Introduction to Immunology and Serology
Overview
Immunology is the study of the immune system and its responses. Serology is a laboratory discipline concerned with detecting or characterizing antibodies, antigens, and other immune-related markers in biological specimens.
Serological testing can support diagnosis, screening, surveillance, assessment of immune responses, and investigation of infectious or immune-mediated conditions.
Antigens and antibodies
An antigen is a substance or molecular structure that can be recognized by components of the immune system.
An antibody, or immunoglobulin, is a protein produced by B-cell-derived plasma cells that recognizes a particular antigenic target.
Different immunoglobulin classes have different biological characteristics. The laboratory significance of detecting an antibody depends on the assay, target, timing, and clinical context.
Common serological approaches
Depending on the examination, laboratories may use:
- Agglutination
- Enzyme immunoassays
- Chemiluminescent immunoassays
- Immunochromatographic methods
- Immunofluorescence
- Immunoblot-based methods
- Other validated immunochemical techniques
The analytical principle and performance characteristics are specific to the assay.
Qualitative and quantitative results
Serological tests may report:
- Detected / not detected
- Reactive / non-reactive
- Positive / negative
- A quantitative concentration
- A signal-to-cutoff or related index
- A titer or dilution-based result
The reporting terminology and decision criteria should follow the validated method.
Timing matters
Antigen and antibody detection can vary during the course of an infection or immune response. A negative result may therefore have different implications at different times.
Interpretation should consider:
- Time since exposure or symptom onset
- Test target
- Assay sensitivity and specificity
- Specimen type
- Patient population
- Pre-test probability
- Confirmatory or follow-up testing when indicated
Quality considerations
Serology requires appropriate controls, reagent storage, instrument performance where applicable, and adherence to the manufacturer's and laboratory's validated procedure.
Key points
- Immunology studies immune responses.
- Serology detects or characterizes immune-related markers.
- Different assays detect different targets and use different analytical principles.
- Timing and clinical context can affect interpretation.
- A static positive/negative rule should not replace assay-specific interpretation.
References
- NCBI. MeSH: Immunology.
- NCBI. MeSH: Serology.
- ISO 15189:2022. Medical laboratories — Requirements for quality and competence.