Antibodies or immunoglobulin, as they are known, are the defending molecules of the body against any kind of external aggression by pathogenic microorganisms and parasites.
These are manufactured by specific cells called lymphocytes and circulate in the blood. Antibodies confer resistance to extra-cellular pathogenic organisms and the soluble poisonous substances (toxins) produced by them. The antibody manufacturing lymphocytes are only a part of a complex system of vertebrates known as immune system.
The immune system of a vertebrate is even more complex than an advanced military of a country. The response of this system against any kind of external aggression is known as immune response / immunity. Immunity is of two primary types: (1) natural / innate (inborn) / non-adaptive and (2) acquired / adaptive.
This is a broad spectrum defense mechanism raised against all types of aggressions. This is present right from the birth, therefore, also referred to as ‘inborn’.
The same type of response is mounted to counter all pathogenic organisms. The elements and the mechanism of action of this system pre-exist the invasion of the foreign agent. It is not specific for a particular type of organism. Therefore!, it is also known as non-specific host defense.
The non-specific responses together constitute the ‘first line of defense’ of the body. It has the following properties: (1) quick initiation, (2) broad based action (low specificity) and (3) no memory.