Systemic lupus erythematosus is a complex disorder that most likely results from a combination of processes and factors.
Environmental factors, such as viruses, exposure to chemicals, or sunlight, trigger inflammatory or immune activity. This immune activation may begin as an appropriate response to an unwanted "invader." But, because of a combination of genetic factors, an individual with lupus develops an ongoing immune response that does not shut itself off appropriately. This leads to waxing and waning flares of inflammation that can involve various organs of the body, depending on specific features of this self-perpetuating immune response in individual patients.
The exact combination of genes that predispose individuals to SLE may differ somewhat from patient to patient, but probably share certain common features which tend to impair the ability of the body to get rid of immune-triggering particles and which tend to prolong or increase the degree of immune responsiveness to these triggers.
A major characteristic of lupus is that it is an autoimmune response in which immune factors, called autoantibodies, attack the person's own cells. Some autoantibodies are normal in a well-balanced immune system, and serve various roles to help the body dispose of wastes, protect from infectious invaders, and to keep blood vessels clear. In healthy people, autoantibodies tend to be well-regulated and well "masked," or covered up, until needed. Therefore, it is probably the high activity and high detestability of autoantibodies that makes lupus unique, not the fact that they exist.
The Normal Immune System Response. The inflammatory process is a byproduct of the activity of the body's immune system, which fights infection and heals wounds and injuries:
The Infection Fighters. B cells and T cells are two important components of the immune system that play a role in the inflammation associated with lupus. Both B cells and T cells belong to a family of immune cells called lymphocytes. Lymphocytes help fight infection.
B cells and T cells are involved in the immune system's response to infection. Antigens are foreign bodies (such as bacteria and viruses) that stimulate the immune system to produce autoantibodies. When a T cell recognizes an antigen it will produce chemicals (cytokines) that cause B cells to multiply and release many immune proteins (antibodies). These antibodies circulate widely in the bloodstream, recognizing the foreign particles and triggering inflammation in order to rid the body of the invasion.
For reasons that are still not completely understood, both the T cells and B cells become overactive in lupus patients. In lupus, a complex interaction between activated immune cells and an impaired antigen-elimination process leads to a greater than normal range of what the antibodies recognize. Eventually, antibodies are made that recognize more of the body's own tissues in a stronger or more persistent manner than is healthy, and inflammatory responses are mounted in these tissues.
Autoantibodies. In the majority of patients with SLE, antinuclear antibodies (ANA) are detectable. Such autoantibodies may be present in individuals up to 7 years prior to their developing symptoms of lupus. Some subtypes of ANA are found in lupus patients and only rarely in people without lupus. These include:
Cytokines. Most immune cells secrete or stimulate the production of powerful immune factors called cytokines. In small amounts, cytokines are indispensable for maintaining the balance of the body during immune responses, including:
If overproduced, however, they can cause serious damage, including dangerous levels of inflammation and cellular injury. Specific cytokines called interferons and interleukins play a critical role in SLE by regulating the secretion of autoantibodies by B cells.
Complement. Another immune factor of high interest in SLE is the complement system. This is comprised of more than 30 proteins and is important for defending and regulating the immune response. Inherited deficiencies in certain complement components (C1q, C1r, C1s, C4, and C2) have long been associated with SLE.
SLE is a complex disorder and researchers are still in the early stages of unraveling how genetic factors may alter and affect the immune system. Researchers estimate that 20 - 100 different genetic factors may make a person susceptible to SLE.
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