How does your body recognize if there is a foreign invader?

Question

this question is related to the inside of your body such as like bacteria ETC

Answer 1

Basically, the immune system is set up to distinguish things which are
foreign to the body from the body itself. In this way, if the body is
invaded by bacteria, viruses, or fungus, the immune system will see the
invader as foreign, and will know to attack it. However, there are a couple of
instances where this isn't totally true. In certain parts of everyone's bodies
there colonies of non-harmful bacteria, which are actually beneficial for the
person. One example is E. Coli bacteria in the intestine which aids the body
in digestion and such. It is not completely clear how the body knows not to
always try to destroy this bacteria, but what seems to be the case is that
the immune system can recognize certain pathogens as non-foreign, and so they
don't get attacked. This phenomenon is called "tolerance".

One idea is that things within the body (foreign or not) have special
chemical and biological "markers" and "tags", which the body will look for to
distinguish which is which. Its a complicated process to determine whether or
not this is the case, so the search is on to recognize what these markers are
and how can we use them. Things like this would be valuable in curing diseases
and infections. Such as cancer or HIV where you might want to give some one a
drug which will seek out the foreign invader and attack it specifically without
attacking the body systems themselves.

Answer 2

A little simpler answer. Your immune system is designed very simular to an army. There are "scout" white blood cells (Monocytes) which are responsible to scan your body. They are designed to capture a piece of the material and bring it to the "general" white blood cell (T-Helper cells). The T-Helper cell then analyzes the proteins that are present. If the protein matches known invaders, the "general" cell then organizes the "soldier" white cells (Neutrophil and Eosinophil) and instructs them how to dissolve and absorb the protein wall and kill either the bacteria or the virus.

There are two other types of white blood cells that fight foreign invaders the B cells produce antibodies that attach themselves (kind of like homing missiles) to the parasite making it easier for the "soldiers" white blood cells to destroy the parasite. The other white blood cell called "Natural Killer Cells" will attack any cell of our body that does not send out a "friendly" signal. Each cell of our body is covered with a protein coat. If this protein coat is not recognized by the NKC then it will attack. This is what causes organ rejection, and if plant or foreign matter enters our body.

The other white blood cell type I didn't mention is called the Basophils type. They are responsible for our allergies.

By the way we do in fact have friendly bacteria in our bodies, but they are only friendly if they are kept in check by our immune system. If they multiply too much, our immune system goes into overdrive and keeps them in check.

Answer 3

sounds like cheating to me.