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Immunoglobulins of type A (IgA) are the most important molecules in the specific immune response associated with mucous membranes. Thanks to their very high daily production, the body protects itself against the penetration of bacteria, viruses and food particles. Therefore, both deficiency and excess of IgA antibodies may indicate an ongoing pathology.

Type A immunoglobulins (IgA)or type A antibodies are immune proteins produced by cells of the immune system - plasma cells, which are a type of B lymphocytes. exposure to various chemical molecules (antigens) that the immune system recognizes as foreign.

Antigens can be fragments of bacteria, viruses, fungi, food, pollen, and in some situations the body's own tissues (so-called autoantigens).IgA antibodiesact specifically as they are always directed against a specific antigen.

Immunoglobulin type A (IgA) - role in the body

Although the concentration of IgA antibodies in the blood is low (1.4-4 mg / ml), the body produces more of them than all the other antibodies put together. This is due to the fact that IgA antibodies are mainly secreted by the mucous membranes and are found in secretions (tears, saliva).

Daily IgA antibody synthesis can be up to 9 grams per day. Due to this, the IgA antibody is one of the main defense elements of mucous membranes against environmental antigens.

The task of the IgA antibody is to inhibit the adherence of bacteria to the surface of mucous membranes and their sticking, neutralization of viruses, toxins, enzymes secreted by bacteria and food antigens.

Immunoglobulin type A (IgA) - types

IgA antibodies can be divided into total and specific. Specific IgA antibodies are produced throughout life by the body after contact with various antigens. All the specific IgA antibodies in the body constitute the pool of total IgA. Testing specific IgA antibodies is of particular importance in the diagnosis of some autoimmune diseases, e.g. celiac disease.

IgA antibodies, due to the differences in the molecular structure, have been additionally divided into two subtypes:

  • IgA1, which is about 80 percent. of all IgA in the blood is longerand sensitive to bacterial enzymes
  • IgA2, which is about 20 percent. of total IgA in the blood, it is shorter and therefore more resistant to the action of bacterial enzymes; occurs mainly in the digestive tract

On the surface of the mucous membranes and in the secretions, the IgA antibody is also present in the form related to the so-called secretory fragment. The antibody is then called secretory IgA (sIgA). sIgA is also found in small amounts in the blood, accounting for 5-10 percent. IgA antibodies.

Immunoglobulin type A (IgA) - indications for the test

  • suspected hereditary immunodeficiencies of genetic background, e.g. selective IgA deficiency
  • suspicion of secondary immunodeficiencies e.g. AIDS
  • suspicion of cirrhosis
  • suspected autoimmune disease, e.g. rheumatoid arthritis, celiac disease
  • suspicion of hematological neoplasms, e.g. multiple myeloma, lymphomas
  • suspected IgA-associated nephropathy
  • chronic diarrhea
  • chronic respiratory infections

Tissue-specific IgA testing is a marker of the ongoing autoimmune process. An example is celiac disease, in the course of which high levels of IgA antibodies to tissue transglutaminase (anti-tTG) are a diagnostic marker of this disease.

Immunoglobulin type A (IgA) - what is the test?

In laboratory tests, we can assess the concentration of both total and specific IgA antibodies. Both tests can be performed with venous blood and, in special clinical cases, with feces or saliva.

The concentration of specific IgA antibodies is most often determined using enzyme immunoassay methods (eg ELISA test) or immunofluorescence methods. The immunonephelometric and immunoturbidimetric methods are also routinely used to determine total IgA antibody levels.

  • Type G immunoglobulin (IgG)
  • Type E immunoglobulins (IgE)
  • Type M immunoglobulins (IgM)
Worth knowing

Immunoglobulin type A (IgA) - norm

Laboratory norms for total IgA are age dependent and are:

  • 1-7 days: less than 0.06 g / l
  • 8 days-2 months: less than 0.06-0.07 g / l
  • 3-5 months: less than 0.06-0.77 g / l
  • 6-9 months: 0.065-0.52 g / l
  • 10-15 months: 0.07-0.45 g / l
  • 16-24 months: 0.13-0.93 g / l
  • 2-5 years: 0.1-1.33 g / l
  • 5-10 years: 0.38-2.35 g / l
  • 10-14 years: 0.62-2.3 g / l
  • 14-18 years old:0.85-1.94 g / l
  • over 18 years old: 0.52-3.44 g / l

Immunoglobulin type A (IgA) - results. What does elevated level mean?

