Neutrophils are granular white blood cells. It is an active phagocytic cell. Neutrophils arrive at the infected site within 30 minutes of receiving the signal from the infected site. Opsonin substances in neutrophils recognize pathogens. The proteolytic enzymes of neutrophils then rapidly destroy the bacteria. A neutrophil can ingest 3-20 bacteria. After ingestion of microbes, neutrophils die and are excreted as pus.

Neutrophils secrete special chemicals. These chemicals stimulate monocytes and macrophages to eat bacteria. The chemical increases the rate of the phagocytosis process.

1. Enzymes of Lalars: Lalars contain lysozyme enzyme. This enzyme destroys bacteria.
2. Pancreatic enzymes: Protease enzymes secreted by the pancreas destroy bacteria and fungi.
3. Mucous enzymes: Lactoperoxide and lysozyme enzymes secreted from the mucous membrane of alimentary canal and trachea act as bactericides.
4. Bile: Bile contains bile. This bile destroys the bacteria.
5. Stomach acid: Hydrochloric acid secreted from the stomach wall destroys the bacteria in the food.

The skin is the body’s first line of defense. It acts as the first barrier against germs.

1. Carotenoid coat: The skin forms the carotenoid coat in the body. Germs cannot enter the body through this membrane.
2. Histiocyte: When the skin is cut or torn, the histiocyte cells come out and destroy the germs in the wound.
3. Secretion of sweat and oil glands: Sweat and oily substances accumulate on the skin. These substances increase the pH. High pH kills bacteria.
4. Acids and metabolic wastes: Bacteria accumulate acids and metabolic wastes on the skin. Bacteria cannot multiply due to these acids and metabolic wastes.
5. Lysozyme: The skin contains an enzyme called lysozyme. This enzyme destroys the bacterial wall.
6. Cerumen: Cerumen is a waxy substance known as ear wax. It is secreted from ceruminous glands. It resists bacteria, fungi and insects.
7. Ultraviolet rays: The skin protects the body from the ultraviolet rays of the sun.

The immune system that destroys specific pathogens that enter the body is remembered for life and responds quickly and effectively to any subsequent attack is called the third layer of defense. Lymphocyte cells produce antibodies that destroy bacterial antigens. It is the best, active, powerful and permanent defense system. This defense system is:

1. Detects and targets foreign microbes. Separates healthy cells from diseased and dead cells.
2. Kills specific germs and keeps them in memory and prevents attacks from those germs for years.
3. The immune system can be effective in any part of the body and protects the whole body.

When macrophages attack viruses, bacteria and foreign objects, pyrogens are released from the cells. Pyrogens cause rise in body temperature and fever. Germs cannot multiply at high temperatures. The immune system of the body increases.

Release antigens after entering the microbial cells. Cytokines are released from cells to destroy bacterial antigens. Cytokines stimulate the body’s immune system.

When a wound occurs in any part of the body, the molecule quickly prevents blood clotting and closes the wound. As a result, germs cannot enter the wound.

In the attack of bacteria, the wound of the cells becomes red, hot, swollen and painful. This is called inflammation or response. Histamine is released when a cell is attacked by bacteria. Histamine causes numerous pores in the capillary tube. Macrophages, neutrophils etc. enter the cell through these pores and consume microbes, toxins and dead cells.

Complement system is a group of 20 types of plasma proteins. These proteins remain inactive and are later converted into active proteins. Activating proteins induce specific and non-specific defense mechanisms. The complement system always helps cells such as NK cells, neutrophils, macrophages, etc. to destroy pathogens.

Interferon is a high molecular weight glycoprotein. It is produced by virus-infected cells and prevents the virus from multiplying. This interferon attaches to the membranes of other healthy cells and helps those cells produce new interferons. In this way, the body builds a protective wall.