Immunoglobulin types and their functions

What is Immunoglobulin

Antibodies are specific glycoprotein configurations produced by B-lymphocytes and plasma cells in response to a specific antigen and capable of reacting with that antigen.

In simple words, Immunoglobulins are glycoprotein molecules that are produced by plasma cells in response to an immunogen and which function as antibodies

• Antibodies also called Immunoglobulins constitute the gamma globulin portion of blood proteins.
• Are soluble proteins secreted by activated B cells and plasma cells in response to an antigen.
• Are capable of binding specifically with that antigen.

 

Functions of antibodies

• To recognize and bind with antigen
• To remove or kill or neutralize in collaboration with other components of immune system.

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Bullet points on Immunoglobulins - Important for exams

 

• Basic shape/structure of antibodies : Y-shaped

• Which antibody crosses placenta : IgG

• Immunoglobulin present in breast milk : IgA

• Immunuglobulin present in serum in maximum amount : IgG

• Which has pentameric structure : IgM

• Largest in size : IgM

• Largest in number : IgG

• Millionaire molecule : IgM (as its molecular weight is 90,000 to 1,00,000

• Most abundant immunoglobulin : IgG (approx 80%)

• Principal immunoglobulin in human serum : IgG

• Antibodies are produced by : Plasma cells

• Synthesis of antibodies takes place by : B- cells

• Plasma cell is a cell derived from B-lymphocyte.

• Produced in acute infection : IgM

• Indicates previous infection : IgG

• Immunoglobulin produced in Allergic response : IgE

• IgA is produced by : Mucous membranes of the body

• Antibodies present in colostrum : IgA

• Principal immunoglobulin isotype in secretions : IgA

• Function of IgD : Activation of B-cells (exact function of IgD is not known)

• Class of an immunoglobulin is determined by : determined by the heavy chain type

• Name the heavy chain of immunoglobulin IgM : μ (pronounce it as "myu")

• Name the heavy chain of immunoglobulin IgE : ε (pronounce it as "epsilon")

• First antibody to produce during the primary response to antigen : IgM

• First antibody which is made by the developing B-cells : IgM

• Immunoglobulins present in external secretion : IgA

• Immunoglobulin which takes part in hypersensitivity reaction : IgE

• Most abundant immunoglobulin in newborns : IgG

• Order of percent of total immunoglobulin in serum is :  IgG, IgA, IgM, IgD, IgE (learn it as "GAMD E")

• There is about 4 times as much IgG as IgA, 10 to 15 times as much as IgM, 300 times as much as IgD, and 30,000 times as much as IgE.

• IgG: 75%

• IgA: 10-15%

• IgM: 5-10%

• IgD: 0.2%

• IgE: 0.002%

• The antibody isotype IgE is made against parasitic worms (helminths) and arthropods.

• IgE sticks phagocytic eosinophils to helminths and arthropods for the extracellular killing of that organism.

• Antibody directly take part in opsonization process : IgG

• Reactions, such as coughing, sneezing, and vomiting can be induced by which immunoglobulin : IgE

• The complement is activated by : Both IgM and IgG

 

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MCQ's on Immunoglobulins : Take the test 

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Immunoglobulin types

There are five classes of Immunoglobulins (Ig):

1. IgG
2. IgM
3. IgA
4. IgD
5. IgE

(Many students learn it as GAMED, but I prefer to learn it as "GAMD E" - refer to bullet points for the reason)

 

Why they are named so?

Human Immunoglobulin Classes

• IgG - Gamma (γ) heavy chains
• IgM - Mu (µ) heavy chains
• IgA - Alpha (α) heavy chains
• IgD - Delta (δ) heavy chains
• IgE - Epsilon (ε) heavy chains

 

Human Immunoglobulin Light Chain Types

• Kappa (κ)
• Lambda (λ)

 

Human Immunoglobulin Subclasses

1). IgG Subclasses:

• IgG1 - Gamma 1 (γ1) heavy chains
• IgG2 - Gamma 2 (γ2) heavy chains
• IgG3 - Gamma 3 (γ3) heavy chains
• IgG4 - Gamma 4 (γ4) heavy chains

2). IgA subclasses:

• IgA1 - Alpha 1 (α1) heavy chains
• IgA2 - Alpha 2 (α2) heavy chains

 

Important Discoveries related to Immunoglobulins

• Porter proposed of a Y-shaped structure in 1962, after discovering Fc & Fab fragment in 1959.
• Edelman discovered 4 chains of Immunoglobulin.
• Porter & Edelman Won noble prize in 1972.

