Types of Agglutination in Immunology

Agglutination Types

• Passive Agglutination: Involves insoluble particles attached to any antigen (viral, CRP, hormones, drugs).

• Common insoluble particles: latex, colloidal substances, charcoal, gelatin, resin beads, and RBCs.

• Reverse Passive Agglutination: Insoluble particles are coated with antibodies for detection.

• Coatable particles include colloidal latex, charcoals, gelatin, resin beads, and RBCs.

• Co-agglutination and Liposome-Enhanced Testing: Variations involving antigens bound to particles like liposomes, which increase visibility but can cause false results due to non-specific aggregation.

Immunologic Assays with Latex Particles

• Tests performed via latex particle agglutination include:
  • C-reactive protein
  • Immunoglobulin G rheumatoid factors
  • Immunoglobulin M rheumatoid factors
  • Rubella antibodies (currently using ELISA).

Human Chorionic Gonadotropin (hCG)

• A glycoprotein hormone secreted by the trophoblast of the developing embryo.
• Peak levels occur 2 to 3 months after the last menstrual period (LMP).
• Composed of two subunits: α (common in various hormones) and β (unique to hCG).
• Rapidly increases in urine or serum during early pregnancy.
• Use of monoclonal antibodies targeting the β-subunit enhances specificity.

Pregnancy Testing Protocols

• Principle: Latex particles coated with anti-hCG antibodies detect hCG in urine.

• Specimen Requirements:

  • First morning urine for highest hormone concentration.
  • Specific gravity should be at least 1.018.
  • Samples can be refrigerated for up to 2 days or frozen at -20°C for at least 1 year.

• Positive Results:

  • Technical errors can affect results; reagents should not be expired.
  • Latex reagent must be well shaken, and agglutination readings should be made within 3 minutes.

False Results

• False-Negative: Can occur if testing is done before detectable hCG levels or with low urine concentration; serum samples may be needed.
• False-Positive: Can arise from using monoclonal antibodies against α units or after hCG injections for ovulation.

Factors Affecting Test Quality

• Incubation time with the antibody source and the quality and amount of the antibody conjugated to the carrier significantly influence results.
• Secondary antibodies can enhance agglutination.

Mechanisms of Agglutination

• Agglutination involves sensitization (Ag-Ab reaction) followed by lattice formation (aggregation through cross-linking).
• Factors influencing sensitization include particle charge, antibody type, Ag-Ab ratio, antigenic determinants, pH, and temperature.

Methods to Enhance Agglutination

• Techniques include using low ionic strength saline, proteolytic enzymes, colloids, and antihuman globulin.

Graded Agglutination Reactions

• Pseudoagglutination: False appearance of clumping may occur when particles aggregate nonspecifically.

Microplate Agglutination Reactions

• Allows testing of large samples on a single plate, optimizing time and efficiency by bypassing labeling test tubes.
• Typically uses U-shaped microplates in immunohematology, which are centrifuged for immediate reading.

Summary on Immunoassays

• Immunoassays involve antibody-antigen interactions.
• Precipitation Reactions: Soluble antigens and antibodies form insoluble products, with various techniques such as double gel diffusion, radial immunodiffusion, and more for detection.

This quiz covers various types of agglutination, focusing on passive and reverse passive agglutination. Participants will learn about the role of different particles and antibodies in these processes. Test your knowledge on how these agglutination methods are applied in immunological contexts.