Immunology Health Dictionary

(Singular: bacterium.) Simple, single-celled, primitive organisms which are widely distributed throughout the world in air, water, soil, plants and animals including humans. Many are bene?cial to the environment and other living organisms, but some cause harm to their hosts and can be lethal.

Bacteria are classi?ed according to their shape: BACILLUS (rod-like), coccus (spherical – see COCCI), SPIROCHAETE (corkscrew and spiral-shaped), VIBRIO (comma-shaped), and pleomorphic (variable shapes). Some are mobile, possessing slender hairs (?agellae) on the surfaces. As well as having characteristic shapes, the arrangement of the organisms is signi?cant: some occur in chains (streptococci) and some in pairs (see DIPLOCOCCUS), while a few have a ?lamentous grouping. The size of bacteria ranges from around 0.2 to 5 µm and the smallest (MYCOPLASMA) are roughly the same size as the largest viruses (poxviruses – see VIRUS). They are the smallest organisms capable of existing outside their hosts. The longest, rod-shaped bacilli are slightly smaller than the human erythrocyte blood cell (7 µm).

Bacterial cells are surrounded by an outer capsule within which lie the cell wall and plasma membrane; cytoplasm ?lls much of the interior and this contains genetic nucleoid structures containing DNA, mesosomes (invaginations of the cell wall) and ribosomes, containing RNA and proteins. (See illustration.)

Reproduction is usually asexual, each cell dividing into two, these two into four, and so on. In favourable conditions reproduction can be very rapid, with one bacterium multiplying to 250,000 within six hours. This means that bacteria can change their characteristics by evolution relatively quickly, and many bacteria, including Mycobacterium tuberculosis and Staphylococcus aureus, have developed resistance to successive generations of antibiotics produced by man. (METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS (MRSA)) is a serious hazard in some hospitals.

Bacteria may live as single organisms or congregate in colonies. In arduous conditions some bacteria can convert to an inert, cystic state, remaining in their resting form until the environment becomes more favourable. Bacteria have recently been discovered in an inert state in ice estimated to have been formed 250 million years ago.

Bacteria were ?rst discovered by Antonj van Leewenhoek in the 17th century, but it was not until the middle of the 19th century that Louis Pasteur, the famous French scientist, identi?ed bacteria as the cause of many diseases. Some act as harmful PATHOGENS as soon as they enter a host; others may have a neutral or benign e?ect on the host unless the host’s natural immune defence system is damaged (see IMMUNOLOGY) so that it becomes vulnerable to any previously well-behaved parasites. Various benign bacteria that permanently reside in the human body are called normal ?ora and are found at certain sites, especially the SKIN, OROPHARYNX, COLON and VAGINA. The body’s internal organs are usually sterile, as are the blood and cerebrospinal ?uid.

Bacteria are responsible for many human diseases ranging from the relatively minor – for example, a boil or infected ?nger – to the potentially lethal such as CHOLERA, PLAGUE or TUBERCULOSIS. Infectious bacteria enter the body through broken skin or by its ori?ces: by nose and mouth into the lungs or intestinal tract; by the URETHRA into the URINARY TRACT and KIDNEYS; by the vagina into the UTERUS and FALLOPIAN TUBES. Harmful bacteria then cause disease by producing poisonous endotoxins or exotoxins, and by provoking INFLAMMATION in the tissues – for example, abscess or cellulitis. Many, but not all, bacterial infections are communicable – namely, spread from host to host. For example, tuberculosis is spread by airborne droplets, produced by coughing.

Infections caused by bacteria are commonly treated with antibiotics, which were widely introduced in the 1950s. However, the con?ict between science and harmful bacteria remains unresolved, with the overuse and misuse of antibiotics in medicine, veterinary medicine and the animal food industry contributing to the evolution of bacteria that are resistant to antibiotics. (See also MICROBIOLOGY.)... bacteria

An immunological assessment used to monitor for signs of organ rejection after transplantation; it is also used to check the progress of treatment in patients with HIV (see AIDS/ HIV). The count measures the ratio of helper-induced T-lymphocytes to cytotoxic-suppressor lymphocytes. (See LYMPHOCYTE; IMMUNOLOGY.)... cd4/cd8 count

This is part of the body’s defence mechanism that comprises a series of 20 serum peptides (see PEPTIDE). These are sequentially activated to produce three signi?cant effects: ?rstly, the release of small peptides which provoke in?ammation and attract phagocytes (see PHAGOCYTE); secondly, the deposition of a substance (component C3b) on the membranes of invading bacteria or viruses, attracting phagocytes to destroy the microbes; thirdly, the activation of substances that damage cell membranes – called lytic components – which hasten the destruction of ‘foreign’ cells. (See IMMUNOLOGY.)... complement system

