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glossary:globulin

Globulin

A family of proteins found in abundance in plasma. They include the gamma globulins, which in turn include the various antibody molecules produced by the immune system.

A specialized class of serum proteins, which may occur naturally in serum, but are usually produced following exposure to an almost limitless (>107) number of antigens. Called also antibody. Immunoglobulins combine only with the antigen (or one closely related to it) that elicited their production. Immunoglobulins are major components of what is called the humoral immune response system. They are synthesized by B lymphocytes and their derivative plasma cells, and are found in the serum and in other body fluids and tissues, including the urine, spinal fluid, lymph nodes and spleen.

Immunoglobulin molecules consist of two kinds of polypeptide chains: heavy chains (H-chains) and light chains (L-chains). There are five antigenically different kinds of H-chains, designated ?, µ, a, d and e, and this difference is the basis for the classification of immunoglobulins. Classes vary in their chemical structure and in the number of antigen-binding sites.

The five classes of immunoglobulins (Ig) are: IgG, IgM, IgA, IgD and IgE. Only IgG, IgM and IgA are found in all species of domestic animals.

IgA is present in low concentrations in the serum, but it is the major immunoglobulin of secretions and has a major first-line defense role in infections that enter via mucosal surfaces. Two IgA molecules are linked by a polypeptide called the secretory piece and by a J chain. Secretory IgA is present in nonvascular fluids, such as saliva, bile, synovial fluid, and intestinal and respiratory tract secretions. Both secreted and circulating IgA types are known to have antiviral properties; their production is preferentially stimulated by local administration of antigens such as oral and aerosol immunizations.

IgD is found in trace quantities in the serum in humans and chickens. It is found on the surface of B lymphocytes. Its function is uncertain.

IgE, once called reaginic antibody, is present in very low levels in serum and is generally present in increased levels in individuals with allergy. It has not been found in the chicken. IgE binds to Fc receptors on the surface of cells particularly mast cells and basophils, via the Fc part of the molecule. Following exposure to antigen (allergen), and its binding to the Fab of two adjacent IgE molecules, perturbations of the cell membrane are produced, leading to the release of vasoactive amines, particularly histamine and serotonin, which are the mediators of anaphylaxis and atopic reactions, including urticaria, asthma, hayfever and gastroenteritis. Allergic reactions such as urticaria, atopy and anaphylactic shock are examples of IgE-mediated reactions. It is recognized in humans and dogs that there is an inherited (familial) predisposition for certain individuals to produce IgE.

IgG is the most abundant of the five classes of immunoglobulins, representing about 80% of serum immunoglobulin protein. It is the major antibody in the secondary humoral response of immunity, serves to activate the complement system, and is frequently involved in opsonization. IgG is the only immunoglobulin that crosses the placenta and is the major component of passive maternal antibody transfer via colostrum and yolk.

IgM is the first antibody produced in the primary immune response. It represents about 20% of serum antibodies. Like the IgG, IgM bound to antigen activates the complement system, and together these two classes of immunoglobulins serve as specific antitoxins against the toxins of diphtheria, tetanus, botulism and anthrax microorganisms, and snake venoms, and play a major role in defense against most infectious diseases.

Structure of an immunoglobulin molecule. By permission from Tizard IR, Veterinary Immunology. An Introduction, Saunders, 2001

(2) globulin /glob·u·lin/ (glob´u-lin) any of a class of proteins insoluble in water, but soluble in saline solutions (euglobulins), or water-soluble proteins (pseudoglobulins); their other physical properties resemble true globulins.

(3) a general term for proteins that are insoluble in water or highly concentrated salt solutions but soluble in moderately concentrated salt solutions. All plasma proteins except albumin and prealbumin are globulins. The plasma globulins can be separated into five fractions by serum protein electrophoresis (SPE). In order of decreasing electrophoretic mobility these fractions are the alpha1, alpha2, beta1 and beta2 globulins, and the gamma globulins. The globulins include carrier proteins, which transport specific substances; acute phase reactants, which are involved in the inflammatory process; clotting factors; complement components; and immunoglobulins. Examples are transferrin, a beta1 globulin that transports iron, and alpha1-antitrypsin, an acute phase reactant that inhibits serum proteases. The gamma globulin fraction is almost entirely composed of immunoglobulins.

