User:Kinkreet/Immunology/Overview

Immunology is the study of the immune system. It is an important field in searching for treatments for infectious diseases, autoimmune diseases, allergies, transplantations and cancer. It does this by studying why people’s responses to pathogens differ, by designing better vaccines, studying how pathogens is able to bypass the immune system and study how to control immune response.

All immune responses are activated by antigens, which is something that the immune system recognises as foreign and to which the immune system can mount an attack against. Allergies are caused by allergens, a special type of non-parasitic antigen that can stimulate type-I hypersensitivity in an atopic individual. Allergens can take the form of bee venom, proteases in house dust mite faeces, peanuts, grass pollen and many more.

The innate immunity have several essential roles:
 * Recognition of pathogens and discrimination from self
 * Contain the pathogenic substances
 * Control the activation of the adaptive immune response
 * Produce a memory of the pathogen so the response would be more rapid upon secondary infection.

The ability of the immune system to recognize and discriminate against pathogens will increase over time. Firstly, the adaptive immune system of an individual will adapt to mount an attack against cells bearing antigens it has encountered before; as it encounters more and more antigens, its response is improved. Secondly, through the process of natural selection, the population with the best innate immunity are more likely to survive and pass on their innate immunity.

The immune response must be regulated. Overactive response can lead to diseases like asthma, inflammatory bowel disease, atherosclerosis, chronic obstructuve pulmonary disease and rheumatoid artheritis.

Innate Immune Response
The innate immune system respond non-specifically to bacteria, viruses and tumours using cytokines (IFNs, TNFs) to recruit other cells. The cytotoxicity of the innate response are mediated via NK cells, macrophages and Dendritic cells using phagocytosis and oxygen burst, and complement.

Importance
Only when the innate immunity is activated will the adaptive immune response be activated, particularly with respect to T helper 1 (TH1)-cell response.

Diseases caused by defects in the innate immunity are hereditary; the symptoms can appear from birth, or can manifest later in life, either spontaneously, or after infections and injury. Many of these deficiencies stem from deficiencies in the the complement system, as well as in recognition and intracellular pathways.

Hereditary Angioneurotic Edema (HAE)
In the case of type I and II hereditary angioedema (HAE), where the SERPING1 gene is mutated which results in decreased levels (Type I) or dysfunctional C1-inhibitor, one of the inhibitors of the complement system; this leads to an uncontrolled activation of the complement system, and this causes swelling. Hence a person with HAE can appear normal until their first infection, where the complement system is activated but not subsequently deactivated. If HAE occurs in the larynx, it can cause asphyxiation.

Complement factor I deficiency
Complement factor I is a complement protein encoded by the gene CFI; it regulates complement activation by cleaving C3b and C4b, activators of the complement system, which prevents the complement system targeting healthy cells. Deficiencies in CFI lead to the decreased levels of C3, and will reduce the body’s ability to fight off infections, as well as possibly causing an autoimmune response.

N.B. Factor I deficiency can also be referred to as the absence or dysfunction of fibrinogen in blood, which leads to clotting disorders.

Psoriasis
Psoriasis is where the immune system mistakes the skin cells as pathogens and thus dendritic cells sends out signals to induce inflammation (tumor necrosis factor-α, interleukin-1β, and interleukin-6) and to promote proliferation (interleukin-22).

To be incorporated
Eosinophils have half-lives of 30 minutes, and so need to be replaced many times. Neutrophils 6-12 hours. NK cells 6-10 days. Naive lymphocytes 7-20 dats. Memory cells several years.