Autoimmunity Health Dictionary

An antibody (see ANTIBODIES) produced by a person’s immune system (see IMMUNITY) that acts against the body’s own tissues, resulting in AUTOIMMUNITY.... autoantibody

A group of diseases affecting CONNECTIVE TISSUE. The term is really outdated since there is no evidence that collagen is primarily involved. Fibrinoid NECROSIS and VASCULITIS are two ‘characteristics’, and autoimmunity reaction may occur in the connective tissue. The latter affects blood vessels and causes secondary damage in the connective tissue. Such conditions are sometimes described as collagen vascular diseases, examples being RHEUMATOID ARTHRITIS, SYSTEMIC LUPUS ERYTHEMATOSUS (SLE), and SCLERODERMA.... collagen diseases

Exophthalmos, or PROPTOSIS, refers to forward displacement of the eyeball and must be distinguished from retraction of the eyelids, which causes an illusion of exophthalmos. Lid retraction usually results from activation of the autonomic nervous sytem. Exophthalmos is a more serious disorder caused by in?ammatory and in?ltrative changes in the retro-orbital tissues and is essentially a feature of Graves’ disease, though it has been described in chronic thyroiditis (see THYROID GLAND, DISEASES OF). Exophthalmos commonly starts shortly after the development of thyrotoxicosis but may occur months or even years after hyperthyroidism has been successfully treated. The degree of exophthalmos is not correlated with the severity of hyperthyroidism even when their onset is simultaneous. Some of the worst examples of endocrine exophthalmos occur in the euthyroid state and may appear in patients who have never had thyrotoxicosis; this disorder is named ophthalmic Graves’ disease. The exophthalmos of Graves’ disease is due to autoimmunity (see IMMUNITY). Antibodies to surface antigens on the eye muscles are produced and this causes an in?ammatory reaction in the muscle and retroorbital tissues.

Exophthalmos may also occur as a result of OEDEMA, injury, cavernous venous THROMBOSIS or a tumour at the back of the eye, pushing the eyeball forwards. In this situation it is always unilateral.... exophthalmos

A condition in which the whole of the THYROID GLAND is di?usely enlarged and ?rm. It is one of the diseases produced by AUTOIMMUNITY. The enlargement is due to di?use in?ltration of lymphocytes and increase of ?brous tissue. This form of GOITRE appears in middle-aged women, does not give rise to symptoms of thyrotoxicosis (see THYROID GLAND, DISEASES OF – Thyrotoxicosis), and tends to produce myxoedema (see THYROID GLAND, DISEASES OF – Hypothyroidism).... hashimoto’s disease

The study of immune responses to the environment. Its main clinical applications include improving resistance to microbial infections (see IMMUNITY), combating the effects of impaired immunity (see IMMUNODEFICIENCY), controlling harmful immune reactions (see ALLERGY), and manipulating immune responses (see IMMUNOTHERAPY) to prevent harmful immunological responses such as graft rejection and autoimmune diseases (see AUTOIMMUNITY). The clinical study of disordered immunity now forms the allied discipline of clinical immunology, which is closely linked to the laboratory-based discipline of immunopathology.... immunology

The manipulation of IMMUNITY by immunological (see IMMUNOLOGY) means to reduce harmful reactions or to boost bene?cial responses. Severe ALLERGY to wasp or bee stings is often treated by a course of injections with allergen puri?ed from insect venom. There are current attempts to treat autoimmune diseases (see AUTOIMMUNITY) with monoclonal antibodies to the T-cell populations or cytokines implicated in the immunopathogenesis of the disorder.

Strategies are also being evaluated for treating cancer by boosting the patient’s own immunity to cancer cells. One approach is immunisation with cancer cells manipulated in vivo to increase a T-lymphocyte attack on antigens expressed by tumour cells. Another method is to manipulate the cytokine network into encouraging an immune attack on, or self-destruction (‘apoptosis’) of, malignant cells.

