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What is the function of the immune system?

The immune system performs specific defense against strange or harmful agents (antigens) to the body. Antigens are often in contact with the skin or entering the airway, the digestive tube and the genital orifices and mucosae. They can also penetrate the circulation directly through wounds.

What are the two groups of defense mechanisms of the body against strange or harmful agents? What is the difference between them?

The body has many defense mechanisms against strange pathogenic agents. These mechanisms are divided into two groups: the specific mechanisms and the unspecific mechanisms. The specific mechanisms are part of the immune system and comprehend the humoral immune response and the cellular immune response that respectively produce antibodies and defense cells against specific antigens. The unspecific mechanisms fight in general manner any type of antigen (they do not have specificity) and in them a series of defense means are included, like the skin barrier against strange agents, the mucous and ciliated epithelium of the airway, inflammation (the inflammatory response) and the action of unspecific proteins and defense cells (e.g., interferons and macrophages).

What is inflammation?

Inflammation is the initial response of the unspecific defense system versus aggressions against the body (the aggressions may be caused by infectious parasites, chemical contamination, trauma, physical agents like heat and fire, autoimmunity, etc.). During inflammation a series of unspecific leukocytes present in the circulation is attracted to the injury site in an attempt to destroy harmful agents and to isolate the affected region of the tissue.