2. Specific Immunity to infection – the regulatory arm
Do we need exposure to harmful germs to build tolerance to harmless antigens?
Agents such as pollen, dust mites, certain foods etc can act as antigens and induce an immune response.
- Allergic diseases such as asthma, eczema and food allergies occur when the body overreacts to antigens such as pollen, dust mites etc causing inflammatory responses such as sneezing, constriction of airways etc and irritation.
- Autoimmune diseases such as Type 1 diabetes, multiple sclerosis etc occur when the immune system overreacts against the body’s own cells and tissues (self antigens). This triggers production of antibodies or inflammatory agents against the body’s own cells, causing tissue injury and degradation, typical of autoimmune disease.
The process by which the body prevents itself from attacking its own cells is called Immune tolerance.
Regulation of immune responses by exposure to Old Friends (OF)
Acquired immunity is vital to protect against infectious disease, but these immune responses are potentially dangerous if they are not properly regulated, as happens in those who develop allergies and autoimmune diseases
Preventing inappropriate immune responses, is brought about by regulatory T lymphocytes (Treg cells) which down regulate allergic and autoimmune reactions, thereby avoiding development of allergic and autoimmune diseases.
In normal humans, T cell secretion that suppress allergic and autoimmune responses is driven, not by exposure to harmful germs, but exposure to Old Friends microbiota (commensal microbiota and environmental microbes). In the absence of stimuli from OFs, Treg cells are no longer adequately induced causing increased susceptibility to “overreaction” leading to allergic and autoimmune diseases.
Over time the body has evolved to distinguish antigens of disease-causing microbes that need to be eliminated, from antigens of the OF microbes that need to be tolerated, but which are still recognised by the immune system and interact with it to drive the Treg responses which prevent allergies and autoimmune disease.