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ALevel

Biology-9700

The Immune System

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The Immune System

Definition

The system is associated with the defense of the body.

Component of the immune system

The immune system consists of two types of cells that work together to create the defense system.

Phagocytes

These are the cells that are associated with engulfing and destroying the pathogen.

Lymphocytes

Lymphocytes are cells that get activated after the pathogen attaches to their cell surface membrane.

Phagocytes

There are two types of phagocytes. Neutrophils and monocytes. These cells are formed in the bone marrow by the division of precursor cells.

The precursor cell belongs to the myeloid lineage.

Monocytes are present inside the blood in an inactivated form. They leave the blood to the site of infection. Once they are activated they form mature cells called macrophages. These macrophages engulf the pathogen by endocytosis and destroy them.

Neutrophils also work in the same form. They are present in large amount in blood and lives only for a few days.

Lymphocytes

There are two types of lymphocytes i.e B lymphocyte and T lymphocyte. They both are formed from the same precursor cell that arises from lymphoid lineage. After they are formed B lymphocytes settle in the nodes throughout the body while T lymphocytes are settled in the thymus.

Both of the lymphocytes have receptors on their surface. These receptors bind with the pathogen to activated the lymphocytes.

Maturation

During maturation, those lymphocytes which react with their proteins are destroyed.

Antigen

Any particle the immune system fails to recognize is called an antigen. It can be a protein or glycogen molecule that is present inside the structure of bacteria or viruses. These antigens start the immune reaction.

Self-Antigen

These are proteins or particles that are present inside the body of the individual itself but the immune system fails to recognize it. Thus, it initiates an immune response against its antigen.

Role Of T Lymphocytes

There are two types of T lymphocytes helper t cells and killer t cells.  

T Helper Cells

When a pathogen enters the body with the antigen that binds with the receptor T helper cells are activated. after activation, these cells under clonal proliferation ie divide to form a large number of T cells having the same surface receptor.

Half of these cells work to release cytokines( chemicals) that activate other immune cells and initiate the immune response. The remain T helper cells serve as memory cells.

Memory Cells

Memory cells are made after activation of T helper cells by antigen. These cells have a surface receptor that can easily identify the pathogen if it enters the body again. Thus, the second infection with the same pathogen is going to be less damaging than the first as the individual already has immunity against it.

T Killer Cells

Cytotoxic T cells or T killers attaches with the body cells that are showing antigens that bind with the T cell receptor. Thus, they mostly work against intracellular pathogens. The infected cells bear antigen marker signaling T cells.

Role Of B Lymphocytes

B lymphocytes have cell surface receptors. When a pathogen enters the body that matches the receptor it activates the B lymphocytes. These cells then divide to form plasma cells. Plasma cells have a large number of proteins on the surface that can bind with antigen.

Antibodies

After activation plasma cells secrete these proteins in the blood. These are called antibodies. Antibodies bind with the antigen to form the antibody-antigen complex.

They can help the immune system in the following ways:
Neutralize toxins
Covers bacteria and virus and aids in phagocytosis
Prevents them from sticking to tissues.

The remaining plasma cells work as memory cells.

Autoimmune Disorder

The immune system is programmed to differentiate between self-antigens and non-self antigens.

There are times when the immune system fails to do that.

The group of disorders in which immune system attacks its antigen is called an autoimmune disorder.

Example Myasthenia Gravis

In myasthenia gravis, the immune system produces antibodies against acetylcholine receptors present in the postsynaptic neuron. due to these muscles receive fewer signals and becomes weak.

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