Increased level of IgA antibodies is observed in:

  • chronic inflammations (especially those related to mucous membranes)
  • cirrhosis of the liver
  • AIDS
  • autoimmune diseases, e.g. celiac disease
  • hematological diseases, e.g. multiple myeloma, lymphomas

Immunoglobulin type A (IgA) - results. What does low level mean?

Decreased IgA antibody levels are seen in:

  • primary immunodeficiencies e.g. hyper-IgM syndrome, Bruto's disease
  • respiratory diseases, e.g. bronchial asthma, recurrent respiratory infections
  • infectious diseases, e.g. Epstein-Barr virus infection
  • diseases of the gastrointestinal tract, e.g. chronic diarrhea, chronic liver diseases
  • autoimmune diseases, e.g. type 1 diabetes
  • skin diseases, e.g. atopic dermatitis
  • diseases with a genetic background, e.g. Down syndrome
  • Protein Loss or Malabsorption Syndrome
  • taking medications such as phenytoin, gold s alts, non-steroidal anti-inflammatory drugs

Immunoglobulin type A (IgA) - selective IgA deficiency

Selective IgA Deficiencyis the most common primary (genetic) immunodeficiency with normal levels of other classes of antibodies (IgG, IgM).

It occurs in 1: 500 inhabitants of Europe, while in Asia, such as China or Japan, it occurs much less frequently.

Selective IgA deficiency is asymptomatic or mildly recurring respiratory tract infections in most people, mainly caused by viruses.

It has been shown that people with selective IgA deficiency are more likely to develop allergic and autoimmune diseases, such as:

  • celiakia
  • type 1 diabetes
  • juvenile idiopathic chronic arthritis
  • vitiligo
  • inflammatory bowel diseases such as ulcerative colitis
  • hemolytic anemia
  • systemic lupus erythematosus

Such predisposition in people with selective IgA deficiency may result from overloading the mucous membranes with antigens, which cannot be effectively neutralized by the deficiency of IgA antibodies, and as a consequence of chronic inflammation.

In addition, it has been observed that IgA deficiency and some autoimmune diseases canhave a common genetic basis (HLA histocompatibility polymorphisms).

Immunoglobulin type A (IgA) - IgA-associated nephropathy

IgA-related nephropathy (akaBerger disease ) is an inflammatory disease of the glomeruli where there is a buildup of IgA antibodies in the mesangium (a type of connective tissue in the kidney).

One of the symptoms of the disease is hematuria and arterial hypertension. The development of the disease is favored by genetic predisposition, but it also accompanies various diseases such as rheumatoid arthritis, psoriasis or celiac disease.

The diagnosis of IgA-associated nephropathy is performed by submitting a tissue section from the kidney to immunofluorescence or immunohistochemistry to confirm the presence of IgA deposits.

References

  1. Lewandowicz-Uszyńska A. et al. IgA deficiency - should you be afraid of it? Post-Diploma Pediatrics, 2013, 1.
  2. Czyżewska-Buczyńska A. et al. IgA an important element of the immune system - selected issues. Postepy Hig Med Dosw, 2007, 61, 38-47.
  3. Paul W.E. Fundamental immunology, Philadelphia: Wolters Kluwer / Lippincott Williams & Wilkin 2008, 6th edition.
  4. Laboratory diagnostics with elements of clinical biochemistry, a textbook for medical students edited by Dembińska-Kieć A. and Naskalski J.W., Elsevier Urban & Partner Wydawnictwo Wrocław 2009, 3rd edition
  5. Internal diseases, edited by Szczeklik A., Medycyna Praktyczna Kraków 2010
About the authorKarolina Karabin, MD, PhD, molecular biologist, laboratory diagnostician, Cambridge Diagnostics Polska A biologist by profession, specializing in microbiology, and a laboratory diagnostician with over 10 years of experience in laboratory work. A graduate of the College of Molecular Medicine and a member of the Polish Society of Human Genetics. Head of research grants at the Laboratory of Molecular Diagnostics at the Department of Hematology, Oncology and Internal Diseases of the Medical University of Warsaw. She defended the title of doctor of medical sciences in the field of medical biology at the 1st Faculty of Medicine of the Medical University of Warsaw. Author of many scientific and popular science works in the field of laboratory diagnostics, molecular biology and nutrition. On a daily basis, as a specialist in the field of laboratory diagnostics, he runs the content department at Cambridge Diagnostics Polska and cooperates with a team of nutritionists at the CD Dietary Clinic. He shares his practical knowledge on diagnostics and diet therapy of diseases with specialists at conferences, training sessions, and in magazines and websites. She is particularly interested in the influence of modern lifestyle on molecular processes inthe body.

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Immune system