The nonspecific immunity or innate immunity is a type of non-specific immunity present at birth, or in people whose immune systems are not yet fully developed, and therefore, it is not able to provide specific and selective pathogens. It is also known as natural, hereditary or constitutive immunity and it is the first line of defence in non-immunized organisms. This first line of defence of the organism's defence system is recognized as the oldest response and it is common to all multicellular organisms, including insects and plants.

The innate immune system includes lymphocytes NK (Natural Killer), mast cells, eosinophils, basophils, macrophages, neutrophils and dendritic cells: these cells have, between them, very different working mechanisms, but they are all able to eliminate and/or to identify pathogens.

What is nonspecific or innate immunity?

The mechanisms of natural immunity are pre-existing at the point of contact with microorganisms and they are activated in a timely manner by the presence of pathogens before the body is able to develop a specific immune response towards them (specific immunity).

This first line of defence depends on anatomical barriers, physiological barriers, and mechanisms of endocytosis/phagocytosis as well as inflammatory barriers.

The anatomical barriers consist of the skin and mucous membranes of the human organism, structured to defend the body and prevent the entry of most pathogens.

The physiological barriers include: temperature (many microorganisms do not survive or overcome certain temperatures), pH levels (for example, gastric acidity is a physiological barrier in the innate immunity to infections because very few microorganisms are able, once ingested, to survive the low pH levels present in the stomach), and various soluble factors (including soluble lysozyme proteins, interferon and complement, which are able to bind to neighbouring cells and stimulate a state of generalized antiviral resistance).

Endocytosis is a generic term that indicates the ability of cells to capture the extracellular material that surrounds them. Phagocytosis is a type of specialized ingestion endocytosis, which consists of extracellular particles including pathogenic microorganisms.

The inflammatory barriers are activated as a result of chemical signals emitted by the cells attacked by the pathogen. They represent one of the first defence mechanisms of the body in the presence of a harmful agent.

Moreover, the process of phagocytosis begins with the specialized immune cells called macrophages that fight pathogens. The macrophages are cells that patrol the body through the blood stream ensuring the absence of pathogens. Once a pathogen invades the body, the macrophages move into the tissue to swallow the pathogen and digest it in order to destroy it. Additionally, basophils are cells that secrete histamines, which signal more immune cells about the threat, while the natural killer T cells look find cells that do not resemble host cells and release chemicals that break down and destroy the pathogens.

What function does the nonspecific or innate immunity serve?

Innate immunity is the first line of defence in people whose immune system has not yet fully developed or it is underdeveloped. It represents the first response of the organism in terms of preventing infections. The mechanisms of innate immunity are often used to eliminate pathogens even in the context of specific immune responses.