Blood immunoglobulins

Position of immunoglobulins among plasma proteins

Normally, the total plasma protein concentration is 60–80 g/L. Albumin accounts for 40–60 g/L of this amount, and globulins account for 20–30 g/L. To study the composition in detail, paper electrophoresis is used. In an electric field, proteins are separated into five fractions depending on their charge and mass.

Immunoglobulins (classes IgA, IgD, IgE, IgG, IgM), which are responsible for humoral immunity, form the γ-globulin fraction. It accounts for 12–22% of all plasma proteins. Due to their physicochemical properties, this group has the lowest electrophoretic mobility.

The remaining fractions are distributed as follows:

• Albumin (55–65%): has the highest mobility. Synthesized in the liver, maintains oncotic pressure, and transports ligands and calcium ions (Ca2+).
• α1-globulins (2–4%): high-mobility fraction. Includes α1-antitrypsin, prothrombin, and high-density lipoproteins (α1-HDLs).
• α2-globulins (6–12%): moderate mobility. This fraction contains α2-macroglobulin, ceruloplasmin, plasminogen, and haptoglobin.
• β-globulins (8–12%): low mobility. Includes fibrinogen, transferrin, and low-density lipoproteins (β-LDLs).

Any disturbance in the normal ratio of these fractions (hyperproteinemia, hypoproteinemia, or paraproteinemia) is called dysproteinemia.

Changes in immunoglobulin levels in pathologies

Assessing the expression of molecules of various classes and subclasses of immunoglobulins is a crucial step in the diagnosis of primary immunodeficiencies. These severe disorders present with specific shifts in the protein profile, while the functions of the lymphocytes themselves are sharply impaired in most cases.

Let us examine typical changes using the most common pathologies as examples:

• IgG fraction: levels drop in Bruton's agammaglobulinemia, common variable immunodeficiency, and hyper-IgM syndrome. However, in chronic granulomatous disease, the level of this immunoglobulin increases instead.
• IgM fraction: concentration decreases in Bruton's disease and common variable immunodeficiency. Meanwhile, a pathological elevation of IgM serves as a marker for hyper-IgM syndrome, hyper-IgE syndrome, ataxia-teleangiectasia, and chronic granulomatous disease.
• IgA fraction: its deficiency occurs in isolation (selective IgA deficiency) and also accompanies Bruton's syndrome, ataxia-teleangiectasia, hyper-IgM syndrome, and common variable immunodeficiency. An elevated IgA level is characteristic of Wiskott-Aldrich syndrome.

Regardless of the nature of the lesion and the specific molecular target, the significance of these diseases in medical practice is determined by their clinical manifestations, which are always rooted in the immunodeficiency itself.

Laboratory research methods and genetic screening

For an in-depth study of blood plasma proteins and the isolation of immunoglobulins in laboratory practice, methods of separating mixtures based on physicochemical properties are used. In addition to electrophoresis, the following are employed:

• Salting out: the process of reversible protein precipitation by salts as their concentration increases. Ammonium sulfate is most commonly used for this purpose.
• Gel filtration: a method of separating molecules by their mass using Sephadex beads. Smaller molecules are retained in the pores of the beads longer, so they emerge from the column later than larger ones.
• Dialysis: the procedure for removing low-molecular-weight impurities (such as salts) through a special semipermeable membrane.
• Precipitation with trichloroacetic acid (TCA): the primary reagent used for complete protein precipitation and removal to obtain a protein-free filtrate.

If immunological analysis reveals a defect (e.g., the absence of membrane CD154 on activated T cells, which is characteristic of hyper-IgM syndrome), the diagnosis must be confirmed at the molecular genetic level.

Using polymerase chain reaction (PCR), specialists determine the exact localization and nature of mutations. These can be deletions, missense mutations, or single nucleotide substitutions. Damage is most frequently found in the γ(c), btk, Phox, ZAP-70, ATM, FOXP3, and Fas genes.

Class and exam questions

What else to study on this topic

• Changes in the number and function of T cells (CD4+ and CD8+) in primary immunodeficiencies.
• Nephrotic protein profile pattern: causes of albumin drop and α2-globulin increase.
• The working principle of Sephadex bead gel filtration.
• The role of the CD154 membrane marker in diagnosing hyper-IgM syndrome.
• Characteristics and functions of plasma α1-, α2-, and β-globulins.

Other topics in the "Additional Topics" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.