Antibody Deficiencies

Agammaglobulinemia: X-Linked and Autosomal Recessive
The basic defect in both X-Linked Agammaglobulinemia and autosomal recessive agammaglobulinemia is a failure of B-lymphocyte precursors to mature into B-lymphocytes and ultimately plasma cells. Since they lack the cells that are responsible for producing immunoglobulins, these patients have severe deficiencies of all types of immunoglobulins.

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Common Variable Immune Deficiency
Common Variable Immune Deficiency (CVID) is a frequently diagnosed immunodeficiency, especially in adults, characterized by low levels of serum immunoglobulins and antibodies, which causes an increased susceptibility to infection.

While CVID is thought to be due to genetic defects, the exact cause of the disorder is unknown in the large majority of cases.
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Selective IgA Deficiency
Individuals with Selective IgA Deficiency lack IgA, but usually have normal amounts of the other types of immunoglobulins. Selective IgA Deficiency is relatively common in Caucasians. Many affected people have no illness as a result. Others may develop a variety of significant clinical problems.

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IgG Subclass Deficiency
The main immunoglobulin (Ig) in human blood is IgG. This is the second most abundant circulating protein and contains long-term protective antibodies against many infectious agents. IgG is a combination of four slightly different types of IgG called IgG subclasses: IgG1, IgG2, IgG3 and IgG4.

When one or more of these subclasses is persistently low and total IgG is normal, a subclass deficiency is present. Although this deficiency may occasionally explain a patient’s problems with infections, IgG subclass deficiency is a controversial diagnosis and experts disagree about the importance of this finding as a cause of repeated infections.

The misdiagnosis of IgG subclass deficiency as a cause of presumed immunodeficiency is common, often leading to the unnecessary long-term use of Ig replacement therapy. A subclass deficiency needs to be considered and looked for only under special circumstances.

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Specific Antibody Deficiency
Among the five classes of immunoglobulins: IgG, IgA, IgM, IgD, and IgE, IgG has the predominant role in protection against infection. Some patients have normal levels of immunoglobulins and all forms of IgG, but do not produce sufficient specific IgG antibodies that protect us from some viruses and bacteria.

Patients who otherwise produce normal immunoglobulin levels but who lack the ability to produce protective IgG molecules against the types of organisms that cause upper and lower respiratory infections are said to have Specific Antibody Deficiency (SAD).
SAD is sometimes termed partial antibody deficiency or impaired polysaccharide responsiveness.

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Transient Hypogammaglobulinemia of Infancy
An unborn baby makes no IgG (antibody) and only slowly starts producing it after birth. However, starting at about the sixth month of pregnancy, the fetus starts to receive maternal IgG antibody through the placenta. This increases during the last trimester of pregnancy until at term birth the baby has a level of IgG, the main class of antibody in the circulation, equivalent to that of the mother.

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Other Antibody Deficiency Disorders
In addition to the more common immunodeficiencies described in other chapters, there are several other rare, but nevertheless well-described, antibody deficiency disorders. Similar to the patients described in the chapters on X-Linked Agammaglobulinemia (XLA), Hyper IgM Syndrome, Selective IgA Deficiency, Common Variable Immune Deficiency (CVID) and Specific Antibody Deficiency (SAD), individuals with less common antibody deficiencies usually present with upper respiratory infections or infections of the sinuses or lungs, typically with organisms like streptococcus pneumonia and hemophilus influenzae.

Laboratory studies show low immunoglobulins and/or deficient specific antibody production. Many of these disorders also include abnormalities in the cells responsible for generating or maintaining an antibody response. The patients often improve with antibiotics but get sick again when these are discontinued. The cornerstone of therapy for antibody deficiency disorders is immunoglobulin (Ig) replacement.

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