A patient with chronic diarrhea was found to lack IgA in his secretions, althoug

Question

A patient with chronic diarrhea was found to lack IgA in his secretions, although he had a normal level of serum IgA. What was this patient found to be unable to produce? A patient with chronic diarrhea was found to lack IgA in his secretions, although he had a normal level of serum IgA. What was this patient found to be unable to produce? A patient with chronic diarrhea was found to lack IgA in his secretions, although he had a normal level of serum IgA. What was this patient found to be unable to produce?

Explanation / Answer

There are five types (classes) of immunoglobulins or antibodies in the blood: IgG, IgA, IgM, IgD and IgE. IgG is present in the largest amount, followed by IgM and IgA. IgD is much lower, and IgE is present in only minute amounts. IgM and IgG mainly protect us from infections inside our body tissues, organs and blood. While IgA is present in the blood, most of the IgA in the body is in the secretions of the mucosal surfaces, including tears, saliva, colostrum, genital, respiratory and gastrointestinal secretions.

The IgA antibodies in the secretions play a major role in protecting us from infections in these areas. IgG and IgM are also found in secretions but not in nearly the same amount as IgA. IgA present in these secretions is also termed secretory IgA. If human mucosal surfaces were spread out flat, they would cover an area equal to one and a half tennis courts, so the importance of IgA in protecting mucosal surfaces cannot be overstated.

Secretory IgA has some differences compared to the IgA present in the blood. Secretory IgA is made of two IgA antibody molecules joined together by a protein called the J chain (“J” for “joining”). In order for this unit to be secreted, it must also be attached to another protein called the secretory piece. Therefore, the final secretory IgA unit that protects the mucosal surfaces is actually composed of two IgA molecules joined by the J chain and attached to the secretory piece.

Although individuals with Selective IgA Deficiency do not produce IgA (or produce only extremely small amounts), they do make all the other immunoglobulin classes; hence the term Selective IgA Deficiency. Furthermore, the functions of their T-lymphocytes, phagocytic cells and complement systems are all normal.

What is the defect in IgA deficiency ?

The primary defect in selective IgA deficiency is related to a failure of B cells to differentiate to mature isotype-switched surface IgA-positive B cells and IgA-secreting plasma cells with appropriate stimuli.

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