Main groups of diagnostic methods
The spectrum of application of diagnostic preparations covers numerous analytical approaches that allow for a detailed study of the body's condition. The technical equipment for these methods ranges from basic manual tests (on a glass slide or in a test tube) to the use of complex computerized systems.
Key areas include:
- Antigen–antibody reactions. Both natural antigens and antibodies, as well as modern high-tech analogues, are used as reagents: monoclonal antibodies, synthetic peptides, and recombinant proteins.
- Molecular genetic studies. Include amplification-based genetic titrating (PCR) and molecular hybridization.
- Cellular reactions. Aimed at counting immunocompetent cells (antigen-presenting cells, T and B lymphocytes) and assessing their functional activity.
- Assessment of innate immunity factors. Analysis of the complement system, lysozyme levels, and interferons.
- Determination of soluble mediators. Measurement of cytokine concentrations and other substances regulating the immune response.
- Skin tests. A classic example of diagnostic reactions performed in vivo.
Fields of medical application
Modern diagnostic preparations have high sensitivity and specificity, making them more effective than endoscopic, radiological, or standard biochemical methods. They are actively used in several fields:
- Infectious diseases. These preparations are indispensable for identifying viral and bacterial agents. They are used to diagnose typhoid fever, plague, tularemia, anthrax, diphtheria, HIV infection, and viral hepatitis.
- Allergology. Identification of specific reactions to food, occupational, and other types of allergens.
- Oncology. Localization of malignant neoplasms, including lung, liver, and colorectal cancer.
- Transplantology. Determination of tissue compatibility, as well as early diagnosis of tolerance or graft rejection reactions.
- Obstetrics. Analysis of complex immunological relationships within the maternal-fetal system.
- Immune status monitoring. Identification of immunodeficient states and assessment of how adverse social or environmental factors affect the body's defense systems.
Biosensor test systems
A separate category consists of biosensor test systems. Their operation is based on registering chemical or physical changes that occur precisely at the moment a specific immune reaction takes place. These effects are detected by ultra-sensitive detectors.
- Physical parameters: detectors capture agglutination, opalescence, various types of radiation, or changes in the thermal background. For example, heat release during antigen-antibody binding can be recorded.
- Chemical parameters: systems record the formation of new compounds or reaction products. A characteristic example is the detection of released carbon dioxide ($CO_2$) during the interaction of an enzyme with its substrate when using enzyme labels.
The informational value of such systems is constantly increasing due to the introduction of purified antigens and monoclonal antibodies.
Briefly: answers to topical questions
Which classes of immunoglobulins are determined in blood serum to confirm the acute phase of an infectious disease?
To confirm the acute phase of an infectious disease, class M immunoglobulins, as well as early antibodies of other classes, are determined in blood serum. Identifying these markers helps clarify the phase of the process and distinguish an infectious disease from post-vaccination immunity.
- Class M immunoglobulins (IgM) — synthesized first in response to infection and serve as the main marker of the acute phase and primary infection.
- Class G immunoglobulins (IgG) — in the acute phase, they may be detected as low-avidity antibodies to pre-early proteins.
What classic skin tests (in vivo) are used to diagnose specific bacterial infections?
To diagnose bacterial infections, in vivo skin-allergy tests are used, based on detecting delayed-type hypersensitivity to a specific allergen. The following diagnostic preparations are used:
- Tuberculin (M. tuberculosis) — diagnosis of tuberculosis (Mantoux test).
- Brucellin — diagnosis of brucellosis (Burnet test).
- Tularin — diagnosis of tularemia.
- Lepromin — diagnosis of leprosy.
- Mallein — diagnosis of glanders.
- Anthraxin — diagnosis of anthrax.
- Pestin — diagnosis of plague.
The preparations are administered intradermally or percutaneously, and the result is evaluated after 48–72 hours by the presence and size of the infiltrate.
What tasks do diagnostic preparations solve in transplantology, and what methods are used to determine tissue compatibility?
In transplantology, diagnostic preparations are used to assess organ and tissue compatibility, as well as to diagnose rejection and tolerance reactions. To select a donor-recipient pair, MHC typing is performed using the following methods:
- Serological method — a microcytotoxicity test using B lymphocytes, monospecific sera, and complement.
- Molecular genetic method — DNA typing based on the polymerase chain reaction (PCR).
Modern PCR typing makes it possible to determine the MHC genes themselves rather than their protein products.
Class and exam questions
What is the main advantage of immunological diagnostic methods?
They possess significantly greater specificity and sensitivity compared to biochemical, endoscopic, and radiological examinations.
What modern reagents are used in antigen-antibody reactions?
In addition to natural components, monoclonal antibodies, recombinant proteins, and synthetic peptides are now widely used.
How do biosensor detectors work?
They record physical (heat, radiation, agglutination) or chemical (gas production, new products) effects that occur at the moment of a specific immune interaction.
What else to study on this topic
- Molecular genetic diagnostics: principles of PCR and hybridization
- Assessment of the functional state of T and B lymphocytes
- The role of cytokines as soluble mediators of the immune response
- Immunological aspects of transplantology and rejection reactions
- Innate immunity factors: complement system and lysozyme
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