Health Articles


Written By Dr Steven Gunn (MBChB. BSc. CVIT)


The immune system is our body’s amazing defence system. Our immune system is made up from a number of cells, organs and tissues which produce and store the millions and billions of ‘soldiers’ that is, white blood cells, which protect us from harmful and deadly viruses, bacteria, parasites, fungi, moulds, toxins and allergens which cause debilitating and fatal diseases, infections, toxic cell and organ damage and allergies.

The organs and tissues which manufacture or store the immune system cells include the Bone Marrow, Thymus, Thyroid, Tonsils, Spleen, Appendix, Gut (Peyers Patches and MALT), Lymph nodes and Lymph.


There are 2 main groups of white cells (Leucocytes), namely Phagocytes and Lymphocytes.

  1. Phagocytes consist of Neutrophils, Monocytes, Macrophages and Mast Cells
  • Neutrophils – commonest type and attack mostly bacteria
  • Monocytes – multiple functions
  • Macrophages – attacks pathogens (germs) and remove dying and dead cells and cancer cells
  • Mast cells – Defend against pathogens, allergens and promote healing of wounds
  1. Lymphocytes

Their primary function is to launch a massive attack against harmful micro-organisms and allergens and cancer cells, and especially to remember the invading pathogens and to kill them (especially viruses), if they infect the body again.

Lymphocytes are made in the bone marrow.  Some stay in the bone marrow and develop into B cells (B lymphocytes) and others travel to the thymus gland and become T cells (T lymphocytes).

  • B Cells :     Produce antibodies to kill pathogens and give an individual immunity, as well as to alert the T-cells and promote their action
  • T Cells :     Kill pathogens and cancer cells and alert and enhance the immune system or suppress the immune response

Self versus Non-Self Recognition

The immune system has to be able to recognize which cells and proteins or substances are part of its human body and which are not, so that it does not destroy itself.

Antigens & Immunogens

An antigen or immunogen is any substance, protein or molecule which can cause an immune response or allergic response.  Antigens and immunogens can be pathogens (viruses, bacteria, fungi, moulds, parasites), foreign proteins, pharmaceutical drugs, toxins, chemicals and plant or animal substances.

B Lymphocytes (B Cells)

  • B- cells produce antibodies which are special protein complexes which attack (lock on) to antigens and neutralize or destroy them. For every specific antigen (e.g. virus or bacterium) there is a specific antibody.

Immunoglobulins (Antibodies)

The antibodies consist of a group of chemical compounds called immunoglobulins (Ig).  There are 5 main types:

  • Ig G: Attached to pathogens (e.g. viruses, bacteria) and allows the other immune system cells to come and destroy them.  They remain in the body after the germ or foreign substance has been killed or neutralized.
  • Ig M: These antibodies are the first to bind to the pathogens or foreign invaders such as viruses or bacteria, allowing them to be killed.
  • Ig A: These antibodies are found in fluids like saliva, tears and respiratory secretions and protect the eyes and mouth and respiratory system and mucous membranes.
  • Ig E: These antibodies attach to allergens and parasites and are associated with allergies.
  • Ig D: Attached to the B cells and helps to activate the immune response.

The Antibodies are protein structures which bind to pathogens allowing the White Cells (Leucocytes) and the release of certain chemical processes (The Complement System) to kill the germs.

T Lymphocytes (T Cells)

There are many different types of T cells, also known as CD cells.  Two of the main types are T helper cells and T killer cells

  • T helper cells (Th cells) -  These cells help to stimulate and coordinate the immune system by communicating with other cells in the immune system.
  • T killer cells (Cytotoxic T cells or NK Natural Killer cells) – These cells attack and kill viruses and cancer cells


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