An autoimmune disease is a condition arising from an abnormal immune response to a normal body part. There are at least 80 types of autoimmune diseases. Nearly any body part can be involved. Common symptoms include low grade fever and feeling tired. Often symptoms come and go.

Autoimmunity is the system of immune responses of an organism against its own healthy cells and tissues. Any disease that results from such an aberrant immune response is termed an "autoimmune disease". Prominent examples include celiac disease, diabetes mellitus type 1, sarcoidosis, systemic lupus erythematosus (SLE), Sjögren's syndrome, eosinophilic granulomatosis with polyangiitis, Hashimoto's thyroiditis, Graves' disease, idiopathic thrombocytopenic purpura, Addison's disease, rheumatoid arthritis (RA), ankylosing spondylitis, polymyositis (PM), dermatomyositis (DM) and multiple sclerosis (MS). Autoimmune diseases are very often treated with steroids.

The hallmark symptom of SS is a generalized dryness, typically including dry mouth and keratoconjunctivitis sicca (dry eyes), part of what are known as sicca ("dryness") symptoms. Sicca syndrome also incorporates vaginal dryness and chronic bronchitis. SS may cause skin, nose, and vaginal dryness, and may affect other organs of the body, including the muscles (myositis), kidneys, blood vessels, lungs, liver, biliary system, pancreas, peripheral nervous system (distal axonal neuropathy or small fiber peripheral neuropathy) and brain. Some people have gastrointestinal or esophageal diseases such as GERD, achlorhydria or gastroparesis. Chronic pain with accompanying fatigue and brain fog may also occur.

Skin dryness in some people with SS may be the result of lymphocytic infiltration into skin glands. The symptoms may develop insidiously, with the diagnosis often not considered for several years, because the complaints of sicca may be otherwise attributed to medications, a dry environment, aging, or may be regarded as not of severity warranting the level of investigation necessary to establish the presence of the specific underlying autoimmune disorder.

SS can damage vital organs of the body with symptoms that may plateau or worsen, or go into remission as with other autoimmune diseases. Some people may experience only the mild symptoms of dry eyes and mouth, while others have symptoms of severe disease. Many patients can treat problems symptomatically. Others are forced to cope with blurred vision, constant eye discomfort, recurrent mouth infections, swollen parotid glands, dysphonia (vocal disorders including hoarseness), and difficulty in swallowing and eating. Debilitating fatigue and joint pain can seriously impair quality of life. Some patients can develop renal (kidney) involvement (autoimmune tubulointerstitial nephritis) leading to proteinuria (excess protein in urine), urinary concentrating defect, and distal renal tubular acidosis.

An autoimmune disease is a condition arising from an abnormal immune response to a normal body part. There are at least 80 types of autoimmune diseases. Nearly any body part can be involved. Common symptoms include low grade fever and feeling tired. Often symptoms come and go.

The cause is generally unknown. Some autoimmune diseases such as lupus run in families, and certain cases may be triggered by infections or other environmental factors. Some common diseases that are generally considered autoimmune include celiac disease, diabetes mellitus type 1, Graves' disease, inflammatory bowel disease, multiple sclerosis, psoriasis, rheumatoid arthritis, and systemic lupus erythematosus. The diagnosis can be difficult to determine.

Treatment depends on the type and severity of the condition. Nonsteroidal anti-inflammatory drugs (NSAIDs) and immunosuppressants are often used. Intravenous Immunoglobulin may also occasionally be used. While treatment usually improves symptoms they do not typically cure the disease.

About 24 million (7%) people in the United States are affected by an autoimmune disease. Women are more commonly affected than men. Often they start during adulthood. The first autoimmune diseases were described in the early 1900s.

An immune disorder is a dysfunction of the immune system. These disorders can be characterized in several different ways:

- By the component(s) of the immune system affected

- By whether the immune system is overactive or underactive

- By whether the condition is congenital or acquired

According to the International Union of Immunological Societies, more than 150 primary immunodeficiency diseases (PIDs) have been characterized. However, the number of acquired immunodeficiencies exceeds the number of PIDs.

It has been suggested that most people have at least one primary immunodeficiency. Due to redundancies in the immune system, though, many of these are never detected.

SS is associated with a number of other medical conditions, many of which are autoimmune or rheumatic disorders, such as celiac disease, fibromyalgia, SLE (lupus), autoimmune thyroiditis, multiple sclerosis and spondyloarthropathy, and several malignancies, principally non-Hodgkin lymphoma.