 

Immunoglobulin structure

• IgM is pentameric and monomeric
• IgA is monomeric, dimeric and secretory
• IgG, IgD, IgE are monomeric

 

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Properties of Immunoglobulin

 

IgG

• Structure: Monomer
• Percentage serum antibodies: 80%
• Major serum Ig (systemic immunity)
• Major Ig in extravascular spaces
• Because of its size it can escape from blood vessels more easily. - So it participates in the defence of tissue spaces and body surfaces
• Location: Blood, lymph, intestine
• Half-life in serum: 23 days
• Complement Fixation: Yes
• Placental Transfer: Yes
• Known Functions: Enhances phagocytosis, neutralizes toxins and viruses, protects foetus and new born, Compliment activation

 

IgM

• Structure: Pentamer and monomer
• Percentage serum antibodies: 5-10%
• 3rd highest serum Ig
• First Ig made by foetus
• and B cells
• Location: Blood, lymph, B cell surface (monomer)
• Half-life in serum: 5 days
• Complement Fixation: Yes
• Placental Transfer: No
• Known Functions: First antibodies produced during an infection. Effective against microbes and agglutinating antigens.

IgA

• Structure: Monomer, Dimer and Secretory
• Percentage serum antibodies: 10-15%
• 2nd highest serum Ig
• Major secretory Ig (Mucosal or Local Immunity)
• Tears, saliva, gastric and pulmonary secretions
• Location: Secretions (tears, saliva, intestine, milk), blood and lymph.
• 40 mg of secretory IgA /kg body weight is secreted through intestine (Total daily production of IgG 30 mg/kg)
• Half-life in serum: 6 days
• Complement Fixation: No
• Placental Transfer: No Known
• Functions: Localized protection of mucosal surfaces. Provides immunity to infant digestive tract.

 

IgD

• Structure: Monomer
• Percentage serum antibodies: 0.2%
• 4th highest serum Ig
• B cell surface Ig
• Location: B-cell surface, blood, and lymph cell surface
• Half-life in serum: 3 days
• Complement Fixation: No
• Placental Transfer: No Known
• Functions: In serum function is unknown. On B cell surface, initiate immune response.

 

IgE

• Structure: Monomer
• Percentage serum antibodies: 0.002%
• Location: Bound to mast cells and basophils throughout body in blood
• Least common serum Ig
• Binds to basophils and mast cells (Does not require Ag binding)
• Half-life in serum: 2 days
• Complement Fixation: No
• Placental Transfer: No
• Known Functions: Allergic reactions. Possibly lysis of worms.
• IgE mediates (type I) hypersensitivity reactions.

 

 

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1. IgE increases in:

• Atopic skin diseases such as eczema
• Hay fever
• Asthma
• Anaphylactic shock
• IgE-myeloma myeloma

 

2. IgE decreases in:

• Congenital agammaglobulinemia
• Hypogammaglobulinemia due to faulty metabolism or synthesis of immunoglobulins

 

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Important Points to know

• Antibodies themselves do not destroy antigen; they inactivate and tag it for destruction.
• All antibodies form an antigen-antibody (immune) complex
• Defensive mechanisms used by antibodies are neutralization, agglutination, precipitation and complement fixation.

 

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MCQ's on Immunoglobulins : Take the test 

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More useful resources on immunoglobulins

• Immunoglobulins : Important points for exam - Video lecture

• Structure of Immunoglobulins - Video lecture

• Wikipedia - Antibodies

• Immunoglobulin E -  Wikipedia

• Immunoglobulin Test - WebMD

• Classes of Immunoglobulins

• The distribution and functions of immunoglobulin isotypes

 

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