Autoimmune disease: why and where it occurs
An autoimmune disease is a condition arising from an abnormal immune response to a functioning body partز At least 80 types of autoimmune diseases have been identified, with some evidence suggesting that there may be more than 100 types Nearly any body part can be involved Common symptoms can be transient and generally include low grade fever and feeling tired.
Autoimmune disease occurs when the body's natural defense system cannot distinguish your own cells from foreign ones, causing the body to mistakenly attack normal cells. There are more than 80 types of autoimmune diseases that affect a wide range of body parts.
Autoimmune disease is controlledby host genes and the environment. Both can increase susceptibility to autoimmunity byaffecting the overall reactivity and quality of the cells of the immune system. Additionally, both control which antigens,and therefore which organs, will be the targets of immuneattack. Antigen/organ specificity is affected by antigen presentation and recognition, antigen expression and the stateand response of the target organs.
An article in the journal nature medicine noted that Autoimmune disease is controlled by properties of the genes of the individual and the environment, both infectious and otherwise, in which the individual exists. The host’s genes affect its susceptibility to autoimmunity at three levels. First, some genes affect the overall reactivity of the immune system and thus can predispose the individual to many different types of autoimmune disease. Second, this altered immunoreactivity is funneled to particular antigens and tissues by other genes that affect T-cell recognition of peptides. Third, still other genes act on the ability of target tissues to modulate immune attack. These last two sets of genes dictate which antigens will be the targets of autoimmunity and hence which organs will be attacked and what damage will occur. In addition, signals from the environment influence the development of autoimmunity at the same three levels, by affecting the overall reactivity of the immune system, antigen-specific response and the state of the potential target tissue. Below, we discuss the evidence for and against each of these ideas.
The environment can also affect the immunoreactivity of the individual by shifting the balance of T cells within the individual between inflammatory, interferon (IFN)-γ–producing Th1 cells and IL-4–and IL-5–producing Th2 cells. Directly or indirectly, bacterial and viral infections usually induce T-cell differentiation into Th1 cells69. Conversely, probably because of the mucosal sites they infect, helminth infections shift the T-cell balance towards Th2 cells70. Autoimmune diseases such as MS, type 1 diabetes and RA involve attack by Th1 cells71. Although Th2-derived cytokines might have some role in lupus, INF-γ and Th1 responses are critical in this antibody-mediated disease as well72. Hence bacterial and certain viral infections, by shifting the T-cell.
This valuable article states in its summary that Our understanding of autoimmune diseases has progressed tremendously in the last 20 years. Even so, much confusion remains, primarily because so many different phenomena affect susceptibility to and precipitation of such illnesses. In our view, both host genes and the environment affect the incidence and type of disease on several fronts: at the levels of the immune response itself, the autoantigen and its presentation, and the target organ. We hope that the expectation that effects can be subdivided in this way will help to clarify what otherwise seem to be the overwhelmingly confusing aspects of these diseases.
Autoimmune diseases form a whole in which we find diseases as different as type 1 diabetes, multiple sclerosis, rheumatoid arthritis or Crohn’s disease. They all correspond to chronic diseases triggered by the body’s loss of immunological tolerance to its own constituents. Immune effectors—antibodies or cells—then cause cellular or tissue lesions that cause more or less severe symptoms. Depending on the nature of these effectors, the lesions affect a particular organ (liver, pancreas, neurons...) or different tissues within the body.
Some very rare autoimmune diseases have a monogenic origin: in this case, the mutation of a single gene is responsible for the pathology, which then most often adopts a severe form. Thus, the mutation of the AIRE gene, which normally intervenes in the central control of autoimmunity in the thymus, can generate an autoimmune polyendocrine syndrome. In the same way, mutations in the FOXP3 gene reduce the level of regulatory T cells and promote the appearance of autoimmune enteropathy type 1 (IPEX syndrome). Autoimmune proliferative syndromes are linked to an anomaly of apoptosis, caused by the mutation of the FAS gene and sometimes the FASL geneز
Expression of AIRE (green) in the human thymus. The AIRE protein (for AutoImmune REgulator) plays a key role in lymphocyte education. However, the molecular and cellular thymic analysis revealed that, from adolescence, girls and women have fewer AEAs than men. The same is true of mice. From puberty, the high level of estrogen in women inhibits the expression of AIRE in the thymus, increasing susceptibility to autoimmune diseases.
An autoimmune disease is a pathology in which the immune system attacks its own constituents. Normally, the immune system is trained to respect the cells in our body. During an autoimmune disease, he turns against them, considering them as foreign. This will create an inflammatory reaction,' explains Professor Zahir Amoura, head of the Internal Medicine Department at Pitié-Salpêtrière, the national reference centre for lupus and other systemic autoimmune diseases.
Myositis, rheumatoid arthritis, myasthenia, multiple sclerosis, type 1 diabetes or Basedow’s disease, autoimmune diseases as a whole would affect 5 to 8% of the population. Very different from each other in their manifestations, yet all result from a malfunction of the immune system and benefit from the progress of a very active research, especially in terms of treatments.
What about the allergies? In allergy, the immune system overreacts to a harmless external element (the allergen): a food, pollen from a tree, mites, nickel, laundry, perfume… This hypersensitivity can occur at any age, including old age.
