Aetiology and pathology of systemic lupus erythematosus
Systemic lupus erythematosus (SLE) is an autoimmune rheumatic disease characterised by widespread inflammation affecting virtually every organ or system in the body. The disease is associated with the deposition of autoantibodies and immune complexes, leading to tissue damage.
It has a multifactorial aetiology and affects mainly women during the childbearing years. The various factors include genetic, hormonal and environmental components. As in any autoimmune condition, it is believed that the presence of susceptibility genes in a predisposed individual can be triggered by an initial stimulus (probably environmental) which enables a certain critical threshold to be attained, leading to the development of clinical features. This pathway incorporates the perturbation of the immune response involving polyclonal B cell activation and excessive T cell help.
The precise immune disturbances leading to the development of SLE remain unknown, although various clues have been provided by studies of animal models.1 Current research involves attempts to understand the process of production of pathogenic autoantibodies and the roles played by cytokines, adhesion molecules and apoptosis.
The understanding of SLE immunopathology is essential to improving how patients are treated. The treatment methods are non-specific and prone to causing serious side effects. An overview of the factors involved in the aetiopathogenesis of SLE is presented below.
The higher rate of the disease seen in monozygotic twins (25 per cent) compared with dizygotic twins (3 per cent), the increased frequency of lupus and other immunological disorders in relatives of lupus patients compared with healthy controls,and the higher prevalence of SLE in certain ethnic groups, leads to the suggestion that genetic factors play a role in the pathogenesis of SLE.
Recent studies have shown that there is a complex genetic trait to the susceptibility of this disorder, with contributions from themajor histocompatibility complex (MHC) genes and many other genes, which regulate apoptosis (see below), cytokines, immunoglobulin production and antigen presentation. Genetic complexity in polygenic diseases is mostly related to the low penetrance of each contributing gene, that is, to the increase in probability of disease expression given a particular allele.2
The ethnic background in SLE shows a bias, with more Afro-Caribbeans (1:250) being affected than Orientals (1:1000) and Caucasians (1:4300). The black race is an independent risk factor for developing SLE. African-Americans and Afro-Caribbeans living in the United States and the United Kingdom have the greatest risk of developing SLE. They also develop the disease earlier in life, and have an increased frequency and severity of renal pathology. Also of note and not satisfactorily explained, is the fact that SLE is rare in native Africans.3 A study in Birmingham demonstrated major differences in the incidence and prevalence rates of SLE in the UK depending on ethnic group. The observed prevalence in females was 206:100,000 among Afro-Caribbeans, 91:100,000 among Asians and 36:100,000 among Caucasians. These results were irrespective of place of birth.4
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Citation: Hospital Pharmacist URI: 10974280
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