A human or animal must defend itself against multitude of different pathogens including viruses, bacteria, fungi, and protozoan and metazoan parasites as well as tumours and a number of various harmful agents which are capable to derange its homeostasis. For this, a plenty of effector mechanisms capable of defending the body against such antigens and agents have developed and these can be mediated by soluble molecules or by cells. If infection occur as a consequence of the tissue damage, the innate and, later, the adaptive immune systems are triggered to destroy the infectious agent.
Inflammation is a complex stereotypical reaction of the body expressing the response to damage of its cells and vascularized tissues. In avascular tissues, e.g. in normal cornea, the true inflammation does not occure.
The discovery of the detailed processes of inflammation has revealed a close relationship between inflammation and the immune response.
The five basic symptoms of inflammation - redness (rubor), swelling (tumour), heat (calor), pain (dolor) and deranged function (functio laesa) have been known since the ancient Greek and Roman era. These signs are due to extravasation of plasma and infiltration of leukocytes into the site of inflammation. Early investigators considered inflammation a primary host defence system. From this point of view inflammation is the key reaction of the innate immune response but in fact, inflammation is more than this, since it can lead to death, as in anaphylactic shock, or debilitating diseases, as in arthritis and gout.
According to different criteria, inflammatory responses can be divided into several categories. The criteria include:
