White blood cells
TYPES OF WHITE BLOOD CELLS

There are two main types of leukocyte or white blood cells:

1.   Phagocytes

Phagocytes are white blood cells that can swallow and digest microbes and other foreign particles. Monocytes are phagocytes that circulate in the blood. They are a key component of the innate immune system. There are three main groups of phagocytes: monocytes and macrophages, granulocytes, and dendritic cells. All these three have a slightly different function in the body.

There are several types, including:

  • Neutrophils: Neutrophils are short-lived cells and normally die the following phagocytosis.
  • Monocytes: Monocytes are a type of phagocyte found in the bloodstream. They circulate the body, and when tissue is infected or inflamed they may leave the bloodstream and enter the tissue. 
  • MacrophagesMacrophages are derived from monocytes. They are important cells of the immune system that are formed in response to an infection. Macrophage engulfs and digests cellular debris, foreign substances, microbes, cancer cells. When monocytes migrate into tissues, they develop into macrophages. 
  • Mast Cells: Mast cells are immune cells. A type of white blood cell that is found in connective tissues all through the body. They contain chemicals such as histamine, heparin, cytokines, and growth factors. They release these chemicals during allergic reactions. These are important for healing wounds and defense against infections.

2.   Lymphocytes

Lymphocytes are also a type of White Blood Cells. They are produced from stem cells in the bone marrow and found in the blood and lymph tissue. Lymphocytes can travel throughout the body using blood vessels.

There are two types of Lymphocytes:

  1. B-Lymphocytes: B Lymphocyte, also known as B-cell, is a type of lymphocyte. B-cells fight bacteria and viruses by making Y-shaped proteins called antibodies, which are specific to each pathogen and can lock onto the surface of an invading cell and mark it for destruction by other immune cells.

The role of B lymphocytes

Once B lymphocytes spot the antigen, they begin to secrete antibodies. Each B cell makes one specific antibody. An antigen is any substance that causes your immune system to produce antibodies to fight off disease. Antibodies are part of a large family of chemicals called immunoglobulins, which play many roles in the immune response:

  • Immunoglobulin G (IgG) — marks microbes so other cells can recognize and deal with them.
  • IgM — is an expert at killing bacteria.
  • IgA — concentrates on fluids – tears and saliva, guarding the entrances to the body.
  • IgE — protects against parasites and is responsible for the symptoms of allergy.
  • IgD — remains attached to B lymphocytes, help them to start the immune response.

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.

  1. T-Lymphocytes: T cell is a type of lymphocyte, which develops in the thymus gland. T-Lymphocytes also called T cell and thymocyte. They help protect the body from infection and may help fight cancer. There are two main types of T-cells: helper T-cells and killer T-cells. T cells do not recognize free-floating antigens. Rather, their surfaces contain specialized antibody-like receptors that see antigens on the surfaces of infected cells. T cells contribute to immune defenses.

The role of T Lymphocytes

Helper T-cells stimulate B-cells to make antibodies and help killer cells develop. Killer T-cells directly kill cells that have already been infected by a foreign invader. T-cells also use cytokines as messenger molecules to send chemical instructions to the rest of the immune system to ramp up its response.

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