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Blood Reactions, Blood Bank. Blood Reactions, ABO Groups
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Characteristics
• is the aggregation of particulate matter due
to combination with specific antibody.
• takes place on the surface of the particle
and thus antigen must be exposed and able
to bind with antibody
• Involve particulate antigens and antibodies
Characteristics cont’d
• types of particles participating in such reactions include:
erythrocytes, bacterial cells, and inert carrier such as
latex particles.
• antigen consists of suspensions of microorganisms, cells
(rbc) or uniform particles like latex
• Antigens may be:
– On a cell (direct agglutination)
– Attached to latex spheres (indirect or passive agglutination)
Characteristics cont’d
• Agglutination reaction is aided by elevated
temperature (37-56°C) and by:
– Movement which increases the contact between
antigen and antibody.
– Clear supernatant.
– Clumps aggregate and settle as large visible
clumps.
Agglutination Requirements
• Availability of stable cell or particle
suspension
• Presence of one or more antigens close to
the surface
• Knowledge that ‘incomplete’ or non-
agglutinating antibodies are not detectable
without modifications, e.g. antiglobulin
(Coomb’s) technic
Advantages
• Agglutination of insoluble native antigens or
antigen-coated particles simple to read with or
without the aid of a microscope.
• Increased degree of sensitivity
• Great variety of detectable substances
Steps in Agglutination
1. Sensitization
• involves antigen-antibody combination through
single antigenic determinants on the particle
surface
• may be affected by the nature of the antibody
molecules, affinity and avidity of individual
antibody, and the nature of antigen-bearing
surface
Steps in Agglutination Reaction
2. Aggregative Stage
represents the sum of interaction between antibody and
multiple antigenic determinants on a particle
dependent on environmental conditions as well as the
relative concentrations of antigen and antibody
it could be enhanced by LISS (Low ionic strength saline),
neutralizes surface charges and facilitates agglutination
(albumin 5 - 50%)
Uses of Agglutination Reactions
• Aid in the identification, by means of known antisera
(serum containing antibodies speciftic for a given
antigen), microorganisms cultured from clinical
specimens.
• Help estimate the titer of antibacterial agglutinins in
the serum of patients with unknown diseases.
Types of Agglutination Reactions
• Direct Agglutination
• Passive Agglutination
• Reverse Passive Agglutination
• Agglutination inhibition
• Hemagglutination-inhibition
• Coagglutination/Conglutination
Types of Agglutination Rxns.
• Direct agglutination - occurs when antigens are found
naturally on a particle (Serotyping of Salmonella)
– e.g. identification of bacterial types
• O antigen (somatic) - compact, fine and granular
agglutination
• H antigen (flagellar) - form a loosely woven network of
clumped cells (coarse and floccular), called snowflake
agglutination
• hemagglutination (agglutination reaction which involves
rbc)
Agglutination Reactions
• Passive agglutination - employs particles that are
coated with antigens not normally found on their
surfaces.
– Inert materials commonly used:
1. Bentonite 3. Colloidion
2. Latex particles 4. Colloidal charcoal
Agglutination Reactions
Reverse Passive agglutination - antibody rather than
antigen is attached to a carrier particle.
Agglutination inhibition - based on competition between
particulate and soluble antigens for limited antibody
combining sites, and a lack of agglutination is an indicator
of a positive reaction.
Hemagglutination inhibition reactions -tests the presence of
antibodies to certain viruses, such as rubella, mumps,
measles, influenza, and adenovirus
Hemagglutination Hemagglutination involves agglutination of RBCs.
Viral hemagglutination inhibition tests for antibodies by the
antibodies' ability to prevent viruses from agglutinating RBCs.
Figure 18.7
Agglutination Reactions
• Coagglutination/Conglutination - name given to
systems using bacteria as inert particles to which
antibody is attached (S. aureus).
– the Fc region of antibody attaches to protein A of
staphylococcal cell leaving the Fab region to combine with
the antigen
– killed staphylococcal cells coated with antibody can be used
to identify bacteria and detect soluble extracellular bacterial
antigens in specimens and body fluids.
Reading Agglutination Reactions Macroscopic +4 One solid aggregate or clump of cells.
+3 Several large aggregates, clear background.
+2 Small to medium sized aggregates, clear background.
+1 Small aggregates, turbid reddish background.
± Weak granularity in cell suspension. A few macroscopic agglutinates but
numerous agglutinates microscopically
MF Any degree of agglutination in a sea of unagglutinated cells
Hem Hemolysis is interpreted as a positive reaction and may be graded as
complete or partial; hemolysis and agglutination may be recorded on the
same tube.
Ø No agglutination, smooth reddish background
Microscopic: + Positive - aggregates of at least 3-5 cells. Ø Negative - no agglutination.