Mechanisms Associated with Autoimmune Disease

Complement system. A group of serum proteins with the capacity to interact with each other when activated. The chain reaction of the activated complement components results in formation of a lytic complex and several biologically active peptides of low molecular weight (anaphylatoxins). The system can be activated by antigen-antibody complexes (classical pathway) and by other components, e.g. bacteria (alternative pathway). As an effector mechanism of the humoral immune response, the activated complement system facilitates opsonization, phagocytosis, and lysis of cellular antigens. Some defects in components of complement are associated with autoimmune diseases (see complement deficiency). 

The mechanism most commonly invoked to explain the association of infection with autoimmune disease is molecular mimicry that is, the concept that antigens (or more properly, epitopes) of the microorganism closely resemble self-antigens.50 The induction of an immune response to the microbial antigen thus results in cross-reactivity with selfantigens and the induction of autoimmunity. Although epitope specific cross-reactivity has been shown in some animal models,48,51 53 molecular mimicry is clearly demonstrated to be the causative mechanism in few, if any, human diseases.3 54,55... 

Acquired von Willebrand disease is a rare bleeding disorder that is similar to the congenital form of the disease. It has been reported primarily in association with autoimmune disorders, such as systemic lupus erythematosus, lymphoproliferative disorders, and neoplastic disease. Certain medications also have been associated with acquired von Willebrand disease, including valproic acid, dextran, and ciprofloxacin. Bleeding manifestations vary frommild to severe, and the condition often resolves with treatment of the underlying disease. In the acquired disease, von Wfllebrand factor appears to be synthesized in normal amounts, but then is rapidly removed from plasma by anti-von Willebrand factor antibodies, adsorption to tumor cells, or other mechanisms. ... 

The function of the ALD protein is not fully understood, and knockout mice lacking it do not exhibit the severe CNS neurological deficits commonly associated with the human disease despite a similar accumulation of VLCFAs [26], Furthermore, the clinical variability in human patients cannot be accounted for by the severity of the biochemical abnormality or the nature of the gene defect. These observations, plus other data from mice with defects in VLCFA metabolism, raise the issue of whether the accumulation of VLCFAs in myelin is crucial to the pathological mechanisms or is an epiphenomenon. Unlike most other lipid-storage diseases, active ALD brain lesions are characterized by perivascular accumulation of lymphocytes. For this reason, it has been hypothesized that the severity of CNS pathology may relate to an autoimmune reaction that varies from patient to patient and... 

Other causes of gastric atrophy, such as those due to Helicobacter pylori,AIDS, or radiation injury, can lead to a similar outcome but from different pathogenic mechanisms. Therefore, vitamin B12 deficiency, resulting in neurological, psychiatric, metabolic, and hematological disorders, can arise from any one of the many causes listed in Table 28-1. For this reason, the term pernicious anemia (PA) is used here to describe only the classical disease that is associated with IF deficiency due to autoimmune gastritis. 

Autoimmune diseases have been reported to be more frequent in human subjects treated with several recombinant cytokines [38], For instance, increased titers or the new occurrence of autoantibodies have been observed in hepatitis C patients treated with the recombinant interferons-alpha (IFNa). Quite a few clinical case reports describe the development of organ-specific as well as systemic autoimmune diseases including systemic lupus erythematosus, insulin-dependent type I diabetes mellitus, autoimmune thrombocytopenia, autoimmune hemolytic anemia, myasthenia gravis, and autoimmune thyroiditis in patients under IFNa therapy. Although the mechanism involved is not fully elucidated, the available data support the pathogenic potential of IFNa in autoimmunity [31]. In contrast, autoimmune effects associated with IFNp therapy are thought to be of lesser concern based on the current clinical evidence [38], Thyroid autoimmunity in contrast to other autoimmune diseases is frequent in patients treated with recombinant interleukin-2 (rIL-2). Thus, among 281 previously euthyroid cancer patients treated with rIL-2, up to 41%... 

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