Our Immune System – Innate and Adaptive Immunity

Immune System

  • The immune system has a vital role: It protects your body from harmful substances, germs and cell changes that could make you ill. It is made up of various organs, cells and proteins.
  • The immune system is spread throughout the body and involves many types of cells, organs, proteins, and tissues. Crucially, it can distinguish our tissue from foreign tissue — self from non-self. Dead and faulty cells are also recognized and cleared away by the immune system.

The main tasks of the body’s immune system are

  • to fight disease-causing germs (pathogens) like bacteria, viruses, parasites or fungi, and to remove them from the body,
  • to recognize and neutralize harmful substances from the environment, and
  • to fight disease-causing changes in the body, such as cancer cells.

White blood cells

They are also called leukocytes. White blood cells are on constant patrol and looking for pathogens. When they find a target, they begin to multiply and send signals out to other cell types to do the same.

Our white blood cells are stored in different places in the body, which are referred to as lymphoid organs. These include the following:

  • Thymus — a gland between the lungs and just below the neck.
  • Spleen — an organ that filters the blood. It sits in the upper left of the abdomen.
  • Bone marrow — found in the center of the bones, it also produces red blood cells.
  • Lymph nodes —small glands positioned throughout the body, linked by lymphatic vessels.

There are two main types of leukocytes

Phagocytes

These cells surround and absorb pathogens and break them down, effectively eating them. There are several types, including:

  • Neutrophils normally make up the largest number of circulating WBCs. They move into an area of damaged or infected tissue, where they engulf and destroy bacteria or sometimes fungi.
  • Monocytes , similar to neutrophils, move to an area of infection and engulf and destroy bacteria. They are associated more often with long-term (chronic) rather than acute infections. They are also involved in tissue repair and other functions involving the immune system.
  • Eosinophils respond to infections caused by parasites, play a role in allergic reactions (hypersensitivities), and control the extent of immune responses and inflammation.
  • Basophils usually make up the fewest number of circulating WBCs and are thought to be involved in allergic reactions.
  • Macrophages — these patrol for pathogens and also remove dead and dying cells.
  • Mast cells — they have many jobs, including helping to heal wounds and defend against pathogens.

Lymphocytes

Lymphocytes help the body to remember previous invaders and recognize them if they come back to attack again.

Lymphocytes begin their life in bone marrow. Some stay in the marrow and develop into B lymphocytes (B cells), others head to the thymus and become T lymphocytes (T cells). These two cell types have different roles:

  • B lymphocytes — they produce antibodies and help alert the T lymphocytes.
  • T lymphocytes — they destroy compromised cells in the body and help alert other leukocytes.

Antigen (Antibody Generator)

The immune system needs to be able to tell self from non-self. It does this by detecting proteins that are found on the surface of all cells. It learns to ignore its own or self proteins at an early stage.

An antigen is any substance that can spark an immune response.

In many cases, an antigen is a bacterium, fungus, virus, toxin, or foreign body. But it can also be one of our own cells that is faulty or dead.

Once B lymphocytes spot the antigen, they begin to secrete antibodies (antigen is short for “antibody generators”). Antibodies are special proteins that lock on to specific antigens. Antibodies lock onto the antigen, but they do not kill it, only mark it for death. The killing is the job of other cells, such as phagocytes.

Innate immunity

Innate immunity refers to nonspecific defense mechanisms that come into play immediately or within hours of an antigen’s appearance in the body. These mechanisms include physical barriers such as skin, chemicals in the blood, and immune system cells like Phagocytes that attack foreign cells in the body. The innate immune response is activated by chemical properties of the antigen.

Adaptive immunity

Adaptive immunity refers to antigen-specific immune response. The adaptive immune response is more complex than the innate. The antigen first must be processed and recognized. Once an antigen has been recognized, the adaptive immune system creates an army of immune cells specifically designed to attack that antigen. Adaptive immunity also includes a “memory” that makes future responses against a specific antigen more efficient.

Killer T cells (cytotoxic T lymphocytes) — as the name suggests, these T cells attack other cells. They are particularly useful for fighting viruses. They work by recognizing small parts of the virus on the outside of infected cells and destroy the infected cells.

Helper T cells (Th cells) — they coordinate the immune response. Some communicate with other cells, and some stimulate B cells to produce more antibodies. Others attract more T cells or cell-eating phagocytes.

~Praveen Jada

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