For a disease to be regarded as an autoimmune disease it needs to answer to "Witebsky's postulates" (first formulated by Ernest Witebsky and colleagues in 1957 and modified in 1994):

- Direct evidence from transfer of disease-causing antibody or disease-causing T lymphocyte white blood cells

- Indirect evidence based on reproduction of the autoimmune disease in experimental animals

- Circumstantial evidence from clinical clues

- Genetic evidence suggesting "clustering" with other autoimmune diseases

In the classical sense, acute graft-versus-host-disease is characterized by selective damage to the liver, skin (rash), mucosa, and the gastrointestinal tract. Newer research indicates that other graft-versus-host-disease target organs include the immune system (the hematopoietic system, e.g., the bone marrow and the thymus) itself, and the lungs in the form of immune-mediated pneumonitis. Biomarkers can be used to identify specific causes of GvHD, such as elafin in the skin. Chronic graft-versus-host-disease also attacks the above organs, but over its long-term course can also cause damage to the connective tissue and exocrine glands.

Acute GvHD of the GI tract can result in severe intestinal inflammation, sloughing of the mucosal membrane, severe diarrhea, abdominal pain, nausea, and vomiting. This is typically diagnosed via intestinal biopsy. Liver GvHD is measured by the bilirubin level in acute patients. Skin GvHD results in a diffuse red maculopapular rash, sometimes in a lacy pattern.

Mucosal damage to the vagina can result in severe pain and scarring, and appears in both acute and chronic GvHD. This can result in an inability to have sexual intercourse.

Acute GvHD is staged as follows: overall grade (skin-liver-gut) with each organ staged individually from a low of 1 to a high of 4. Patients with grade IV GvHD usually have a poor prognosis. If the GvHD is severe and requires intense immunosuppression involving steroids and additional agents to get under control, the patient may develop severe infections as a result of the immunosuppression and may die of infection.

In the oral cavity, chronic graft-versus-host-disease manifests as lichen planus with a higher risk of malignant transformation to oral squamous cell carcinoma in comparison to the classical oral lichen planus. Graft-versus-host-disease-associated oral cancer may have more aggressive behavior with poorer prognosis, when compared to oral cancer in non-hematopoietic stem cell transplantation patients.

In the clinical setting, graft-versus-host-disease is divided into acute and chronic forms, and scored or graded on the basis of the tissue affected and the severity of the reaction.

- The "acute" or "fulminant" form of the disease (aGvHD) is normally observed within the first 100 days post-transplant, and is a major challenge to transplants owing to associated morbidity and mortality.

- The "chronic" form of graft-versus-host-disease (cGvHD) normally occurs after 100 days. The appearance of moderate to severe cases of cGVHD adversely influences long-term survival.

Currently, there are no reliable molecular markers reflecting the onset or clinical course of aGVHD. However, it has been shown that genes responsible for cytokine signaling, inflammatory response, and regulation of cell cycle are differentially expressed in patients with fatal GvHD versus "indolent" GvHD.

Autoimmune diseases can be broadly divided into systemic and organ-specific or localised autoimmune disorders, depending on the principal clinico-pathologic features of each disease.

- Systemic autoimmune diseases include SLE, Sjögren's syndrome, sarcoidosis, scleroderma, rheumatoid arthritis, cryoglobulinemic vasculitis, and dermatomyositis. These conditions tend to be associated with autoantibodies to antigens which are not tissue specific. Thus although polymyositis is more or less tissue specific in presentation, it may be included in this group because the autoantigens are often ubiquitous t-RNA synthetases.

- Local syndromes which affect a specific organ or tissue:

- Endocrinologic: Diabetes mellitus type 1, Hashimoto's thyroiditis, Addison's disease

- Gastrointestinal: Coeliac disease, Crohn's disease, Pernicious anaemia

- Dermatologic: Pemphigus vulgaris, Vitiligo

- Haematologic: Autoimmune haemolytic anaemia, Idiopathic thrombocytopenic purpura

- Neurological: Multiple sclerosis, Myasthenia gravis, Encephalitis

Using the traditional “organ specific” and “non-organ specific” classification scheme, many diseases have been lumped together under the autoimmune disease umbrella. However, many chronic inflammatory human disorders lack the telltale associations of B and T cell driven immunopathology. In the last decade it has been firmly established that tissue "inflammation against self" does not necessarily rely on abnormal T and B cell responses.