Immunotherapy is however a developing science, and its place in the routine treatment of immunological and malignant diseases is still evolving.... immunotherapy

menopause occurring before the age of 40. It may be caused by autoimmunity, chemotherapy, radiotherapy, or genetic factors, for example a mutation in the FSH receptor gene causing excess secretion of gonadotrophins and small underdeveloped ovaries. Treatment is by hormone replacement, either with the contraceptive pill or HRT. *Oocyte donation should be discussed if the patient wishes for assisted conception.... premature ovarian failure

n. inflammation of the thyroid gland. Acute thyroiditis is due to bacterial infection, and subacute (or de Quervain’s) thyroiditis is caused by a viral infection. Chronic thyroiditis is commonly caused by an abnormal immune response (see autoimmunity) in which lymphocytes invade the tissues of the gland. See Hashimoto’s disease.... thyroiditis

The body’s defence against foreign substances such as bacteria, viruses and parasites. Immunity also protects against drugs, toxins and cancer cells. It is partly non-speci?c – that is, it does not depend on previous exposure to the foreign substance. For example, micro-organisms are engulfed and inactivated by polymorphonuclear LEUCOCYTES as a ?rst line of defence before speci?c immunity has developed.

Acquired immunity depends upon the immune system recognising a substance as foreign the ?rst time it is encountered, storing this information so that it can mount a reaction the next time the substance enters the body. This is the usual outcome of natural infection or prophylactic IMMUNISATION. What happens is that memory of the initiating ANTIGEN persists in selected lymphocytes (see LYMPHOCYTE). Further challenge with the same antigen stimulates an accelerated, more vigorous secondary response by both T- and B-lymphocytes (see below). Priming the immune system in this manner forms the physiological basis for immunisation programmes.

Foreign substances which can provoke an immune response are termed ‘antigens’. They are usually proteins but smaller molecules such as drugs and chemicals can also induce an immune response. Proteins are taken up and processed by specialised cells called ‘antigenpresenting cells’, strategically sited where microbial infection may enter the body. The complex protein molecules are broken down into short amino-acid chains (peptides – see PEPTIDE) and transported to the cell surface where they are presented by structures called HLA antigens (see HLA SYSTEM).

Foreign peptides presented by human leucocyte antigen (HLA) molecules are recognised by cells called T-lymphocytes. These originate in the bone marrow and migrate to the THYMUS GLAND where they are educated to distinguish between foreign peptides, which elicit a primary immune response, and self-antigens (that is, constituents of the person themselves) which do not. Non-responsiveness to self-antigens is termed ‘tolerance’ (see AUTOIMMUNITY). Each population or clone of T-cells is uniquely responsive to a single peptide sequence because it expresses a surface molecule (‘receptor’) which ?ts only that peptide. The responsive T-cell clone induces a speci?c response in other T-and B-lymphocyte populations. For example, CYTOTOXIC T-cells penetrate infected tissues and kill cells which express peptides derived from invading micro-organisms, thereby helping to eliminate the infection.

B-lymphocytes secrete ANTIBODIES which are collectively termed IMMUNOGLOBULINS (Ig)

– see also GAMMA-GLOBULIN. Each B-cell population (clone) secretes antibody uniquely speci?c for antigens encountered in the blood, extracellular space, and the LUMEN of organs such as the respiratory passages and gastrointestinal tract.

Antibodies belong to di?erent Ig classes; IgM antibodies are synthesised initially, followed by smaller and therefore more penetrative IgG molecules. IgA antibodies are adapted to cross the surfaces of mucosal tissues so that they can adhere to organisms in the gut, upper and lower respiratory passages, thereby preventing their attachment to the mucosal surface. IgE antibodies also contribute to mucosal defence but are implicated in many allergic reactions (see ALLERGY).

Antibodies are composed of constant portions, which distinguish antibodies of di?erent class; and variable portions, which confer unique antigen-binding properties on the product of each B-cell clone. In order to match the vast range of antigens that the immune system has to combat, the variable portions are synthesised under the instructions of a large number of encoding GENES whose products are assembled to make the ?nal antibody. The antibody produced by a single B-cell clone is called a monoclonal antibody; these are now synthesised and used for diagnostic tests and in treating certain diseases.

Populations of lymphocytes with di?erent functions, and other cells engaged in immune responses, carry distinctive protein markers. By convention these are classi?ed and enumerated by their ‘CD’ markers, using monoclonal antibodies speci?c for each marker.

Immune responses are in?uenced by cytokines which function as HORMONES acting over a short range to accelerate the activation and proliferation of other cell populations contributing to the immune response. Speci?c immune responses collaborate with nonspeci?c defence mechanisms. These include the COMPLEMENT SYSTEM, a protein-cascade reaction designed to eliminate antigens neutralised by antibodies and to recruit cell populations which kill micro-organisms.... immunity

A serious disorder in which the chief symptoms are muscular weakness and a special tendency for fatigue to come on rapidly when e?orts are made. The prevalence is around 1 in 30,000. Two-thirds of the patients are women, in whom it develops in early adult life. In men it tends to develop later in life.

