Agglutination refers to the reversible binding of an antibody to its specific antigen, resulting in the formation of large aggregates or clumps.
AGGLUTINATION - TERMS
Agglutinins:
These are antibodies that cause agglutination.
Agglutinogens:
These are antigens that cause agglutination.
Clumping of Red Blood Cells:
This is specifically referred to as hemagglutination.
Clumping of Non-Red Blood Cells:
This is generally just termed agglutination.
STAGES OF AGGLUTINATION
Stage 1:
Attachment: The binding of antibodies to antigens occurs, sensitizing the antigens. At this stage, the process is not visible.
Stage 2:
Visible Reaction: This concludes with visible agglutination.
TYPES OF AGGLUTINATION
Direct Agglutination:
The particle is the carrier of the antigen (e.g., Widal test for Salmonella typhi related to typhoid fever).
Direct Hemagglutination:
The antigen is present on the red blood cells (e.g., ABO blood testing).
Passive Agglutination:
In this method, antigens are added to carrier molecules (e.g., latex beads, gelatin, charcoal).
Reverse Passive Agglutination:
This involves antibodies attached to carrier molecules.
Agglutination Inhibition:
No agglutination indicates a positive reaction (e.g., drug testing for cocaine/heroin, rubella).
Flocculation:
Where antibody detection occurs when soluble antigen interacts, forming a precipitin and resulting in fine particle precipitation in confined spaces.
AGGLUTINATION DEFINED
Agglutination Definition:
Agglutination can occur when either the antigen or the antibody is particulate (i.e., in the form of a particle or a cell).
Example:
An example of this is the ABO blood type, where the A antigen can be agglutinated by specific antibodies.
TYPES OF AGGLUTINATION CONTINUED
Reverse Agglutination:
discusses methods where antibodies are attached to carrier residues.
Co-agglutination:
Main example is a latex agglutination kit for rapid identification of Staphylococcus aureus, where the bacterium itself is identified as the antigen.
Hemagglutination:
Involves RBCs as the carriers.
AGGLUTINATION INHIBITION
Definition:
Agglutination inhibition, or neutralization, refers to agglutination being prevented in positive reactions. This occurs because the antigen from the patient is neutralized by the antisera (antibodies present in the kit). Should the RBCs be utilized as indicator cells, this will be termed hemagglutination inhibition.
HEMAGGLUTINATION INHIBITION - MECHANISM
Example Mechanism:
Patient sample with IgG expressing G1 epitope: No agglutination ensues when available anti-G1 epitope antibodies are bound by free G1-expressing antibodies in the sample serum, indicating a positive reaction.
Conversely, when IgG with an irrelevant heavy chain isotope is present, agglutination occurs, resulting in a negative reaction for hemagglutination inhibition.
CO-AGGLUTINATION
Definition:
Co-agglutination refers to the process where an antigen is a bacterial or viral cell.
Application Example:
An example includes the latex agglutination kit used for rapidly identifying Staphylococcus aureus.
FLOCCULATION
Principle of VDRL and RPR:
Utilizes cardiolipin antigen, with the RPR test attaching cardiolipin to charcoal particles for macroscopic visualization, primarily in the context of venereal disease testing.
PRECIPITATION - DEFINED
Definition:
Precipitation is defined as the reversible binding of a soluble antibody to its specific soluble antigen, forming insoluble aggregates that fall out of the solution.
Characteristics:
Both antigen and antibody must be soluble; when combined, they generate an insoluble complex that precipitates out of the solution.
PRECIPITATION TECHNIQUES
Types of Techniques:
Immunoelectrophoresis: Involves separation and identification via electrophoresis.
Immunodiffusion / Turbidimetric/Nephelometric techniques: Inclusive of several methodologies like double diffusion (Ouchterlony) and radial immunodiffusion.
IMMUNODIFFUSION TECHNIQUES
Double Diffusion (Ouchterlony):
This involves the diffusion of both soluble antigen and antibody in a porous support medium towards each other, forming a precipitation line (arc).
Radial Immunodiffusion (RID):
Soluble antigen is dissolved in an agarose gel, and when corresponding antibody diffuses from a well, a circular precipitation ring emerges when the optimal ratio for antigen and antibody occurs.
ISOELECTRIC FOCUSING - DEFINITION
Description:
Is electrophoresis of serum proteins to their isoelectric point (pI), where at the given pH, proteins display no charge, thus halting their movement in the electric field.
TURBIDIMETRY METHODS
Description:
Turbidimetry quantifies the cloudiness of a solution; as turbidity increases, the light transmitted decreases, indicating the concentration of solutes inversely proportionate to the percentage transmittance (%T).
NEPHELOMETRY - DESCRIPTION
Explanation:
Measures light scattered in a forward direction by particles in a solution, where concentration correlates with the forward light scatter detected at a 10 - 70 degrees angle.
LABELED TECHNIQUES
Types:
Radioimmunoassay (RIA): Rare nowadays, it utilizes radioactive labeling, commonly with radioactive iodine.
Enzyme Immunoassay (EIA): Employs enzyme reactions generating color changes based on antigen presence.
Immunofluorescent Assays (IFA): Use fluorescent substances, either indirectly or directly.
COMPETITIVE PROTEIN BINDING - PRINCIPLE
Concept:
Labeled antibody competes with an unlabeled antibody (derived from the patient) for binding sites on a known amount of antigen attached to a solid phase. This is pivotal in determining substance concentrations through competitive binding assays.
SANDWICH TECHNIQUE - PRINCIPLES
Explanation:
An unlabeled antigen from a kit attaches to the solid phase. Upon adding the patient sample, if antibody presence is noted, it binds to the antigen, followed by the addition of a labeled antigen. This forms a complex detectable based on the amount of labeling present.
FLOW CYTOMETRY - DEFINED
Definition:
Cells are suspended within a stream of fluid and pass through a laser light for detection, with both forward & side light scattered being analyzed for cell sorting based on internal components and surface markers, like CD4 and CD8 cell types.
MOLECULAR DIAGNOSTICS - DEFINITION
Description:
This involves utilizing RNA, DNA, or specific proteins for disease detection, with applications including PCR for DNA, RNA detection via PCR and microarrays, and proteins monitored through antibody-based methods for studying diseases such as breast cancer and autoimmune disorders like hepatitis and HIV/AIDS.