SEROLOGY (PT1) (page 1-3)

serology

• the study of the fluid components in the blood, especially antibodies

serum

• liquid portion of the blood, minus the coagulation factors

• most frequently encountered specimen in immunologic testing

affinity

• initial force of attraction that exists between a single fab site on an antibody and a single epitope or determinant site on the corresponding antigen

• ag-ab binding is held together by weak noncovalent bonds and is therefore reversible. altering the physical conditions can release the antibody from the antigen-binding site

avidity

• sum of all the attractive forces between an antigen and an antibody

• strength with which a multivalent antibody binds a multivalent antigen

• measure of overall stability of an ag-ab complex

cross reactivity

• is caused by the presence of antigenic determinants that resemble one another so closely that antibody formed against one will react with the other

tube testing

• is considered more sensitive than slide testing because it allows more time for the ag-ab reaction

0

• no agglutinates

• dark, turbid, homogenous

w+

• many tiny agglutinates

• many free cells

• may not be visible without microscope

• dark, turbid

1+ (25%)

• many small agglutinates

• many free cells

• turbid

2+ (50%)

• many medium-sized agglutinates

• moderate number of free cells

• clear

3+ (75%)

• several large agglutinates

• few free cells

• clear

4+ (100%)

• one large solid agglutinate

• no free cells

• clear

elution

• procedure in which physical conditions are purposely manipulated to break the ag-ab complex, with subsequent release of the antibody into the surrounding medium

epitope

• antigenic determinant or determinant site

• key portion of immunogen

• molecular shapes or configurations that are recognized by b or t cells

paratope

• part of the antibody that binds to the epitope

pseudoagglutination

• false appearance of clumping which may be due to rouleaux formation

• to disperse this, add a few drops physiologic nacl to reaction tube, remix and re-examine

precipitation

• involves combination of soluble antigen with soluble antibody to produce insoluble complexes that are visible

zone of equivalence

• optimum precipitation occurs; number of multivalent sites of antigen and antibody are approximately equal

prozone

• excess antibody;

• false neg;

• remedy: serum dilution

post zone

• excess antigen;

• false neg;

• remedy: repeat test after a week

turbidimetry

• measures light blocked

• light detection device is indirect line with the incident light

nephelometry

• measures light scattered

• light detection device is at an angle from the incident light

• more sensitive than turbidimetry

single linear diffusion (oudin)

• antibody is incorporated into agarose in a test tube

• antigen is layered on top, moves down the gel, and precipitation occurs

• precipitation moves down the tube in proportion to antigen concentration

single radial diffusion/radial immunodiffusion

• antibody is uniformly distributed in the support gel

• antigen is placed in a well cut into the gel

• area of the ring obtained is a measure of antigen concentration

mancini/endpoint method

• antigen is allowed to diffuse to completion and when equivalence is reached, there is no further change in diameter

• square of the diameter is proportional to antigen concentration

fahey & mckelvey/kinetic method

• measurements are taken before point of equivalence is reached

• diameter is proportional to the log of antigen concentration

double radial diffusion (ouchterlony)

• both antigen and antibody diffuse independently through a semisolid medium in two dimensions

• antibody is placed in the central cell

• antigens are placed in the surrounding wells to determine of antigens share identical epitopes

• result: precipitin line

rocket immunoelectrophoresis/one-dimension electroimmunodiffusion

• rid + electrophoresis

• antibody is uniformly distributed in the gel

• antigen is placed in wells cut in the gel

• result: precipitin rocket

immunoelectrophoresis

• serum (containing antigens) is electrophoresed

• antibody is placed in a trough

• result: precipitin arc

immunofixation electrophoresis

• serum (containing antigens) is electrophoresed

• antibody is overlaid directly to the gel’s surface

• result: precipitin band

agglutination

• process by which particulate antigens such as cells aggregate to form larger complexes when a specific antibody is present

sensitization

• antigen-antibody combination through single antigenic determinants on the particle surface

lattice formation

• sum of interactions between antibody and multiple antigenic determinants; formation of cross-links that form the visible aggregates