Immune System

Your body's defense system

                                                                    The Basics

In your body there is a mechanism designed to defend you from millions of bacteria, microbes, viruses, toxins and parasites. It is made up of different organs, cells and proteins and aside from the nervous system, it is the most complex system that the human body has.How does the immune system work?

The immune system is the body's defense against infectious organisms and other invaders. Through a series of steps called the immune response, the immune system attacks organisms and substances that invade body systems and cause disease.

The immune system is made up of a network of cells, tissues, and organs that work together to protect the body. The cells involved are white blood cells, or leukocytes, which come in two basic types that combine to seek out and destroy disease-causing organisms or substances.

Your immune system uses a huge army of defender cells - different types of white blood cell. You make about 1000 million of them every day in your bone marrow. Some of these cells, called macrophages, constantly patrol your body, destroying germs as soon as they enter. This is your 'natural' or inborn immunity. But if an infection begins to take hold, your body fights back with an even more powerful defence of T- and B-cells. They give you acquired immunity, so that the same germ can never make you as ill again.How does your immune system work?

                                                             The Components

The two basic types of leukocytes are:

  1. phagocytes, cells that chew up invading organisms
  2. lymphocytes, cells that allow the body to remember and recognize previous invaders and help the body destroy them

A number of different cells are considered phagocytes. The most common type is the neutrophil, which primarily fights bacteria. If doctors are worried about a bacterial infection, they might order a blood test to see if a patient has an increased number of neutrophils triggered by the infection. Other types of phagocytes have their own jobs to make sure that the body responds appropriately to a specific type of invader.

The two kinds of lymphocytes are B lymphocytes and T lymphocytes. Lymphocytes start out in the bone marrow and either stay there and mature into B cells, or they leave for the thymus gland, where they mature into T cells. B lymphocytes and T lymphocytes have separate functions: B lymphocytes are like the body's military intelligence system, seeking out their targets and sending defenses to lock onto them. T cells are like the soldiers, destroying the invaders that the intelligence system has identified.

Leukocytes are produced or stored in many locations in the body, including the thymus, spleen, and bone marrow. For this reason, they're called the lymphoid organs. There are also clumps of lymphoid tissue throughout the body, primarily as lymph nodes, that house the leukocytes.

The leukocytes circulate through the body between the organs and nodes via lymphatic vessels and blood vessels. In this way, the immune system works in a coordinated manner to monitor the body for germs or substances that might cause problems.

Immune SystemAlthough antibodies can recognize an antigen and lock onto it, they are not capable of destroying it without help. That's the job of the T cells, which are part of the system that destroys antigens that have been tagged by antibodies or cells that have been infected or somehow changed. (Some T cells are actually called "killer cells.") T cells also are involved in helping signal other cells (like phagocytes) to do their jobs.

Antibodies also can neutralize toxins (poisonous or damaging substances) produced by different organisms. Lastly, antibodies can activate a group of proteins called complement that are also part of the immune system. Complement assists in killing bacteria, viruses, or infected cells.

White blood cells destroy invading pathogens. Unlike red blood cells, white blood cells can move out of the blood vessels and  "patrol" all the tissues of the body. Some of these cells attack pathogens directly. A macrophage is a white blood cell that destroy pathogens by engulfing and digesting them. Macrophages help start the body's immune response to antigens. An antigen is a substance that stimulates a response by the  immune system. An antigen can be a pathogen or any foreign material in the body.

Your external defense is also an important part of your immune system. Your skin is an exter defense and it protects pathogens that may enter your body. Your skin also has structures, such as hair, nails, and sweat and oil glands, the help provide protection. For example, glands in your skin secrete oil that can kill pathogens. Mucus and saliva in your mouth wash pathogens downd into your stomache where they are quickly digested. Hair such as eyelashes and ear hair keep many pathogens from entering your body. Nails protect your fingertips and toes. The skin and all of these structures make up the integumentary system.


Macrophages- attacks pathogens and other invaders

T cell- coordinates the immune system and attacks many infected cells

B cell- makes antibodies

Skin- keeps pathogens from entering your body

                                                       Here's how it works:

When the macrophages recognize viruses they activate helper T cells and also engulf  the virus particles. The helper T cells activate B cells and killer T cells.The activated B cell creates antibodies that attach to a specific  antigen. The killer T cells destroy infected cells to prevent the antigens from spreading.

The response to pathogens is orchestrated by the complex interactions and activities of the large number of diverse celTl types involved in the immune response. The innate immune response is the first line of defense and occurs soon after pathogen exposure. It is carried out by phagocytic cells such as neutrophils and macrophages, cytotoxic natural killer (NK) cells, and granulocytes. The subsequent adaptive immune response includes antigen-specific defense mechanisms and may take days to develop. Cell types with critical roles in adaptive immunity are antigen-presenting cells including macrophages and dendritic cells. Antigen-dependent stimulation of various cell types including T cell subsets, B cells, and macrophages all play critical roles in host defense.Cells of the Immune System

When antigens (foreign substances that invade the body) are detected, several types of cells work together to recognize them and respond. These cells trigger the B lymphocytes to produce antibodies, specialized proteins that lock onto specific antigens.

Once produced, these antibodies continue to exist in a person's body, so that if the same antigen is presented to the immune system again, the antibodies are already there to do their job. So if someone gets sick with a certain disease, like chickenpox, that person typically doesn't get sick from it again.

This is also how immunizations prevent certain diseases. An immunization introduces the body to an antigen in a way that doesn't make someone sick, but does allow the body to produce antibodies that will then protect the person from future attack by the germ or substance that produces that particular disease.

All of these specialized cells and parts of the immune system offer the body protection against disease. This protection is called immunity.

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