This has led to the recent proposal that the spectrum of autoimmunity should be viewed along an “immunological disease continuum,” with classical autoimmune diseases at one extreme and diseases driven by the innate immune system at the other extreme. Within this scheme, the full spectrum of autoimmunity can be included. Many common human autoimmune diseases can be seen to have a substantial innate immune mediated immunopathology using this new scheme. This new classification scheme has implications for understanding disease mechanisms and for therapy development.

The signs and symptoms of Kikuchi disease are fever, enlargement of the lymph nodes (lymphadenopathy), skin rashes, and headache. Rarely, enlargement of the liver and spleen and nervous system involvement resembling meningitis are seen. Often a bout of extreme fatigue can occur - often taking hold during latter parts of the day and the affected person can be more prone to fatigue from exercise.

Insulitis is an inflammation of the islets of Langerhans, a collection of endocrine tissue located in the pancreas. The islets containing the pancreatic β-cells, and in some cases, the exocrine tissues, become infiltrated by T and B lymphocytes, macrophages and dendritic cells. This innate immune cell and lymphocyte infiltration can result in destruction of the insulin producing beta cells of the islets, and clinical diabetes. Insulitis is often studied in the multiple low dose streptozotocin (MLDS) mouse model or the non-obese diabetic (NOD) mouse model of type 1 diabetes. The chemokine family of proteins may play a key role in promoting leukocytic infiltration into the pancreas prior to pancreatic beta-cell destruction.

The regulatory T cells (Tregs ), formerly known as suppressor T cells, are a subpopulation of T cells that modulate the immune system, maintain tolerance to self-antigens, and prevent autoimmune disease. Tregs are immunosuppressive and generally suppress or downregulate induction and proliferation of effector T cells. Tregs express the biomarkers CD4, FOXP3, and CD25 and are thought to be derived from the same lineage as naïve CD4 cells. Because effector T cells also express CD4 and CD25, Tregs are very difficult to effectively discern from effector CD4+, making them difficult to study. Recent research has found that the cytokine TGFβ is essential for Tregs to differentiate from naïve CD4+ cells and is important in maintaining Treg homeostasis.

Mouse models have suggested that modulation of Tregs can treat autoimmune disease and cancer and can facilitate organ transplantation. Their implications for cancer are complicated. Tregs tend to be upregulated in individuals with cancer, and they seem to be recruited to the site of many tumors. Studies in both humans and animal models have implicated that high numbers of Tregs in the tumor microenvironment is indicative of a poor prognosis, and Tregs are thought to suppress tumor immunity, thus hindering the body's innate ability to control the growth of cancerous cells. Recent immunotherapy research is studying how regulation of T cells could possibly be utilized in the treatment of cancer.

The classic symptoms of coeliac disease include pale, loose, and greasy stool (steatorrhoea) and weight loss or failure to gain weight. More common symptoms are subtle or primarily occur in organs other than the bowel itself. It is also possible to have coeliac disease without any classic symptoms whatsoever. This represents at least 43% of the cases in children. Many adults with subtle disease only have fatigue or anaemia.

Autoimmune hepatitis, formerly called lupoid hepatitis, is a chronic, autoimmune disease of the liver that occurs when the body's immune system attacks liver cells causing the liver to be inflamed. Common initial symptoms include fatigue or muscle aches or signs of acute liver inflammation including fever, jaundice, and right upper quadrant abdominal pain. Individuals with autoimmune hepatitis often have no initial symptoms and the disease is detected by abnormal liver function tests.

Anomalous presentation of MHC class II receptors on the surface of liver cells, possibly due to genetic predisposition or acute liver infection, causes a cell-mediated immune response against the body's own liver, resulting in autoimmune hepatitis. This abnormal immune response results in inflammation of the liver, which can lead to further symptoms and complications such as fatigue and cirrhosis. The disease may occur in any ethnic group and at any age, but is most often diagnosed in patients between age 40 and 50.

Autoimmune hepatitis may present completely asymptomatic (12–35% of the cases), with signs of chronic liver disease, or acute or even fulminant hepatic failure.

