The five sub-classes of antibodies are:
Immunoglobulin A (IgA), which is found in high concentrations in the mucous membranes, particularly those lining the respiratory passages and gastrointestinal tract, as well as in saliva and tears.
– Protects against infections of the mucous membranes lining the mouth, airways, digestive tract
Immunoglobulin G (IgG), the most abundant type of antibody, is found in all body fluids and protects against bacterial and viral infections. (chronic inflammation)
– Major type of antibody found in the blood that can enter tissues; fights infection.
Immunoglobulin M (IgM), which is found mainly in the blood and lymph fluid, is the first antibody to be made by the body to fight a new infection. (acute inflammation)
– Large sized: Remains in the bloodstream where it can kill bacteria.
Immunoglobulin E (IgE), which is associated mainly with allergic reactions (when the immune system overreacts to environmental antigens such as pollen or pet dander). It is found in the lungs, skin, and mucous membranes.
– Frequently increased in parasitic infestations and atopic individuals (with allergic hypersensitivity)
Immunoglobulin D (IgD), which exists in small amounts in the blood, is the least understood antibody.
– Remains in the bloodstream to fight bacteria
IgA, IgG, and IgM are often measured together. That way, they can give doctors important information about immune system functioning, especially relating to infection or autoimmune disease.
What is Ig Testing?
An immunoglobulin test measures the level of certain immunoglobulins, or antibodies, in the blood. Antibodies are proteins made by the immune system to fight antigens, such as bacteria, viruses, and toxins.
The body makes different immunoglobulins to combat different antigens. For example, the antibody for chickenpox isn’t the same as the antibody for mononucleosis. Sometimes, the body may even mistakenly make antibodies against itself, treating healthy organs and tissues like foreign invaders. This is called an autoimmune disease.
Why It’s Done?
Once an antibody is produced against a specific antigen, the next time that antigen enters the body, the immune system “remembers” its response and produces more of the same antibodies. In that way, checking for the presence of specific immunoglobulins in the blood can be helpful in diagnosing or ruling out infections or certain other illnesses.
Doctors also rely on the immunoglobulin test as one of the tools to help diagnose immunodeficiencies (when the immune system isn’t working properly). A person can be born with an immunodeficiency or acquire it through infection, disease, malnutrition, burns, or as a side effect of medicines. Doctors may suspect an immunodeficiency in a child who experiences frequent or unusual infections.
Immunoglobulin levels are also used as part of an evaluation for autoimmune conditions such as juvenile idiopathic arthritis, lupus, and celiac disease.
Indications for the test:
1. Recurrent infections
2. Suspected myeloma, Waldenstrom’s macroglobulinaemia, lymphoma, connective tissue disease
IgA: raised in elderly, chronic infection, cirrhotic liver disease.
IgM: raised primary biliary cirrhosis, acute infection, EBV, CMV, TB.
IgG: marked polyclonal elevation is seen in HIV and Sjögren’s syndrome
- less marked elevation in chronic inflammatory and infective conditions including TB, occult abscess and protozoal infection.
Factors affecting the test
Age, primary / secondary immunodeficiency
Difference Between IgM and IgG
IgM is the first antibody to be produced in response to any antigen (foreign particle) invasion, while IgG is most abundantly found antibody in the human body. IgM is the largest immunoglobulin among all, with pentamer units and ten antigens binding site. IgG are responsible for humoral immunity and is a monomer unit which is lighter and smaller, with two antigen binding site. Due to the smaller size of this antibody, it is able to travel through the bloodstream.
|
BASIS FOR COMPARISON |
IMMUNOGLOBULIN Ig IgM |
IMMUNOGLOBULIN Ig IgG |
| Role | IgM serves as the first kind of defence, which means it is the first antibody to be immediately developed when any foreign particle is introduced, though its function is temporary. | IgG is a long-term response for any disease and thus protect our body from viral and bacterial attacks. |
| Where it is found | IgM is found in lymph fluid and blood and is produced in plasma cells. | Abundantly found in lymph, blood, and intestine. |
| Effect of high level | High level of IgM may give rise to parasitic infections, kidney damage, rheumatoid arthritis, hepatitis, mononucleosis. | High level of IgG in the body means a long-term infection like HIV, multiple sclerosis, multiple myeloma. |
| Effect of Low-level | Low level of IgM results in few types of leukaemia, and some inherited diseases. | Low level of IgG results in kidney damage and few types of infections. |
Due to the larger size, IgM is unable to cross the placenta, though it’s the first antibody produced in the human foetus while IgG is smaller in size and can cross the placenta and provides mother’s immunity to developing the embryo.
Infection: Current or Past?
IgM antibodies against HSV usually begin to form within 1-2 weeks after onset of the infection. The IgM antibody response usually declines rapidly such that after a few weeks or months (depending on the infection) they are undetectable. In contrast, IgG antibodies form more slowly, but persist for months or years.
– The presence of IgM class antibodies suggests recent infection.
– The presence of IgG antibodies only is indicative of past exposure.
Both IgG and IgM may be present at or soon after onset of illness and reach peak titers within 30 days.
The presence of IgG antibodies to an organism when accompanied by a negative IgM test for the same organism means that the person was exposed to that organism at one time and developed antibodies to it, but does not have a current active infection of that organism.
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