Cells Of Immune System


Phagocytosis describes “eating up” substance; therefore, phagocytes are any cell types that act via this mechanism. The phagocytes consist of granulocytes, macrophages, and dendrites cells.

Granulocytes: The granulocytes are often the first on the scene of an invasion and are programmed to directly kill invaders, often continuing until they themselves die off. Pus in a wound is largely made up of dead granulocytes. Granulocytes are also called polymorphonuclear leukocytes and consists of three cell types: neutrophils, eosinophils, and basophils. Their action occurs primarily via enzyme activity and is directed at parasites and bacteria. Mast cells are similar; they stay put in mucosa or connective tissue and don’t have the ability to move around. What they can do, though, is let loose the secretory granules that they carry. These granules contains inflammatory chemicals, like histamine, prostaglandins, and leukotrienes, which cause inflammation to both kill invaders and send an alert message to the rest of the system. This activity is important in the allergic response and some autoimmune conditions.

Macrophage: Macrophages start out as monocytes in the blood. When an invasion occurs, the monocytes transform into macrophages, which go into the tissue where the invaders is and begin engulfing it. They move more slowly than granulocytes but live longer and get more done while they live. In addition to directly killing invaders, macrophages stimulate other parts of the immune system by presenting the antibodies associated with that invader, as a dendrites does.

Dendritic cells: Dendritic cells (also known as dendrites) are also part of the phagocytes; they not only directly eat up invading organisms, but they also have the ability to stimulate the rest of the immune system. When dendrites engulf an invader, they place part of that organism’s genetic material on their surface. This process is called antigen presentation. It’s this presentation that stimulates T and B cells to join the attack.


Lymphocytes are category of cells that include B cells and T cells. These cells are born in the bone marrow but travel to other tissues for maturation, in preparation for their work in the immune system. Each of these cells becomes specialized to recognize only one kind of antigen; the receptors on their surfaces will bind with only one kind of molecule.

T cells are divided into helper T cells and killer T cells. The helper T cells become activated when a macrophage or dendritic cell presents an antigen on its surface from an organism that it just engulfed. If that antigen happens to be the one that T cell is programmed to respond to, the cell becomes activated, rapidly dividing as well as making further chemicals to stimulate other T cells and B cells to promote the immune response. Killer T cells, however, are designed to roam the body looking for invaders. If they recognize as being a problem, like bacteria or cancer cells, they kill it.

B cells roam the body looking for things that match the receptors that are on their surface/ After they run across these invaders, a triggering signal is set off, a protein from helper T cells is added, and the B cells begin to divide. In this process from helper T cells is added, and the B cells begin to divide. In this process, they differentiate into plasma cells and memory cells.

  • Plasma cells produce a protein called an antibody that is formed rapidly and attaches to the intruding organism. These antibodies make it easier for the remaining immune cells to identify the intruding organism and kill it. Antibodies can attach to more than one organism at at time, in effect gathering the intruders into groups for more efficient processing by the other cells.
  • Memory cells are produced in a similar fashion. They have the ability to make antibodies but have a much longer life span than a plasma cell. They function to respond to a similar infection much more rapidly in the future. This means that the first time one is infected by an organism, the system is often at its slowest; future infections are attended to much more rapidly due to the activity of memory cells.

How they work?

Overall, the different cells work to activate a response and promptly the activity of all the other cells. The granulocytes and macrophages respond first, causing inflammation and damage to the invading organisms, which not only kills some of the organisms but also sends the signal that something is up. The dendrites arrive and eat some of the organisms, too. The macrophages and dendrites can then present the antigens they just ate up to the T cells, creating helper and killer T cells as well as B cell activation. After the B cells are activated, they create antibodies, which not only contribute to killing off the invading organism but also create future immunity to that organism.

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