People usually present with one or more nonspecific symptoms, sometimes of long lasting duration, as fatigue, general ill health, lethargy, weight loss, mild right upper quadrant pain, malaise, anorexia, nausea, jaundice or arthralgia affecting the small joints. Rarely, rash or unexplained fever may appear. In women, amenorrhoea is a frequent feature. Physical examination may be normal, but it may also reveal signs and symptoms of chronic liver disease. Many people have only laboratory abnormalities as their initial presentation, as unexplained increase in transaminases and are diagnosed during an evaluation for other reasons. Others have already developed cirrhosis at diagnosis.

Autoimmune hepatitis frequently appears associated with other autoimmune conditions, mainly celiac disease, vasculitis, and autoimmune thyroiditis.

Kikuchi disease or Kikuchi-Fujimoto disease was described in 1972 in Japan. It is also known as histiocytic necrotizing lymphadenitis, Kikuchi necrotizing lymphadenitis, phagocytic necrotizing lymphadenitis, subacute necrotizing lymphadenitis, and necrotizing lymphadenitis.

It was first described by Dr Masahiro Kikuchi (1935–2012) in 1972 and independently by Y. Fujimoto.

Coeliac disease, also spelled celiac disease, is a long-term autoimmune disorder primarily affecting the small intestine that occurs in people who are genetically predisposed. Classic symptoms include gastrointestinal problems such as chronic diarrhoea, abdominal distention, malabsorption, loss of appetite, and among children failure to grow normally. This often begins between six months and two years of age. Non-classic symptoms are more common, especially in people older than two years. There may be mild or absent gastrointestinal symptoms, a wide number of symptoms involving any part of the body, or no obvious symptoms. Coeliac disease was first described in childhood; however, it may develop at any age. It is associated with other autoimmune diseases, such as diabetes mellitus type 1 and thyroiditis, among others.

Coeliac disease is caused by a reaction to gluten, which are various proteins found in wheat and in other grains such as barley, and rye. Moderate quantities of oats, free of contamination with other gluten-containing grains, are usually tolerated. The occurrence of problems may depend on the variety of oat. Upon exposure to gluten, an abnormal immune response may lead to the production of several different autoantibodies that can affect a number of different organs. In the small-bowel this causes an inflammatory reaction and may produce shortening of the villi lining the small intestine (villous atrophy). This affects the absorption of nutrients, frequently leading to anaemia.

Diagnosis is typically made by a combination of blood antibody tests and intestinal biopsies, helped by specific genetic testing. Making the diagnosis is not always straightforward. Frequently, the autoantibodies in the blood are negative and many people have only minor intestinal changes with normal villi. People may have severe symptoms and be investigated for years before a diagnosis is achieved. Increasingly, the diagnosis is being made in people without symptoms as a result of screening. Evidence regarding the effects of screening, however, is not sufficient to determine its usefulness. While the disease is caused by a permanent intolerance to wheat proteins, it is not a form of wheat allergy.

The only known effective treatment is a strict lifelong gluten-free diet, which leads to recovery of the intestinal mucosa, improves symptoms, and reduces risk of developing complications in most people. If untreated, it may result in cancers such as intestinal lymphoma and a slight increased risk of early death. Rates vary between different regions of the world, from as few as 1 in 300 to as many as 1 in 40, with an average of between 1 in 100 and 1 in 170 people. In developed countries, it is estimated that 80% of cases remain undiagnosed, usually because of minimal or absent gastrointestinal complaints and poor awareness of the condition. Coeliac disease is slightly more common in women than in men. The term "coeliac" is from the Greek κοιλιακός ("koiliakós", "abdominal") and was introduced in the 19th century in a translation of what is generally regarded as an ancient Greek description of the disease by Aretaeus of Cappadocia.

All people with ALPS have signs of lymphoproliferation, which makes it the most common clinical manifestation of the disease. The increased proliferation of lymphoid cells can cause the size of lymphoid organs such as the lymph nodes and spleen to increase (lymphadenopathy and splenomegaly, present in respectively over 90% and over 80% of patients). The liver is enlarged (hepatomegaly in 30 - 40% of patients).

Autoimmune disease is the second most common clinical manifestation and one that most often requires treatment. Autoimmune cytopenias: Most common. Can be mild to very severe. Can be intermittent or chronic. These include: Autoimmune hemolytic anemia, Autoimmune neutropenia, Autoimmune thrombocytopenia.

