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Immunology Block 8
Common variable immunodeficiency
Atrophy, aplasia, and hypoplasia
Hyperimmunoglobulin E syndrome
Selective immunoglobulin A deficiency
Isolated primary immunoglobulin M deficiency
IgG subclass deficiency
Severe combined immunodeficiency
Hyper IgM syndrome
Adenosine deaminase deficiency
Leukocyte adhesion deficiency
Chronic granulomatous disease
Immunodeficiencies: Combined T-cell and B-cell disorders: Pathology review
Systemic lupus erythematosus
Selective immunoglobulin A deficiency
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Antonia Syrnioti, MD
Kara Lukasiewicz, PhD, MScBMC
Tanner Marshall, MS
Selective immunoglobulin A deficiency is a condition where there’s a lack of immunoglobulin or antibody A, called IgA for short. It’s called “selective” because all the other antibody classes, IgM, IgG, IgE and IgD are produced normally. IgA is in charge of protecting the mucosal surfaces of the body against foreign invaders, so without it, there’s a higher risk of mucosal infections.
Now, B cells make antibodies, and normally, B cells are “born” in the bone marrow, which is the spongy tissue inside some bones of the body. This is where they develop their B cell receptors on their surface which eventually can get released - and when they’re freely floating in the blood they’re called antibodies.
Antibodies are Y- shaped protein molecules, formed by two heavy and two light chains, each of which has a variable region, at one end, and a constant region (C region) at the other end. Variable regions are unique to each B cell and they are designed to bind to a very specific antigen, whereas C regions determine the antibody class.
Initially all of the B cells have IgM and IgD class antibodies on their surface, with each B cell recognizing and binding to its own unique antigen. Mature B cells leave the bone marrow and migrate to peripheral lymphoid organs, like the spleen, lymph nodes or mucosa-associated lymphoid tissue, which is also called MALT.
MALT is composed of clusters of lymphoid tissue scattered under the mucous membranes lining the mouth, airways, and digestive tract. This is a really strategic position, because a variety of antigens are constantly being picked up and filtered from these body tissues. As a result, B cells are likely to encounter an antigen they recognize. A bit like spending time at a train station during rush hour to look for someone that catches your eye.
Selective IgA deficiency is a common cause of immunodeficiency caused by low amounts of immunoglobulin A (IgA), resulting in low protection against infections of the mucous membranes lining the respiratory and gastrointestinal tracts. It is typically accompanied by normal levels of IgM, IgD, and IgG, and slightly elevated levels of IgE. Affected people are susceptible to infections of the mucous membranes lining the mouth, airways, and digestive tract.
Selective IgA deficiency often results from a failure of B cells to differentiate into IgA-secreting plasma cells, so IgA remains bound to their surface, along with IgM and IgD. Most people with selective IgA deficiency generally appear healthy, with no major symptoms. Sometimes, however, they may have more chronic infections, an increased frequency of atopy and asthma, as well as autoimmune diseases like rheumatoid arthritis. Selective IgA deficiency is associated with an increased risk of some malignancies, like gastric and colon cancer.
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