THE IMMUNE SYSTEM

The immune system is our body’s defense providing us immunity from the external factors that cause illness and disease. Immunity can be subdivided into three categories:

A. Innate immunity: Innate immunity is basic for everyone. Every one of us has this immunity in the form of white blood cells and our protective layers of the body including skin and mucous membranes.

B. Adaptive or acquired immunity: This immunity is developed through exposure to antigens. The antibodies that are formed as a result act as the adaptive immune factors. Vaccines also create adaptive immunity in us.

C. Passive immunity: This type of immunity is generally borrowed from the donor and can vary from person to person. For example, breastfed children have passive immunity as antibodies and immunoglobulin are transferred from the mother to the child through breast milk. But this immunity is not permanent.

So how does the immune system work?

The immune system is a complex system which comprises many activities in the body. The main blood cells that are involved are leukocytes (white blood cells), which are further subdivided into phagocytes (cells that engulf and eat the invading organisms) and lymphocytes (cells that allow the body to remember and identify earlier invaders and help the body to wipe out them). The leukocytes primarily move in the lymphatic system, they reside in lymph nodes and travel between the lymphatic vessels. But they can also migrate and move into the normal blood vessels to provide the optimum immunity.

The lymphocytes are further subdivided into two types: B-lymphocytes and T-lymphocytes (commonly known as B-cells and T-cells). Once an antigen enters our body the B-cells produce antibodies against them; these antibodies are specialized proteins that lock onto specific antigens. Antibodies can also neutralize toxins (poisonous or damaging substances) produced by different organisms. The T-cells are part of the system that destroys antigens that have been tagged by antibodies or cells that have been infected or somehow changed. They act directly on antigens as well as signaling and triggering the phagocytes to engulf and destroy the antigens.

The phagocytes are further subdivided into various other cells, of which neutrophils and macrophages are very important. They engulf the antigens and destroy their cell wall and then engulf them completely.