Types of Globulin

A-globulins

Serum globulins with the most rapid electrophoretic mobility, further subdivided into faster a1- and slower a2-globulins.

AC globulin

Accelerator globulin coagulation factor V.

Alpha globulins

A type of protein present in plasma. Alpha globulins perform diverse functions in the circulation, such as transporting various substances by combining reversibly with them, transporting other proteins from within the body, and acting as substrates for the formation of other substances.

Antihemophilic globulin

(AHG) any of a class of proteins insoluble in water, but soluble in saline solutions (euglobulins), or water-soluble proteins (pseudoglobulins); their other physical properties resemble true globulins.

Coagulation factor VIII. Factor VIII -A coagulation (clotting) factor. Classic haemophilia (haemophilia A) is due to a congenital deficiency in the amount (or activity) of factor VIII. Factor VIII is also known as antihemophiliac factor (AHF) or antihemophiliac globulin (AHG). The gene for factor VIII (that for classic haemophilia) is on the X chromosome so females can be silent carriers without symptoms and males can be haemophiliacs.

Antilymphocyte globulin

(ALG) the gamma globulin fraction of antilymphocyte serum (q.v.), used as an immunosuppressant in organ transplantation.

Antithymocyte globulin

(ATG) The gamma globulin fraction of antiserum derived from animals (e.g., rabbits) that have been immunized against human thymocytes; it causes specific destruction of T lymphocytes, used in treatment of allograft rejection. An immunosuppressive agent that selectively destroys T lymphocytes. Antithymocyte globulin is the gamma globulin fraction of antiserum from animals that have been immunized against human thymocytes. It is a polyclonal antibody.

The uses of this drug include the prevention and treatment of transplant rejection, aplastic anemia, and other conditions in which immunosuppression may be indicated. Pretreatment with this drug quashes rogue T cells in the DiGeorge syndrome and permits a successful thymus transplant.

Antithymocyte globulin is abbreviated ATG. The brand name is Thymoglobulin. It is produced in rabbits.

ß-globulins

Globulins in plasma which, in neutral or alkaline solutions, have an electrophoretic mobility between those of the alpha and gamma globulins.

B-globulins

Gamma globulins serum globulins having the least rapid electrophoretic mobility; the fraction is composed almost entirely of immunoglobulins.

Bacterial polysaccharide immune globulin

(BPIG) A human immune globulin derived from the blood plasma of adult human donors immunized with Haemophilus influenzae type b, pneumococcal, and meningococcal polysaccharide vaccines; used for the passive immunization of infants under 18 months of age.

Beta globulins

ß. A type of globulin in blood plasma that in electrically charged solutions exhibits colloidal mobility between that of the alpha and gamma globulins.

Colostral immunoglobulin

Colostrum contains a high level of IgG for several days after parturition. Following ingestion, colostral IgG molecules are absorbed unchanged across the intestinal mucosa for the first 1 to 2 days in cattle, dog, pig and horse and for up to 4 days in the sheep and goat. IgA is also present in colostrum but is not translocated to the circulation of the suckling animal to any extent; it may provide some local gut immunity

Cytomegalovirus immune globulin

A purified immunoglobulin derived from pooled adult human plasma selected for high titers of antibody against cytomegalovirus (CMV); used for the treatment and prophylaxis of cytomegalovirus disease in transplant recipients.

Hepatitis B immune globulin

A specific immune globulin derived from blood plasma of human donors with high titers of antibodies against hepatitis B surface antigen; used as a passive immunizing agent.

Hyperimmune globulin

Any of various immunoglobulin preparations especially high in antibodies against certain specific diseases.

