IgG subclass deficiency
What is IgG?
IgG or immunoglobulin G is the most prevalent form of antibody. Antibodies are small proteins produced by plasma cells. They are essential part of the humoral or circulating immune system.
IgG is composed of 4 peptide chains: 2 heavy chains and 2 light chains. There are 4 subclasses of IgG.
What is IgG subclass deficiency?
Patients with IgG deficiency have a normal total level of IgG but low levels of at least one of the IgG subclasses. Each of these subclasses has a slightly different immune function:
- IgG-1 forms antibodies against protein antigens like tetanus
- IgG-2 forms antibodies against antigens like pneumonoccal polysaccharides
- IgG-3 forms antibodies to antigens similar to IgG-1
- IgG-4 forms antibodies to extracellular parasites
In patients with IgG subclass deficiency, other components of the immune system function normally.
What causes IgG subclass deficiency?
Thepattern of inheritance connected with this disorder is not known. IgG subclass deficiency can affect both males and females. However, partial gene deletions have been discovered in some patients with selective IgA deficiency.
What are the signs and symptoms of IgG subclass deficiency?
Patients with IgG subclass deficiency may present with:
- Frequent or chronic infections, especially from Streptococcus, Haemophilus and Branhamella catarrhalis species
- Common infections such as otitis media, sinusitis, pneumonia, and bronchitis
- Recurrent bouts of sepsis and meningitis
- Asthma and atopic dermatitis
How is IgG subclass deficiency diagnosed?
Diagnosis of IgG subclass deficiency is largely made on patient medical history and physical exam. IgG subclasses can be measured but the results of this testing are not always conclusive. Levels should be tested again in several months to determine if the values are truly abnormal.
Diagnosis should also take into account the patient’s overall health, presenting symptoms, and response to vaccines.
How is IgG subclass deficiency treated?
IgG subclass deficiency is treated with:
- Antibiotics for infection control
- Pneumonoccal vaccine to strengthen immune response against pneumococcal infection
- IgG therapy, if more conservative measures are not successful
What is specific antibody deficiency?
A patient with a specific antibody deficiency lacks the ability to produce IgG molecules, which play a vital role in the body’s immune defense system. Specific antibody deficiency is also called partial antibody deficiency or impaired polysaccharide responsiveness.
What causes specific antibody deficiency?
The exact cause of specific antibody deficiency is not known. It is speculated that it is due to a breakdown in communication between B cells and other cells in the immune system.
What are the signs and symptoms of specific antibody deficiency?
Some patients with specific antibody deficiency are asymptomatic because other components of their immune system are still functional. Other patients may present with:
- Otitis media, sinusitis, bronchitis and pneumonia
- Infections that are not as severe as those with severe combined immunodeficiency or x-related agammaglobulinaemia
How is specific antibody deficiency diagnosed?
The diagnosis of specific antibody deficiency is based on:
- History of recurrent respiratory infections
- Testing levels of IgG subclasses
- Administering the pneumonococcal vaccine then testing for antibody formation after 4–6 weeks
How is specific antibody deficiency treated?
Treatment for specific antibody deficiency centres on:
- Infection control with antibiotics at high dosage for 10 days or daily as prophylaxis against infection
- Immunoglobulin replacement therapy administered intravenously or subcutaneously, if indicated
Main goals of treatment are to prevent bronchiectasis and scarring in the lungs from repeated respiratory infections and to maintain overall quality of life.
What is the prognosis for specific antibody deficiency?
The prognosis for patients with specific antibody deficiency is generally good. Children have been known to outgrow specific antibody deficiency naturally and those who do not are still able to maintain good quality of life with antibiotic and/or immunoglobulin therapy.