CLO3-immunodiagnostic techniques

IMMUNODIAGNOSTIC VET 2003 TECHNIQUES

1. SEROLOGY

1.1 Definition

  • Serology is the study of antigen–antibody binding in vitro.

  • Serologic tests detect antibodies produced by the patient against an infectious agent as part of the immune response.

1.2 Applications

  • Used to detect minute quantities of microbial antigen in samples.

  • Commonly looks for evidence of antibody specific for a microorganism, confirming exposure to that agent.

  • More refined tests can quantify the amount of specific antibodies, indicating stages of infection (e.g., IgG vs. IgM).

1.3 Importance in Diagnosis

  • One of the most common applications is diagnosing infectious diseases.

2. SEROLOGIC TESTS PRINCIPLE

  • Many tests use serum or plasma; other samples like saliva or fecal swabs are also usable.

  • Serologic testing using ELISA technology is increasingly available for in-clinic use.

3. ANTIBODY TITRE

3.1 Definition

  • The titre of an antibody indicates the level of specific antibody activity in a sample.

3.2 Measurement of Titre

  • Expressed as the reciprocal of the last positive serum dilution (e.g., a titre of 256 indicates a higher antibody level than 16).

4. ANTISERUM

4.1 Definition

  • Antiserum is serum collected from an animal exposed to a particular antigen, containing antibodies for that antigen.

4.2 Production

  • Typically produced by immunizing animals (e.g., mice, rabbits, sheep, goats) with the antigen of interest and collecting their serum.

4.3 Example of Production Process

  • Blood taken from a dog is used to extract dog IgG.

  • This IgG is injected into a rabbit to produce a rabbit anti-dog IgG antiserum.

5. SEROLOGIC TESTING TECHNIQUES

5.1 Types of Techniques

  • Agglutination

  • Precipitation

  • Complement Fixation Test (CFT)

  • Haemagglutination Inhibition (HAI)

  • Virus Neutralization (VN)

  • Immunofluorescent Antibody Test (IFA)

  • Enzyme-Linked Immunosorbent Assay (ELISA)

  • Immunochromatography

  • Western Blotting

5.2 Agglutination

  • A straightforward procedure for particulate antigens (e.g., RBCs, bacteria).

  • Antigen mixed with antibody to form agglomerations (agglutinates).

  • Example: Feline blood typing using agglutination for blood group identification.

5.3 Precipitation

  • Relies on antibodies to precipitate antigens in solution or agar gels, forming a lattice-like structure.

  • Commonly used for diagnosing some infectious diseases like fungal infections; agar gel diffusion (AGD) used to detect antibodies.

5.4 Haemagglutination Inhibition (HAI)

  • Used in virology, checks if virus particles agglutinate erythrocytes from specific animals.

5.5 Complement Fixation Test

  • Incubates serum with antigen; presence shows seropositivity by forming immune complexes.

5.6 Immunofluorescent Antibody Test (IFA)

  • Infectious agents spread on slides, serum added for binding if seropositive.

  • A secondary antiserum conjugated with a fluorochrome is applied for visualization under UV light.

5.7 Enzyme-Linked Immunosorbent Assay (ELISA)

  • Central technique in veterinary serology.

  • Two major forms:

    • Detects antibodies indicating past exposure.

    • Detects and quantifies antigens from active infections.

  • ELISA principles exploited in rapid in-house diagnostic tests like SNAP® technology.