Immunoglobulin Deficiency Syndromes

Immunoglobulin * deficiency syndromes (IDS) are immunodeficiencies in which some or all antibodies * are deficient or absent, resulting in susceptibility to frequent, severe, or unusual infections.

What Are Immunoglobulin Deficiency Syndromes?

There are many types of IDS, most of which are inherited or primary immunodeficiencies. Secondary immunodeficiencies are caused by an underlying disease or outside agent, such as HIV * or chemotherapy * .

The immune system

B-cells or B lymphocytes are the antibody-producing cells of the humoral or antibody-mediated immune response. Bone marrow * stem cells develop into precursor B lymphocytes, which mature into B-cells. Each B-cell produces a specific antibody that recognizes and binds to a specific foreign antigen * , such as a bacterium or virus. When a B-cell encounters its antigen, it is stimulated to become a plasma cell and produces large amounts of antibodies that recognize that antigen.

Antibodies are protein molecules called immunoglobulins (Igs). There are five major classes of Igs:

  1. IgG is the most long-lasting and abundant antibody, present in large amounts in the bloodstream and tissues.
  2. IgM is the first type of antibody produced by B-cells. Later in the immune response, IgM is replaced by a different Ig class with the same antigenic specificity.
  3. IgA antibodies are secreted in tears, bile * , saliva, and mucus * . They protect the respiratory (breathing passages and lungs) system and gastrointestinal (organs of the digestive system) tracts from infection.
  4. IgE antibodies are responsible for allergic reactions.
  5. IgD antibodies may help regulate B-cell function. They are present in only minute amounts.

Igs consist of four chains of amino acids * : two longer heavy chains and two shorter light chains that together form a Y-shaped protein. Each arm of the Y forms a binding site for the antibody's specific antigen.

T cells or T lymphocytes are part of the cellular or cell-mediated immune response:

What Is Bruton's Agammaglobulinemia?

XLA was one of the first known immunodeficiency disorders. It was described in 1952 by Ogden Bruton (1908–2003).

In 1993, the gene that causes XLA was discovered on the X chromosome. It was named BTK for Bruton's tyrosine kinase.

Most IDS result from a failure in either the maturation of B-cells or the ability of B-cells to switch from one type of Ig production to another. With some types of IDS, the cellular immune system * retains its functions. However, B-cells are dependent on T-cells for producing antibodies; thus, some Ig deficiencies result from impaired T-cell function.

Primary IDS

Primary IDS are caused by genetic * defects that are inherited as either X-linked or autosomal recessive traits. Recessive traits are usually only apparent in the absence of a normal copy of a gene. Because males have only one X chromosome, inherited from their mothers, genes for recessive disorders that are located on the X chromosome (X-linked) usually cause disease only in males. Females have two X chromosomes and are unlikely to inherit two X-linked defective genes * , although they can pass a defective gene on to their offspring. Autosomal recessive IDS are caused by defective genes on chromosomes other than the X chromosome. Autosomal recessive IDS affect both males and females, but tend to be less common than X-linked IDS.

There are many different types of primary IDS, involving many different genes. Some cause deficiencies in all types of Ig molecules and some affect only one or a few types: