Most important cell in immune system

The main role of the immune system is to protect the body from disease and infection. The immune system is either ‘innate’ (early in life) or ‘adaptive’.

Adaptive immunity is acquired (acquired immunity) after the first few years of life.

The innate immune system is used to protect the body against infections that are not caused by bacteria and viruses. This is the part of the immune system that you can only develop after birth.

The innate immune system recognises threats before the adaptive immune system can develop. This allows the body to respond before it is harmed.

The innate immune system comprises of a series of germ-fighting proteins and cells called leucocytes.

Germ-fighting proteins include the complement system and the phagocytic cells. The phagocytic cells work to engulf and destroy germs (such as bacteria and parasites).

The complement system is an important part of the innate immune system. It works by activating a molecule called a complement protein. This in turn helps to form a protective barrier on the surface of the body to prevent germs from infecting it.

The phagocytic cells are also called macrophages. They work to engulf and destroy germs.

The phagocytic cells are a type of white blood cell. They are responsible for the immune response against germs and bacteria.

White blood cells are a type of immune cell. They help fight infection by destroying germs and damaged cells.

White blood cells are divided into two main types: granulocytes and monocytes.

Granulocytes are responsible for eliminating bacteria and viruses by engulfing and destroying them.

Monocytes are responsible for eliminating other immune cells such as T cells, B cells and NK cells.

The phagocytic cells can also engulf and destroy:

  • Debris such as bacteria and parasites
  • Foreign objects such as glass, plastics and rubber

Germ-fighting proteins

The complement system

The complement system is a part of the innate immune system. It is part of the innate immune system because it recognises germs and bacteria.

The complement system is a system of proteins that are produced by the liver. It has two main components:

  • The C1q component is responsible for activating (turning on) the other complement proteins.
  • The C3 complement protein is responsible for keeping the other complement proteins in a correct state.

The complement system includes many different proteins that are used to help clean up germs, remove damaged cells and fight infection.

The complement proteins are a type of white blood cell. They are present as circulating proteins that are stored in the body. They can be released when the body is in danger or when it has been damaged. They are responsible for binding to germs and destroying them.

Phagocytic cells

The phagocytic cells (macrophages, dendritic cells, neutrophils, etc.) are white blood cells that help eliminate bacteria and damage in the body. They are also known as ‘non-specific cells’ because they are not specific to a single germ or disease.

Each type of phagocytic cell has a different role in the maintenance of the body’s immune system.

Macrophages

Macrophages are a type of white blood cell. They are found in the body’s tissues and are responsible for removing unwanted substances from tissues. They can be found in the liver, spleen, bone marrow and lymph nodes.

Macrophages are responsible for clearing the body’s tissues of debris and dead cells. When this occurs, they are referred to as ‘phagocytosis’.

Dendritic cells

Dendritic cells are a type of white blood cell. They are specialised cells that are responsible for activating T cells (cells that recognise and fight infection).

Dendritic cells are specialised in the lymph system. They are found in lymph nodes, the spleen, thymus and bone marrow.

Dendritic cells are one of the main cells that the immune system uses to activate T cells.

Neutrophils

Neutrophils are responsible for eliminating the body’s tissues of germs and damaged cells. They are commonly found in the bloodstream.

Neutrophils are the first cells to respond to a bacterial or viral infection. They are also responsible for clearing of the blood of damaged cells and foreign objects.

Neutrophils are also known as ‘granulocytes’ because they are responsible for the production of the granules that contain antimicrobial proteins.

Neutrophils can be broken down into two groups:

  • Neutrophilic granulocytes. These cells are responsible for the killing of bacteria and parasites. They are also known as ‘polymorphonuclear neutrophils (PMNs)’.
  • Neutrophilic lymphocytes. These cells are responsible for the killing of other cells (such as T cells). They are also known as ‘lymphocytes’.

Neutrophils are present in the bloodstream, lymph, bone marrow and spleen.

NK cells

NK cells (natural killer cells) are a type of white blood cell. They are specialised in the lymph system and are responsible for killing cells that have been damaged by viruses or bacteria.

NK cells can be broken down into two groups:

  • NK cells. These cells are responsible for the killing of tumour cells. They are also called ‘cytotoxic cells’.
  • NK T cells. These cells are responsible for the killing of other cells in the body. They are also known as ‘cytotoxic T cells’.

NK cells are present in the lymphatic system, bone marrow, lymph nodes and liver.

Lymphocytes

Lymphocytes are a type of white blood cell. They are responsible for attacking and destroying cells infected with viruses or bacteria.

Lymphocytes are responsible for the immune response. The immune response is the body’s natural defence against infection.

Lymphocytes are found in the lymphatic system and bone marrow. They are also found in the bloodstream and lymph nodes.

NK cells are present in the lymphatic system.

T cells

T cells (also known as T-cells) are a type of white blood cell. They specifically recognise and attack specific foreign cells. They are found in the blood, lymph nodes, thymus and bone marrow.

T cells are a type of white blood cell that are a part of the adaptive immune system. They are responsible for attacking the body’s own cells.

T cells recognise and attack the body’s own cells. These attacks are known as ‘clonal anergy’ or ‘apoptosis’.

When a cell is infected with a virus or cancer, the body’s immune system will recognise the foreign cell and mount a defence against it.

In summary

One type of white blood cell is responsible for attacking the body’s own cells, known as ‘phagocytes’.

The phagocytic cell is a type of white blood cell that can be found in the body’s tissues, lymph nodes and bone marrow.

The phagocytic or non-specific white blood cell is also known as a’macrophage’ or ‘neutrophil’.

The phagocytic cell is also known as the ‘complement system’ because it is responsible for binding to and destroying germs.

The other type of white blood cell that is involved in the body’s immune response is known as a ‘T cell’.

The T cell is a type of white blood cell that recognises and attacks the body’s own cells.

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