B cells are responsible for producing antibodies, an essential component of the specific immune system. Abnormal B cells lead to a deficiency in immunoglobulins (antibodies). Deficiency in immunoglobulins is called hypogammaglobulinemia. Clinically, this leads to a susceptibility to recurrent infections, particularly lower respiratory tract infections.
Selective Immunoglobulin A Deficiency
This is the most common immunoglobulin deficiency. Patients have low levels of IgA and normal levels of IgG and IgM.
IgA is present in secretions of the mucous membranes, such as saliva, respiratory tract secretions, GI tract secretions, tears and sweat. IgA protects against opportunistic infections of these mucous membranes.
Selective IgA deficiency is a mild immunodeficiency. Patients are often asymptomatic and never diagnosed. Patients have a tendency to recurrent mucous membrane infections, such as lower respiratory tract infections, and autoimmune conditions.
TOM TIP: The place you are likely to come across IgA deficiency is when testing for coeliac disease. The blood tests for coeliac disease are the IgA levels of anti-TTG and anti-EMA antibodies. When you test for these antibodies, it is important to also test for total immunoglobulin A levels. If the total IgA is low due to an IgA deficiency, the coeliac test will be negative, even when they have coeliac disease. In this circumstance, you can test for the IgG version of anti-TTG or anti-EMA antibodies or simply do an endoscopy with biopsies.
Common Variable Immunodeficiency
Common variable immunodeficiency is caused by a genetic mutation in the genes coding for components of B cells. The result is deficiency in IgG and IgA, with or without a deficiency in IgM. This leads to recurrent respiratory tract infections, typically leading to chronic lung disease over time. Patients are unable to develop immunity to infections or vaccinations. They are also prone to immune disorders such as rheumatoid arthritis, and cancers such as non-Hodgkins lymphoma. Management is with regular immunoglobulin infusions and treating infections and complications as they occur.
X-linked agammaglobulinaemia is also known as Bruton’s agammaglobulinaemia. This is an X-linked recessive condition. It results in abnormal B cell development and deficiency in all classes of immunoglobulins. It causes similar issues to common variable immunodeficiency.
Last updated January 2020