Other signs can affect organ systems similar to systemic lupus erythematosus (least common, affecting <5% of patients) Symptoms of the nervous system include: Autoimmune cerebellar ataxia; Guillain–Barré syndrome; transverse myelitis. Gastrointestinal signs like Autoimmune esophagitis, gastritis, colitis, hepatitis, pancreatitis can be found or (Dermatologic) Urticaria, (Pulmonary) bronchiolitis obliterans, (Renal) Autoimmune glomerulonephritis, nephrotic syndrome.

Another sign are cancers such as Hodgkin and non-Hodgkin lymphomas which appear to be increased, possibly due to Epstein–Barr virus-encoded RNA-positivity. Some carcinomas may occur. Unaffected family members with genetic mutations are also at an increased risk of developing cancer.

Immunodeficiency (or immune deficiency) is a state in which the immune system's ability to fight infectious disease and cancer is compromised or entirely absent. Most cases of immunodeficiency are acquired ("secondary") due to extrinsic factors that affect the patient's immune system. Examples of these extrinsic factors include HIV infection, extremes of age, and environmental factors, such as nutrition. In the clinical setting, the immunosuppression by some drugs, such as steroids, can be either an adverse effect or the intended purpose of the treatment. Examples of such use is in organ transplant surgery as an anti-rejection measure and in patients suffering from an overactive immune system, as in autoimmune diseases. Some people are born with intrinsic defects in their immune system, or primary immunodeficiency. A person who has an immunodeficiency of any kind is said to be immunocompromised. An immunocompromised person may be particularly vulnerable to opportunistic infections, in addition to normal infections that could affect everyone. Immunodeficiency also decreases cancer immunosurveillance, in which the immune system scans the body's cells and kills neoplastic ones.

Some of the symptoms and signs of IPEX syndrome are the following:

AGID is diagnosed with a complete medical history, exam of patients motility and with special blood tests looking for autoantibodies consistent with neurologic autoimmunity. Blood tests included evaluations of immunofluorescence (neuronal nuclear and cytoplasmic antibodies), radioimmunoprecipitation assays (neuronal and muscle plasma membrane cation channel antibodies), and enzyme-linked immunosorbent assay (muscle striational antibodies). A finding, along with medical history, of ganglionic neuronal acetylcholine receptor and N-type voltage-gated calcium channel autoantibodies in the blood stream would result in a medically acceptable diagnosis of AGID.

Often AGID is a symptom of other problems, including colon cancer, lupus, lung, breast, or ovarian carcinoma or thymoma. or other diseases. Irritable bowel syndrome (IBS) is the most recognized form of AGID.

Autoimmune retinopathy (AIR) is a rare disease in which the patient's immune system attacks proteins in the retina, leading to loss of eyesight. The disease is poorly understood, but may be the result of cancer or cancer chemotherapy. The disease is an autoimmune condition characterized by vision loss, blind spots, and visual field abnormalities. It can be divided into cancer-associated retinopathy (CAR) and melanoma-associated retinopathy (MAR). The condition is associated with retinal degeneration caused by autoimmune antibodies recognizing retinal proteins as antigens and targeting them. AIR's prevalence is extremely rare, with CAR being more common than MAR. It is more commonly diagnosed in females (approximately 60% of diagnosed patients are females) in the age range of 50-60.

Cryoglobulinemia, cryoglobulinaemia, or cryoglobulinemic disease, is a medical condition in which the blood contains large amounts of cryoglobulins – proteins (mostly immunoglobulins themselves) that become insoluble at reduced temperatures. This should be contrasted with cold agglutinins, which cause agglutination of red blood cells.

Cryoglobulins typically precipitate at temperatures below normal body temperatureand will dissolve again if the blood is heated. The precipitated clump can block blood vessels and cause toes and fingers to become gangrenous. While this disease is commonly referred to as cryoglobulinemia in the medical literature, it is better termed cryoglobulinemic disease for two reasons: 1) cryoglobulinemia is also used to indicate the circulation of (usually low levels of) cryoglobulins in the absence of any symptoms or disease and 2) healthy individuals can develop transient asymptomatic cryoglobulinemia following certain infections.

In contrast to these benign instances of circulating cryoglobulins, cryoglobulinemic disease involves the signs and symptoms of precipitating cryoglobulins and is commonly associated with various pre-malignant, malignant, infectious, or autoimmune diseases that are the underlying cause for production of the cryoglobulins.