Also found in: Dictionary, Thesaurus, Medical.
Related to Immunoglobulins: immunoglobulin G



(Ig), globular proteins present in the blood serum of vertebrates and man.

Immunoglobulins form a group of chemically similar carbohydrate-containing compounds. All immunoglobulins appear to be antibodies to certain antigens. There are five classes of human immunoglobulins: G, M, A, D, and E (see Table 1). The immunoglobulins of the G class (IgG) have received the most study. Their molecules are constructed of two identical light (molecular weight, 22,000) and two identical heavy (molecular weight, 55,000–70,000) polypeptide chains connected by disulfide bonds (see Figure 1). When split by proteolytic enzymes (for example, papain), the immunoglobulin molecule breaks down into three parts: two identical fragments, designated Fab, that remain capable of being bound to an antigen, and a fragment designated Fc that helps the immunoglobulins to cross biological membranes. All three fragments are connected by short, flexible sections in the middle of the heavy chain. Flexibility permits the immunoglobulin molecules to combine optimally with antigens possessing different spatial structure. The parts of the molecules responsible for combining with antigens (the active center) are formed by the N-terminal segments (carrying the amino group NH2 at the end) of the heavy and light chains. The sequence of amino acids in these segments is specific to each IgG, and it scarcely varies in other parts of the chains. Immunoglobulins are classified according to the differences in structure of the heavy chains.

Figure 1. Diagram of a molecule of immunoglobulin G, showing two heavy and two light polypeptide chains connected by disulfide bonds. The light chain consists of two structural units (loops) formed by intrachain disulfide bonds; the heavy chain consists of four of these units. The thick lines denote the N-terminal segments of the chains. The arrow indicates the section sensitive to proteolysis, a process that results in the breakdown of the molecule into two Fab fragments, which retain antibody activity, and a third, Fc, fragment.

Most antibodies are of the IgG class (for example, the gamma globulins used for therapeutic purposes consist chiefly of IgG). The IgM are evolutionarily the oldest immunoglobulins and they are synthesized during the initial stages of the immune response. Their molecules are made up of five monomeric subunits, each

Table 1. Characteristics of the different classes of inmunoglobulins in a healthy person
ClassMolecular weightCarbohydrate content (in percent)Content in serum (in mg percent)
IgG .........140,0002800-1,680
IgM .........900,0001050-190
IgA .........170,000 and up7140-420
IgD .........180,000123-40
IgE .........196,000100.01-0.14

of which resembles the IgG molecule. The IgA are characteristically capable of penetrating various secretions (saliva, colostrum, intestinal juice), where they are found in polymeric form. The antibodies that participate in allergic reactions belong to the recently discovered IgE.

Immunoglobulins are synthesized by the lymphoid cells. After certain injuries to these cells, a large quantity of so-called myelomic immunoglobulins accumulates in blood and urine. Unlike the immunoglobulins of healthy persons, they are uniform in composition.


Haurowitz, F. lmmunokhimiia i biosintez anlitel. Moscow, 1969. (Translated from English.)
Nezlin, R. S. Biokhimiia antitel. Moscow, 1966.
Porter, R. “Struktura antitel.” In Molekuly i kletki, issue 4. Moscow, 1969. (Translated from English.)
Kabat, E. A. Structural Concepts in Immunology and Immunochemistry. New York, 1968.


References in periodicals archive ?
Immunoglobulins IgA, IgM, and IgG were measured using polyethylene glycol-enhanced immunoturbidimetric methods in which antihuman immunoglobulin in the reagent binds to immunoglobulin in the patient sample to generate a precipitate, thereby increasing the turbidity of the solution (3).
By binding to ghrelin, the immunoglobulins protect the hunger hormone from being broken down rapidly in the bloodstream.
Effect of a vigorous aerobic activity, immunoglobulins G and A on the immune system; Journal of Medicine, Guilan University of Medical Sciences.
ProteinPruTect also boosts immune function in light of stress from surgery—particularly when paired with immunoglobulin concentrate and arabinogalactan.
There are three major groups of immunoglobulins in the serum which are IgM, IgG (four subclasses), and IgA (two subclasses) and two minor groups which are IgD and IgE.
In the case of immunoglobulins, only IgG were found to be decreased significantly (P < 0.
We've been told that 60% of people get better after receiving a second lot of animal immunoglobulins, so we're keeping our fingers crossed.
However, IV immunoglobulin may be the next logical step to treat this severe condition.
Levels of both types of immunoglobulin had increased at 4 weeks, but decreased significantly at both 24 and 52 weeks; the results were most prominent for IgM, he said.
CVID is a primary immunodeficiency that affects the humoral arm of the immune system and interferes with the proper production of immunoglobulins.
Although the role of immunoglobulins in host defense against WNV infection is not completely understood, evidence suggests that humoral immunity protects against WNV infection and severe disease (7-9).

Full browser ?