Structure and biologic functions of IgA
- Leman Yel, MD
Leman Yel, MD
- Associate Professor Emeritus of Clinical Medicine
- University of California
Immunoglobulin A (IgA) is the most abundant type of antibody in the body, comprising most of the immunoglobulin in secretions and a significant amount of circulating immunoglobulin. In secretions, it serves to protect the mucosal tissues from microbial invasion and maintain immune homeostasis with the microbiota. The distribution, structure, production, biologic functions, and regulation of IgA will be discussed in this review.
Selective IgA deficiency is reviewed separately. (See "Selective IgA deficiency: Clinical manifestations, pathophysiology, and diagnosis" and "Selective IgA deficiency: Management and prognosis".)
Immunoglobulin A (IgA) is the most abundant antibody isotype in the body, comprising almost 70 percent of the body's total immunoglobulin. The majority of IgA is found in the various mucous secretions, including saliva, milk, colostrum, tears, and secretions from the respiratory tract, genitourinary tract, and prostate [1-3].
Normal serum levels — IgA is the second most abundant isotype in the circulation, following IgG [4-8]. IgA levels, generally absent at birth, gradually increase throughout the first year of life to about 30 percent of adult levels at one year. Adult levels of IgA are reached in adolescence . Normal serum levels range from 61 to 356 mg/dL .
Abnormal levels — Increased serum levels of IgA are seen in several inflammatory disorders, including IgA nephropathy, Henoch-Schönlein Purpura, AIDS, alcoholic cirrhosis, advanced hepatitis, IgA myeloma, and several autoimmune diseases (eg, rheumatoid arthritis, systemic lupus erythematosus).
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