Immunoglobulin A (IgA)

Sample

1. The patient’s serum is needed for the estimation of IgA.
2. A random sample can be taken.
3. Analyzed a fresh sample or store at 4 °C for less than 72 hours. Stable for 6 months at -20 °C.
4. Avoid lipemic or hemolyzed serum.

Indications for Immunoglobulin A (IgA)

1. IgA level is advised in the suspected case of its deficiency.
2. In case of repeated infections of the sinuses, respiratory system, and GIT.

Factors influencing the result:

1. Drugs that will increase the values are:
   1. Hydralazine.
   2. Phenytoin.
   3. Isoniazid (INH).
   4. Procainamide.
   5. Tetanus toxin and toxoid.
   6. Therapeutic gamma globulins.

Pathophysiology of Immunoglobulin A (IgA)

1. IgA is the second most common Ig, and it has two subclasses:
   1. IgA 1
   2. IgA2
   3. It is 15%  to 20% of the total Ig.
   4. It has a half-life of 6 days.
   5. It has paired kappa (κ) or lambda (λ) chains,
   6. Two heavy chains.
2. IgA consists of two monomers joined by J-chain and secretory fragments.
   1. IgA monomer form is found in high concentrations in the serum (90 to 450 mg/dL in a normal adult).
3. IgA antibodies are produced by the plasma cells.
4. The plasma cells are derived from activated B – lymphocytes.
5. The presence of IgA secretion is present In:
   1. IgA antibodies are found in the digestive system, respiratory system, colostrum, milk, nose, eyes,  and vagina.
      1. IgA is also found in saliva, tears, and blood.
6. Immunoglobulins are present in the γ and β-region on the electrophoresis.
   1. IgG migrates in the area between the β-region and γ-region.
   2. IgA migrates in the pregamma region and some portion in the γ-region.
   3. IgM is also present in the pregama and γ-region.

Immunoglobulin A (IgA): Immunoglobulins electrophoresis pattern

The normal structure of IgA

1. IgA consists of a dimer structure.
2. There is a J-chain that joins the two molecules of immunoglobulins.
3. Also, there is a secretory piece.

Immunoglobulin A (IgA): IgA structure

Immunoglobulin A (IgA): IgA structure with a secretory piece

Functions of IgA

1. IgA antibody’s main function is to protect the mucosa exposed to various antigens.
2. It can activate complement by alternative pathways.
3. It is an effective opsonin.
4. The secretory IgA consists of two 4- basic chain units (dimeric form), joined by the J-chain.
5. The deficiency of IgA leads to infection of the gastrointestinal and respiratory systems.
6. It has antiviral activity.
7. Its major role is the protection of bacteria, viruses, and protozoal infection by preventing their attachment and colonization to the mucosa.

Normal IgA level

Source 1

• To convert into SI unit x 10 = mg/L

Source 2

• Adult = 85 to 385 mg/dL
• Children = 1 to 350 mg/dL

Another source

• 0 to <5 months = 7.0  to  37.0 mg/dL
• 15 to <24 months =  36  to  79 mg/dL
• 2 to <4 years =  27 to  246 mg/dL
• 10 to <13 years =  42 to  295 mg/dL
• 16 to <18 years =  60 to 337 mg/dL
• more than 18 years = 61 to  356 mg/dL

The increased level of IgA is seen in:

1. Multiple Myeloma
2. Cirrhosis of liver
3. Systemic lupus erythematosus
4. Rheumatoid arthritis
5. Sarcoidosis
6. Wiskott-Aldrich syndrome

The decreased level of IgA is seen in:

1. Hereditary telangiectasia
2. Type 111 dysgammaglobulinemia
3. Malabsorption in some cases
4. Occasional cases of Cirrhosis of liver
5. Occasional cases of SLE
6. Occasional cases of Still’s disease
7. Occasional cases of recurrent otitis media
8. In Agammaglobulinemia
9. Hereditary thymic aplasia
10. Waldenstrom macroglobulinemia
11. Non-IgA myeloma
12. Acquired immune deficiency syndrome (AIDS)