The immune system is a network of cells, tissues and organs that work together to defend the body against attacks by foreign invaders. These are primarily tiny infectious disease causing organism such as bacteria and viruses as well as fungi, and parasites.
The immune system is beautifully designed to defend our body’s constitution. It has three layers of defense. Those are the “skins”, the innate and the adaptive arms of the immune system. The innate arm is non-specific. You are born with this one. The adaptive arm, on the other hand, is very specific in its actions and attack.
There are five different types of immune cells that can be classified into two categories. Some have granules and some do not. The immune cells that contain granules include the neutrophils, the eosinophils, and the basophils. The granulocytes, or those cells that do not contain granules, are the lymphocytes and monocytes.
The primary cells of the innate immune system are the monocytes, the neutrophils, the eosinophils and the basophils. The first of those two cells perform a process called phagocytosis to engulf and kill wayward cells in the body.
The lymphocytes are the primary cell of the adaptive arm of the immune system, though they do produce one type of cell that is part of the innate immune complex. These are the NK cells and they are a big player in the internal fight against cancer.
The immune system has a remarkable ability to distinguish between the body’s own cells and a foreign cell. The body’s immune system normally coexists peacefully with cell that carries distinctive self-marker molecules. However, when your immune cell encounter other cells or organism carrying markers that are tagged as foreign, they quickly swing into action to destroy the invader. Anything that can trigger this immune response is called an antigen, and an antigen can be a germ such as any disease-producing agent, like a bacterium or even a tiny piece of a dead pathogenic cell inoculated to stimulate the production of Y shaped antibodies.
All white blood cell, also called leukocytes, are derived from the bone marrow. These cells can be T-cells, B-cell or any of the numerous types of granulocytes that engulf pathogens. A simple knock on the head or a burn on the hand or extremely cold weather or exposure to various forms of radiation, and pathogen can trigger a nonspecific response.