(276c) Dependence of Membrane Antigen Expression On Cross-Over Frequency of Human Erythrocytes and Corresponding Theoretical Explanation

Since Pohl's initial exploration of dielectrophoretic force
to explain the behavior of polarizable particles in a non-uniform electric
field, adjustments have been made to the Clausius-Mossotti factor to include
non-spherical particles and particles of a core-shell composition.  This work has become increasingly
important since dielectrophoresis has been applied to biological cell systems
because it allows for the separation and sorting of cells of similar origin but
slightly varying dielectric properties. 
Knowing the frequency at which the Clausius-Mossotti factor is equal to
zero allows the researcher to determine the conductivity and permittivity of
the cell of interest.  However,
current equations describing the Clausius-Mossotti factor ignore slight
membrane differences such as antigen expression despite previous results
showing that small membrane changes make appreciable changes to the
Clausius-Mossotti factor.  This
work builds upon the previous adjustments made to the dielectrophoretic force
equation to account for not only the shelled ellipsoidal shape of human
erythrocytes but also the differences in membrane antigen expression.  The common ABO-Rh typing system
consists of 4 different membrane antigens and provides the basis for these
studies.  The Rhesus factor (Rh) is
a group of transmembrane antigens that indicate positive blood type (presence
of D antigen) or negative blood type (absence of D antigen).  The ABO blood grouping system consists
of three surface antigens, whose presence or absence dictate blood type.  A and B antigen chains differ from the
O backbone by a single sugar molecule, however this small difference gets
magnified because there are 1.5 million copies of the antigen on the
erythrocyte surface.  In order to
determine the affect of the ABO antigens on the dielectrophoretic behavior,
erythrocytes were treated with β(1-3) galactosidase,
which cleaves polysaccharide antigens at a galactose bond.  Human erythrocytes of known ABO-Rh
blood type were suspended in a 0.1S/m dextrose buffer solution and subjected to
an electric field of 0.1V/μm and varying frequency from 100kHz
to 80MHz in order to determine their cross-over frequencies.  Experiments were repeated with β(1-3) galactosidase treated erythrocytes. It was
found that the lower cross-over frequency is ABO blood
type dependent and that galactosidase modification causes a shift in the
cross-over frequency.  The higher
cross-over frequency was Rh blood type dependent and did not change after β(1-3) galactosidase modification.  The change in the lower cross-over frequency post-modification proved that the
polysaccharide antigen chain influences the dielectric properties of the
erythrocyte and therefore the dielectrophoretic behavior.  The shelled ellipsoidal
Clausius-Mossotti factor model was fit to each ABO blood type response to
quantify membrane conductivity differences due to antigen expression.  This work will provide insight into
molecular level contributions to conductivity and permittivity –driven
cell polarizations in dielectrophoretic fields.