By recognizing self from non-self. Every cell in the body carries specific protein markers that are recognized by all immune cells so they do not attack self, at least when the system is operating well.
Most cells of the body have self markers on the surface of their cell called the major histocompatibility complex (MHC). The MHC allows cells of the immune system to recognize the cell as part of our self.
They have the same genetic structure as the rest of your body, it will only target foreign cells.
The medical term for the immune system failing to recognize its own body tissue and attacking its owner's body is autoimmunity. Common examples of autoimmune disorder are (a) Rheumatoid arthritis and (b) systemic lupus erythematosus ("lupus")
The immune system will target the body's own cells
This happens to my Mom sometimes. When she's really stressed, tired, sick, etc; her immune system starts attacking her body again. I don't know why, it just does. It happened with her immune system or something like that and also her eyes. The immune System needs to know what is friendly and a threat to the brain & body. Although it has trouble sometimes when you get a transplant and the shape/size/composition/etc isn't similar enough to your own.
1. Your immune system can recognize cells based on the proteins present on the surface of cells. Viruses, bacteria, and other foreign cells are recognized as being different from your own cells and are attacked by your immune system.
Also. Allied the innate immune system, cells and proteins involved recognize structures shared by classes of microbes not present on the body's own cells and can also recognize molecules released by infected, damaged, or dead cells. The innate system can eliminate microbes on its own but more commonly cells of the innate immune system release chemokines to attract cells that are involved in the adaptive immune system to initiate an antigen or microbe specific immune response
Your immune system attacking your own body.
The body's immune system is able to distinguish between self and non-self cells through various mechanisms. One such mechanism is the presence of major histocompatibility complex (MHC) molecules on the surface of cells, which helps the immune system recognize self-cells. Non-self cells, such as infected or cancerous cells, may display abnormal proteins or antigens that are recognized as foreign by the immune system, prompting an immune response to attack and eliminate them.
Class I and II MHC molecules are what the body uses to recognize it's own cells as "self". If it detects an antigen (anything foreign to the body) the immune system will trigger a response.
An illness that occurs when the body tissues are attacked by its own immune system.
Your body's immune system had antibodies that fight against the bacteria or virus infecting you.
The body's immune system normally fights off infections by releasing white blood cells into the blood to isolate and destroy the germs. This results in inflammation (swelling and redness) of the body tissues in that area. The immune system responds like this to anything in the blood it doesn't recognize, and dies down when the infection has been cleared. It is thought that sarcoidosis happens because the immune system has gone into "overdrive", where the body starts to attack its own tissues and organs. The resulting inflammation then causes granulomas to develop in the organs.
Think about it for a second. If you lead an army into battle, and your own army start to shoot each other, what odds do you have of winning against the oposition? If the body starts to kill it's own cells that may be used to kill pathogens, it is immediately weakened