Assessment algorithm and study objects
The diagnosis of immune disorders is based on a clear algorithm: first, an immunological history is taken, then a laboratory study of key components of the immunity is conducted, and finally, a specific pathology is verified. A tiered (two-stage) approach is used for laboratory tests.
All studies are classified by cellular and humoral targets:
- Cellular arm of adaptive immunity: T lymphocyte populations are analyzed.
- Humoral arm of adaptive immunity: the state of B lymphocytes and the concentration of antibodies (immunoglobulins) are assessed.
- Cellular arm of innate immunity: the activity of macrophages (phagocytes), NK cells, and other factors is investigated.
- Functional molecules: the level of cytokines and other soluble mediators is determined.
The main biological material is peripheral blood. In complex cases, additional material is utilized: mucous membrane secretions, tear fluid, and cerebrospinal fluid (CSF).
Age-related dynamics of parameters
The main tool for studying cellular populations is flow cytometry. This method allows for the assessment of absolute and relative (percentage ratio) parameters of cells carrying specific receptors—CD markers—on their surface.
When interpreting results, it is important to consider age-related dependence, as normative values are not static. For example, during the transition from preschool to adult age, the following pattern is observed:
- T lymphocytes (CD3): relative count increases from 62–69% (up to 6 years) to 66–76% in adults.
- T helper cells (CD4): the population increases from 30–40% (up to 17 years) to 38–46%.
- Cytotoxic T lymphocytes (CD8): their proportion smoothly increases from 25–32% to 31–40%.
- B lymphocytes (CD19): unlike T cells, their count gradually decreases from 24% in childhood to 13% in adulthood.
Humoral immunity and its variability
To assess the humoral arm, the concentration of major immunoglobulin classes in blood serum is determined. In healthy adults, reference values are:
- IgG: 6.5–13.5 g/L;
- IgM: 0.55–3.5 g/L;
- IgA: 0.7–3.15 g/L.
Other classes of antibodies (e.g., IgE) are practically undetectable in the bloodstream under normal conditions. A sharp increase in IgE serves as a reliable marker for the development of allergic pathology.
It is important to remember that indicators have a wide normal range. They vary significantly under the influence of hormonal shifts, environmental factors, and other causes, which can make interpretation difficult. When analyzing, a physician typically notes one of three states: no significant changes, a slight shift in several parameters, or significant changes in the immune status.
In-depth assessment of immune response stages
If basic tests are insufficient, an expanded immunophenotyping profile (immunogram) is used, detailing the functioning of defense systems at all stages of the process:
- Antigen recognition: T-helper function is assessed (expression of MHC II molecules), quantitative analysis of CD4+ and CD8+ cells is performed, and activation markers are identified (CD25, CD69 expression, synthesis of proinflammatory cytokines).
- Differentiation: identification of specific CD markers at various stages of lymphocyte maturation.
- Effector phase: analysis of cellular cytotoxicity and production of effector molecules.
- Immune memory: determination of the level of specific immunoglobulins.
- Immunoregulation: assessment of the balance of pro- and anti-inflammatory cytokines, determination of regulatory T cells (T-reg).
- Apoptosis: the final stage of the response, studied by assessing caspase activity and identifying apoptotic bodies (using the TUNEL method).
Personalized diagnostics and therapy
Prescribing the full spectrum of immunological studies is redundant—the choice of tests should always be based on the clinical picture. This differential approach optimizes diagnostics:
- In bacterial infections, it is advisable to study the B-cell arm of immunity.
- In viral infections, the focus is placed on the cellular arm (innate and adaptive), as well as the interferon status.
The obtained laboratory data allow the specialist to precisely select immunotropic therapy and minimize the risk of side effects for the patient.
Briefly: answers to topical questions
What specific laboratory tests are included in the first (screening) stage of the two-tier immune status assessment?
The first (screening) stage of immune status assessment includes screening tests to identify pronounced disorders. These include:
- Leukocytes — absolute and relative count;
- Lymphocytes — total count of T and B lymphocytes;
- NK cells — quantitative assessment;
- Immunoglobulins — total concentration of major classes;
- Phagocytes — assessment of leukocyte phagocytic activity.
What methods are used to assess the functional activity (engulfing and bactericidal capacity) of phagocytes?
Microscopic and modern instrumental methods are used to assess the functional activity of phagocytes. To assess phagocytic (engulfing) activity, the following are used:
- Traditional method — microscopic evaluation of stained smears with microorganisms or inert particles;
- Modern method — flow cytometry using objects of phagocytosis labeled with fluorochromes.
To assess bactericidal activity, the following are used:
- Phagocytosis completion test — determination of the degree of decrease in the number of microorganisms cultured from phagocyte lysate;
- NBT test — nitroblue tetrazolium reduction assay.
What specific interleukins are evaluated to determine the balance of pro- and anti-inflammatory cytokines?
To determine the balance, the levels of interleukins divided into two antagonistic groups are assessed. Proinflammatory interleukins include:
- IL-1;
- IL-6;
- IL-12;
- IL-17;
- IL-23.
Anti-inflammatory interleukins include:
- IL-10.
Other cytokines, such as tumor necrosis factor (TNF-α) and transforming growth factor beta (TGF-β), are also taken into account when assessing the balance.
Which cells and humoral factors belong to the innate arm of immunity?
The innate immune system includes:
- Cellular elements: phagocytes, including macrophages, and NK cells;
- Humoral factors: complement system, antimicrobial peptides (lysozyme, α-defensins, cathelicidins), cytokines, and chemokines.
Class and exam questions
Is it always necessary to prescribe a comprehensive immunogram to a patient?
No, ordering a full panel of immunological tests is usually redundant. The selection of specific parameters for analysis is strictly based on the patient's clinical presentation.
How does the number of lymphocytes change as a person grows older?
Age-related dynamics are multidirectional: the relative count of T cells (markers CD3, CD4, CD8) increases with age, whereas the percentage of B lymphocytes (CD19), conversely, decreases.
Which components of the immune system should be prioritized in infectious diseases?
When bacterial infections are suspected, the B-cell arm should be investigated. In viral infections, assessing cellular immunity and interferon status is of key importance.
What method is considered the primary one for counting lymphocyte subpopulations?
The key method is flow cytometry. It allows for accurate evaluation of absolute and relative cell counts based on specific CD markers on their surface.
What else to study on this topic
- Mechanisms of antigen recognition and functions of MHC II molecules
- Balance of pro-inflammatory and anti-inflammatory cytokines
- Role of regulatory T cells in immunoregulation
- Lymphocyte activation markers: significance of CD25 and CD69
- Molecular mechanisms of apoptosis and principles of the TUNEL assay
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