Immune globulin

1. Immunoglobulin. A protein of animal origin with known antibody activity, synthesized by lymphocytes and plasma cells and found in serum and in other body fluids and tissues; abbreviated Ig. There are five distinct classes based on structural and antigenic properties: IgA, IgD, IgE, IgG, and IgM.

2. A concentrated preparation of gamma globulins, predominantly IgG, from a large pool of human donors; used for passive immunization against measles, hepatitis A, and varicella and for replacement therapy in patients with immunoglobulin deficiencies.

Immune human serum globulin

immune g. Immune globulin intravenous (human) a preparation of immune globulin suitable for intravenous administration; used in the treatment of primary and secondary immunodeficiency states, idiopathic thrombocytopenic purpura, and Kawasaki disease.

Immune serum globulin

Immune g. (2)

Pertussis immune globulin

A specific immune globulin derived from the blood plasma of human donors immunized with Pertussis vaccine; used for the prophylaxis and treatment of pertussis.

Rabies immune globulin

A specific immune globulin derived from blood plasma or serum of human donors who have been immunized with rabies vaccine and have high titers of rabies antibody; used as a passive immunizing agent.

Respiratory syncytial virus immune globulin

Intravenous a preparation of immunoglobulin G (IgG) from pooled adult human plasma selected for high titers of antibodies against respiratory syncytial virus; used for passive immunization of infants and young children.

Rh0(D) immune globulin

A specific immune globulin derived from human blood plasma containing antibody to the erythrocyte factor Rh0(D); used to prevent Rh-sensitization of Rh-negative females and thus prevent erythroblastosis fetalis in subsequent pregnancies; administered within 72 hours after exposure to Rh-positive blood resulting from delivery of an Rh-positive child, abortion or miscarriage of an Rh-positive fetus, or transfusion of Rh-positive blood; also used to stimulate the platelet count in idiopathic thrombocytopenic purpura.

Secretory immunoglobulin A

IgA Immunoglobulin in which two IgA molecules are linked by a polypeptide (secretory piece) and by a J chain; it is the predominant immunoglobulin.

Serum globulin

The fraction of proteins precipitated from blood serum by half saturation with ammonium sulfate; the principal groups include the a-, ß- and ?-globulins.

Serum globulins

All plasma proteins except albumin, which is not a globulin, and fibrinogen, which is not in the serum; they are subdivided into a-, ß-, and b-globulins.

Sex hormone–binding globulin

(SHBG) A ß in plasma that binds to and transports testosterone, and to a lesser degree estrogens.

Specific immune globulin

A preparation of immune globulin derived from a donor pool preselected for a high antibody titer against a specific antigen.

Tetanus immune globulin

A specific immune globulin derived from the blood plasma of human donors who have been immunized with tetanus toxoid; used in the prophylaxis and treatment of tetanus.

Vaccinia immune globulin

A blood product rich in antibodies against vaccinia, the virus in the smallpox vaccine. Vaccinia immune globulin (VIG) is the only known antidote to the complications of vaccination. It is derived from the blood of people who have been vaccinated recently, usually within the past 2 months. VIG is believed to be used against some but not all of the complications. namely extensive accidental implantation, eczema vaccinatum, severe or recurrent generalized vaccinia, and progressive vaccinia

Studies in the 1950's and 60's indicated that the complications of vaccination occurred soon after vaccination and before significant antibody could be detected in the blood. As a result, the late Dr. Henry Kempe and others developed the concept of providing antibody in the form of gamma globulin. Empiric evidence appeared to demonstrate that patients healed when VIG was administered for certain complications. Vaccination and the occurrence of complications ceased in the early 1970's and no definitive studies were carried out to determine the exact efficacy of VIG.

Varicella-zoster immune globulin

(VZIG) A specific immune globulin derived from plasma of human donors with high titers of varicella-zoster antibodies; used as a passive immunizing agent.

glossary/globulin.txt · Last modified: 2012/10/16 14:40 (external edit)