Types of Immunoglobulins their production and function

Immunoglobulins: These are antibodies present in blood which are produced by B cells and are used by immune system to identify and neutralize foreign objects such as bacteria, virus and any foreign objects. These immunoglobulins recognize the antigen part of the foreign body entering into the human body which can be bacteria, virus, fungus, spores, cancer cells …etc

Here we are going to discuss some important aspects about each type of immunoglobulin.

Immunoglobulin G:

• Immunoglobulin G is named so because of he presence of Gamma H chain
• It is also called as WARM immunoglobulin
• IgG has a half life of 23 days
• IgG comprises 80% of immunoglobulins
• It is a major serum immunoglobulin
• IgG is divided into 4 sub classes: IgG1, IgG2, IgG3, IgG4 which are divided in human serum inthe concentration of 65%, 23%, 8%, 4%
• IgG is the smallest immunoglobulin
• It is present in serum at a concentration of 8-16 mg per ml
• IgG is the only maternal immunoglobulin that crosses placenta and responsible for providing natural passive immunity in newborn
• Classical compliment fixation is positive
• Predominant Immunoglobulin present in Gingival crevicular fluid – GCF
• It is secreted in Milk

Immunoglobulin M:

• It is also called as COLD immunoglobulin
• It is named so because of the presence of Mu H chain
• IgM has a half life of 5 days
• IgM comprises 5-8 % of immunoglobulins
• It is the earliest immunoglobulin synthesized by foetus to counter infections
• It is the oldest immnunoglobulin class
• IgM antibodies are short lived with a half life of 5 days, hence presence of IgM in serum indicates recent infection
• IgM also activates classical pathway of compliment fixation
• The presence of IgM in foetus or new born it indicates intrauterine infection and will be helpful in diagnosis of congenital infections such as Syphilis, rubella, hiv infection ..etc
• Both IgG and IgM are involved in Type II or cytotoxic type of hypersensitivity reaction

Immunoglobulin A:

• It is named so because of the presence of Alpha H chain
• IgA has a half life of 6 days
• IgA occurs in 2 forms i.e Serum IgA and Secretory IgA
• It is the second most abundant class of immunoglobulin having 10-13% of the total immumoglobulin
• It is the predominant immunoglobulin in saliva
• It is the immunoglobulin present in exocrine secretions called as secretory IgA which is produced by mucosal and glandular epithelium which protects igA serum from proteolysis
• IgA occurs in 2 forms 1. Serum IgA 2. Secretory IgA
• It activates alternate pathway of compliment fixation
• It is secreted in Milk

Immunoglobulin E:

• It is named so because of the presence of Epsilon H chain
• IgE has a half life of 2-8 days
• IgE percentage of all Immunoglobulins is 1%
• It has a unique property of heat liability i.e IgE is inactivated at 56 degrees centigrade in 1 hour
• It has affinity for mast cells of same species (Homocytotropism)
• Mediates Prausunitz-Kustner reaction, a method to detect atopic antibody
• It is responsible for anaphylactic type of hypersensitivity reactions: Eg Contact Dermatiis
• It is chiefly produced in the lignings of respiratory and intestinal tracts
• It is believed to have a special role in parasitic reactions
• Elevation of IgE levels are seen in allergic conditions like hay fever, eczema and asthma.

Immunoglobulin D:

• It is named so because of the presence of Delta H chain
• It structurally resembles IgG
• IgD and IgM serves as recognition receptors of antigens
• It activates the B- lymphocytes for antibody production or suppression