Immunoglobulins (Gamma Globulins)-
The term immunoglobulin was introduced in 1959 for serum proteins formerly known as gamma globulins. Immunoglobulins are very important in the study of immunity and are formed by the reticuloendothelial system in the body.
Immunoglobulins-A protein produced by plasma cells and lymphocytes and characteristic of these types of cells. Immunoglobulin’s play an essential role in the body's immune system. They attach to foreign substances, such as bacteria, and assist in destroying them.
The human immunoglobulin system (human serum) consists of five classes which are distinguished from each other on the basis of antigenicity and on the basis of physical and chemical properties. Namely-
Found in Mucosal areas, such as the gut respiratory trac and urogenital tract, and prevents colonization by pathogens. Also found in saliva, tears, and breast milk.
Functions mainly as an antigen receptor on B cells that have not been exposed to antigens. It has been shown to activate basophils and mast cells to produce Antimicrobial factors.
Binds to allergens and triggers histamine release from mast cell and basophils, and is involved in allergy. Also protects against parasitic worms.
In its four forms, provides the majority of antibody-based immunity against invading pathogens. The only antibody capable of crossing the placenta to give passive immunity to the fetus.
Expressed on the surface of B cells and in a secreted form with very high avidity. Eliminates pathogens in the early stages of B cell-mediated immunity before there is sufficient IgG.
IgG is the most abundant immunoglobulin of serum and it comprises 80% of the serum antibodies of the normal human being. It contains four subclasses IgG1, IgG2, IgG3 and IgG4 and all the four subclasses diffuse in the interstitial fluid. IgG is the only class of immunoglobulin which is transported across the placenta and is responsible for all the immunity which the foetus acquires by the placental route. The normal human infant is born with IgG equal to or higher than that of the mother.
It constitutes 10% of the antibodies in the human serum. It contains two subclasses IgA1, and IgA2. It is present in many body fluids such as milk, saliva, tears, mucous secretions of respiratory, genitourinary and intestinal tracts and prevents the passage of organisms into circulation through minute leakage in the mucous surfaces of these tracts. IgA synthesis begins about 2 weeks after birth and in one year reaches a level of 4 to 5% of the adult.
It constitutes 5 to 10% of the antibodies in the human serum. It is a large antibody molecule often called macroglobulin. Because of its large molecular weight, IgM antibodies remain largely intravascular and cannot pass through placenta. IgM antibody molecules are capable of killing bacteria more effectively and thus cause lysis of cells. IgM antibodies are short lived.
It comprises less than 1% of the total immunoglobulin. It has not been shown to have antibody activity although it is found in greater amounts in some sera obtained from individuals with chronic infections.
It comprises the smallest fraction of immunoglobulin in the body. Normally, it is found in traces in serum. It has a distinctive biological activity which identifies it easily. It is concentrated in submucous tissues and is the major antibody responsible for symptoms of immediate allergy and anaphylaxis.