Immune Status

Q: Which cells and humoral factors belong to the innate branch of immunity?

The innate branch of immunity includes: Cellular elements: phagocytes, including macrophages, and NK cells;Humoral factors: complement system, antimicrobial peptides (lysozyme, α-defensins, cathelicidins), cytokines, and chemokines.

For medical students3 min readUpdated 2026-10-10

Immune status is a comprehensive characteristic of the immune system's functional state, determined through a set of quantitative and qualitative clinical and laboratory tests. Proper evaluation of this status is essential for diagnosing immunopathologies, monitoring disease progression, and tailoring personalized therapy.

Main materialPeripheral blood, its plasma, serum, and isolated cells.

Primary methodFlow cytometry for counting lymphocyte subpopulations using CD markers.

Allergy markerSharp increase in the concentration of immunoglobulin E (IgE) classes.

CD19 dynamicsThe count of B lymphocytes (CD19) in the blood naturally decreases with age.

Assessment Algorithm and Objects of Study

The diagnosis of immune disorders relies on a clear algorithm: first, an immunological history is taken, followed by laboratory investigation of key immune components, and finally, a specific pathology is verified. Laboratory testing employs a tiered (two-stage) approach.

All tests are classified according to cellular and humoral targets:

Cellular branch of adaptive immunity: T-lymphocyte populations are analyzed.
Humoral branch of adaptive immunity: B-lymphocyte status and antibody (immunoglobulin) concentrations are evaluated.
Cellular branch of innate immunity: The activity of macrophages (phagocytes), NK cells, and other factors is investigated.
Functional molecules: The levels of cytokines and other soluble mediators are determined.

The primary biological material is peripheral blood. In complex cases, additional materials are used: mucous membrane secretions, tear fluid, and cerebrospinal fluid (liquor).

Age-Related Dynamics of Parameters

The main tool for studying cell populations is flow cytometry. This method evaluates 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 dependencies, as reference values are not static. For example, during the transition from preschool age to adulthood, 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 share 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 branch, 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 antibody classes (such as IgE) are normally virtually undetectable in the bloodstream. A sharp increase in IgE serves as a reliable marker for allergic pathology.

It is important to remember that parameters have a wide range of normal values. They vary significantly under the influence of hormonal shifts, environmental factors, and other causes, which can make interpretation difficult. During analysis, the physician typically concludes one of three states: no reliable changes, minor shifts in several parameters, or significant alterations in immune status.

Advanced Evaluation of Immune Response Stages

If basic tests are insufficient, an expanded immunogram is used, detailing the performance of protective systems at all stages of the process:

Antigen recognition: T-helper function is evaluated (expression of MHC II molecules), quantitative analysis of CD4+ and CD8+ cells is performed, and activation markers (expression of CD25, CD69, synthesis of pro-inflammatory cytokines) are identified.
Differentiation: Identification of specific CD markers at various stages of lymphocyte maturation.
Effector phase: Analysis of cellular cytotoxicity and the production of effector molecules.
Immune memory: Determination of specific immunoglobulin levels.
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 (via the TUNEL method).

Personalized Diagnostics and Therapy

Ordering a full panel of immunological tests is excessive; test selection must always be based on the clinical picture. This differential approach optimizes diagnostics:

In bacterial infections, it is appropriate to examine the B-cell branch of immunity.
In viral infections, the emphasis shifts to the cellular branch (innate and adaptive), as well as the interferon status.

Obtained laboratory data allow specialists to precisely select immunotropic therapy and minimize the risk of side effects for the patient.

Frequently asked questions

What specific laboratory tests are included in the first (screening) stage of two-tiered immune status evaluation?

The first stage of immune status evaluation includes screening tests to identify pronounced disorders. These include:

Leukocytes — absolute and relative counts;
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 evaluate the functional activity (engulfment and bactericidal capacity) of phagocytes?

Microscopic and modern instrumental methods are used to evaluate phagocytic functional activity. To assess phagocytic (engulfment) activity:

Traditional method — microscopic evaluation of stained smears with microorganisms or inert particles;
Modern method — flow cytometry using fluorochrome-labeled phagocytosis objects.

To assess bactericidal capacity:

Completed phagocytosis test — determining the degree of reduction in the number of microorganisms cultured from phagocyte lysates;
NBT test — nitroblue tetrazolium reduction assay.

Which 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 evaluated. Pro-inflammatory 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 factored into the balance assessment.

Which cells and humoral factors belong to the innate branch of immunity?

The innate branch of immunity includes:

Cellular elements: phagocytes, including macrophages, and NK cells;
Humoral factors: complement system, antimicrobial peptides (lysozyme, α-defensins, cathelicidins), cytokines, and chemokines.

Is it always necessary to order an expanded immunogram for a patient?

No, performing a full panel of immunological tests is most often redundant. The choice of specific parameters to analyze is strictly based on the patient's clinical presentation.

How does the lymphocyte count change as a person matures?

Age-related dynamics vary: the relative number of T cells (markers CD3, CD4, CD8) increases with age, whereas the percentage of B lymphocytes (CD19), conversely, decreases.

Which branches of immunity should be prioritized during infectious diseases?

When bacterial infections are suspected, the B-cell branch should be investigated. In viral infections, evaluating cellular immunity and interferon status is of key importance.

What method is considered primary for counting lymphocyte subpopulations?

The key method is flow cytometry. It allows for accurate assessment of the absolute and relative quantities of cells based on specific CD markers on their surface.

Go deeper

Antigen recognition mechanisms and MHC II molecule functions
Balance of pro- 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 method