It is a classical example of an autoimmune disease (see AUTOIMMUNITY). The body develops ANTIBODIES which interfere with the working of the nerve endings in muscle that are acted on by ACETYLCHOLINE. It is acetylcholine that transmits the nerve impulses to muscles: if this transmission cannot be e?ected, as in myasthenia gravis, then the muscles are unable to contract. Not only the voluntary muscles, but those connected with the acts of swallowing, breathing, and the like, become progressively weaker. Rest and avoidance of undue exertion are necessary, and regular doses of neostigmine bromide, or pyridostigmine, at intervals enable the muscles to be used and in some cases have a curative e?ect. These drugs act by inhibiting the action of cholinesterase – an ENZYME produced in the body which destroys any excess of acetylcholine. In this way they increase the amount of available acetylcholine which compensates for the deleterious e?ect of antibodies on the nerve endings.

The THYMUS GLAND plays the major part in the cause of myasthenia gravis, possibly by being the source of the original acetylcholine receptors to which the antibodies are being formed. Thymectomy (removal of the thymus) is often used in the management of patients with myasthenia gravis. The incidence of remission following thymectomy increases with the number of years after the operation. Complete remission or substantial improvement can be expected in 80 per cent of patients.

The other important aspect in the management of patients with myasthenia gravis is IMMUNOSUPPRESSION. Drugs are now available that suppress antibody production and so reduce the concentration of antibodies to the acetylcholine receptor. The problem is that they not only suppress abnormal antibody production, but also suppress normal antibody production. The main groups of immunosuppressive drugs used in myasthenia gravis are the CORTICOSTEROIDS and AZATHIOPRINE. Improvement following steroids may take several weeks and an initial deterioration is often found during the ?rst week or ten days of treatment. Azathioprine is also e?ective in producing clinical improvement and reducing the antibodies to acetylcholine receptors. These effects occur more slowly than with steroids, and the mean time for an azathioprine remission is nine months.

The Myasthenia Gravis Association, which provides advice and help to sufferers, was created and is supported by myasthenics, their families and friends.... myasthenia gravis

n. a reduction in the quantity of the oxygen-carrying pigment *haemoglobin in the blood. The main symptoms are excessive tiredness and fatigability, breathlessness on exertion, pallor, and poor resistance to infection.

There are many causes of anaemia. It may be due to loss of blood (haemorrhagic anaemia), resulting from an accident, operation, etc., or from chronic bleeding, as from an ulcer or haemorrhoids. Iron-deficiency anaemia results from lack of iron, which is necessary for the production of haemoglobin (see sideropenia). Haemolytic anaemias result from the increased destruction of red blood cells (which contain the pigment). This can be caused by toxic chemicals; *autoimmunity; the action of parasites, especially in *malaria; or conditions such as *thalassaemia and *sickle-cell disease, associated with abnormal forms of haemoglobin, or *spherocytosis, which is associated with abnormal red blood cells. (See also haemolytic disease of the newborn.) Anaemia can also be caused by the impaired production of red blood cells, as in *leukaemia (when red-cell production in the bone marrow is suppressed) or *pernicious anaemia. Aplastic anaemia is characterized by a failure of blood cell production resulting in *pancytopenia and reduced bone marrow cellularity.

Anaemias can be classified on the basis of the size of the red cells, which may be large (macrocytic anaemias), small (microcytic anaemias), or normal-sized (normocytic anaemias). (See also macrocytosis; microcytosis.) The treatment of anaemia depends on the cause. —anaemic adj.... anaemia

n. a bilobed organ in the root of the neck, above and in front of the heart. The thymus is enclosed in a capsule and divided internally by cross walls into many lobules, each full of T lymphocytes (white blood cells associated with antibody production). In relation to body size the thymus is largest at birth. It doubles in size by puberty, after which it gradually shrinks, its functional tissue being replaced by fatty tissue. In infancy the thymus controls the development of *lymphoid tissue and the immune response to microbes and foreign proteins (accounting for allergic response, autoimmunity, and the rejection of organ transplants). T lymphocytes migrate from the bone marrow to the thymus, where they mature and differentiate until activated by antigen. —thymic adj.... thymus