« The Immune System


The immune system is made up of specialized cells and proteins.

Some of these specialized cells include white blood cells such as lymphocytes (B cells and T cells) and phagocytes (neutrophils, monocytes, and macrophages). White blood cells are produced in the bone marrow. The complement system is a group of proteins found in the blood that are critical in defense against infection. When the immune system is missing any of these parts, people are vulnerable to specific types of diseases.

T Cells

T Cells

T cells are responsible for long-lasting protection against infections. There are four types of T cells, each with a special purpose.

  1. Helper T cells detect infection and get the other cells of the immune system ready for battle. Helper T cells also tell B cells to produce antibodies, highly specialized proteins that help defend the body against infection.
  2. Cytotoxic, or killer, T cells destroy infected cells.
  3. Regulatory T cells tell the immune system when the battle with the pathogens is over and to stop fighting.
  4. Memory T cells remember how to defeat an infection and can respond rapidly if the same infection reoccurs.
B Cells

B Cells

When B cells encounter disease-causing substances, they respond by maturing into plasma cells which produce antibodies. Antibodies are highly specialized proteins in the blood also known as immunoglobulins. Antibodies attach themselves to foreign invaders and mark them for destruction.

There are five main types of antibodies:

  1. IgM antibodies are the first to respond. They offer important protection during the early days of infection. These antibodies tend to stay in the bloodstream where they aid in killing bacteria.
  2. IgG antibodies are the next to respond. These antibodies are formed in large quantities and work in the blood and tissues of the body. They bind to pathogens so that the immune cells have an easier time destroying them. IgG antibodies can pass from a mother to her unborn baby through the placenta.
  3. IgA antibodies are secreted in body fluids such as tears, saliva, and mucus. They protect against infection in the respiratory tract and intestines. These antibodies can pass from mothers to newborns through breast milk.
  4. IgE antibodies are normally present in trace amounts and are important in allergic reactions.
  5. IgD antibodies may be present on the surface of B cells but their function is not fully understood at this time.

Antibodies make pathogens easier to kill by alerting the immune system that the germs need to be destroyed.


Phagocytes are cells that ingest the pathogen by surrounding and digesting it. The main types of phagocytes are neutrophils, monocytes, and macrophages. Macrophages act like scavengers. They look for invading pathogens that have antibodies bound to them and then send alert signals for other macrophages to come and destroy them.

Complement System

The complement system is a group of proteins in the bloodstream that works in an organized fashion to defend against pathogens. These proteins work with antibodies and phagocytes to rid the body of infection.

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