Gamma-globulin describes a group of proteins present in the blood PLASMA. They are characterised by their rate of movement in an electrical ?eld, and can be separated by the process of ELECTROPHORESIS. Most gamma-globulins are IMMUNOGLOBULINS. Gamma-globulin injection provides passive or active immunity against HEPATITIS A. (See also GLOBULIN; IMMUNITY; IMMUNOLOGY.)... gamma-globulin

A lower-than-normal amount of the protein GAMMA-GLOBULIN in the blood. The origin may be genetic – several types are inherited – or an acquired defect (for instance, some lymphomas cause the condition). Gamma-globulin largely comprises antibodies (IMMUNOGLOBULINS) so de?ciency of the protein reduces an individual’s natural resistance to infection (see IMMUNOLOGY).... hypogammaglobulinaemia

A specialist (medically or scienti?cally quali?ed) who practises or researches IMMUNOLOGY.... immunologist

An arti?cially prepared antibody (see ANTIBODIES) obtained from cell clones – a genetically identical group of cells – and comprising a single type of immunoglobulin. It neutralises only one speci?c ANTIGEN. The antibodies are prepared by linking antibody-forming lymphocytes (see LYMPHOCYTE) from the spleen of mice with myeloma cells from mice. Monoclonal antibodies are used in the development of new vaccines and in the study of human cells, hormones, and micro-organisms. Research is under way for their use in the treatment of some forms of cancer. (See IMMUNOLOGY.)... monoclonal antibodies

Burm. f.

Family: Myrsinaceae.

Habitat: Throughout India.

English: Embelia.

Ayurvedic: Vidanga, Krmighna, Krmihara, Krmiripu, Chitratandula, Jantughna, Jantunaashana, Vella, Amogha.

Unani: Baobarang, Barang Kaabuli.

Siddha/Tamil: Vaayuvidangam.

Action: Ascaricidal, anthelmintic, carminative, diuretic, astringent, anti-inflammatory, antibacterial, febrifuge. Used in diseases of chest and skin. Active principles are found to be oestrogenic and weakly progestogenic. Root—bechic, antidiarrhoeal. Seed—spermicidal, oxytocic, diuretic. The plant is also used for its blood purifying properties. It is an ingredient in cough syrups, preparations for anaemia, genitourinary tract infections, diarrhoea and diseases of the liver.

Embelin, isolated from the berries, shows significant anti-implantation and post-coital antifertility activity. (Successful trials have been carried out at the National Institute of Immunology, New Delhi on human beings.) It is found to be a potential male antifer- tility agent. Spermatogenesis has been impaired and sperm count reduced to the level of infertility. The antisper- matogenic changes are found to be reversible without any toxic effects.

Aqueous and EtOH extract of the fruit—anthelmintic against earthworms. Fruit powder (200 mg/kg), taken with curd on empty stomach, expelled tapeworm within 6-24 h. The treatment was also found effective in giardiasis. EtOH (50%) of the plant was found slightly active against E.coli. Di-salts of embelin—an- thelmintic. Amino salts exhibited less side effects than embelin. The effect of di-isobutyl amino derivatives lasted up to 10 h, also showed anti-inflammatory, hypotensive and antipyretic activities.

Berries gave quinones—embelin, ra- panone, homoembelin, homorapnone and vilangin.

Dosage: Fruit—5-10 g powder. (API Vol. I.)... embelia ribes

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

The ?uid which separates from blood, LYMPH, and other body ?uids when clotting occurs (see COAGULATION; HAEMORRHAGE). PLASMA is the ?uid of the blood, including FIBRIN, which carries the circulating blood cells and PLATELETS.

Serum is a clear, yellowish ?uid containing around 7 per cent proteins and globulins, small quantities of salts, fat, sugar, urea, and uric acid, and even smaller quantities of immunoglobulins, essential in the prevention of disease (see IMMUNITY; IMMUNOLOGY). The serum given in the commonly used vaccines is generally derived from horses’ blood, after they have been subjected to a long course of treatment.... serum

See IMMUNOLOGY.... serum therapy

Poisons produced by BACTERIA. (See also IMMUNITY; IMMUNOLOGY; MICROBIOLOGY.) Toxins are usually soluble, easily destroyed by heat, sometimes of the nature of crystalline substances, and sometimes ALBUMINS. When injected into animals in carefully graduated doses, they bring about the formation of substances called antitoxins which neutralise the action of the toxin. These antitoxins are generally produced in excessive amount, and the SERUM of the animal when withdrawn can be used for conferring antitoxic powers upon other animals or human beings to neutralise the disease in question. The best known of these antitoxins are those of DIPHTHERIA and TETANUS. Toxins are also found in many plants and in snake venom.

Some toxins are not set free by bacteria, but remain in the substance of the latter. They are known as endotoxins and are not capable of producing antitoxins.... toxins

n. (in immunology) the extent to which a sample of blood serum containing antibody can be diluted before losing its ability to cause agglutination of the relevant antigen. It is used as a measure of the amount of antibody in the serum.... titre