Untitled - D Ank Unlimited

precipitating antibody 588 precipitation curve
is homologous to a V domain. Association of the pre-B
cell receptor with the Igα and the Igβ signal-transduction
proteins forms the pre-B cell receptor complex. Stimulation
of proliferation and continued maturation of developing B
cells requires pre-B cell receptors.
precipitating antibody
A precipitin.
precipitation
Following the union of soluble macromolecular antigen with
a homologous antibody in the presence of electrolytes in
vitro and in vivo that occurs within seconds after contact,
complexes of increasing density form in a lattice arrangement
and settle out of solution, as in the precipitation or precipitin
reaction. The materials needed for a precipitin reaction
include antigen, antibody, and electrolyte. The reaction of
soluble antigen and antibody in the precipitin test may be
observed in liquid or gel media. The reaction in liquid media
may be qualitative or quantitative. Following discovery of the
precipitin reaction by Kraus, quantitative and semiquantitative
measurements of antibody could be made. The term precipitinogen
is sometimes employed to designate the antigen,
and precipitin is the antibody in a precipitation reaction.
Precipitate Formed
Excess
antibody
Equivalence
Antigen Used
Precipitation curve.
Excess
antigen
Precipitation curve.
precipitation curve
The milligrams of antibody in a precipitate are plotted on the
ordinate and the milligrams of antigen added are plotted on
the abscissa of a graph. The precipitin curve contains ascending
and descending limbs and zones of antibody excess,
equivalence, and antigen excess. By testing with homologous
reagents, unreacted antibodies and antigens can be detected
in the supernatants. If antigen is homogeneous or if
antibodies specific for only one of a mixture of antigens are
studied by the precipitin reaction, none of the supernatants
contains both unreacted antibodies and unreacted antigens
that can be detected. The ascending limb of the precipitin
curve represents the zone of antibody excess, where free antibody
molecules are present in the supernatants. The descending
limb represents the zone of antigen excess, where free
antigen is present in the supernatants. Precipitation is maximum
in the zone of equivalence (equivalence point)—neither
antigen nor antibody can be detected in the supernatants. In
contrast to the nonspecific system described above, the presence
of more than one antigen–antibody system in a reaction
medium may be revealed by a demonstration of unreacted
antibody and antigen in certain supernatants. This occurs in
cases of overlap between the zone of antigen excess in one
antigen–antibody combination with the zone of antibody
excess of a separate antigen–antibody system. The lattice
theory proposed by Marrack explains how multivalent antigen
molecules and bivalent antibodies can combine to yield
antigen-to-antibody ratios that differ from one precipitate to
another, depending upon the zone of the precipitin reaction in
which they are formed. When the ratio of antibody to antigen
is above 1.0, a visible precipitate forms; however, when the
ratio is less than 1.0, soluble complexes result and remain in
the supernatant. The soluble complexes are associated with
the descending limb of the precipitin curve. Also termed
precipitin curve.