J. Lee et al., DEMONSTRATION OF IGM ANTIBODIES OF HIGH-AFFINITY WITHIN THE ANTI-GAL-ALPHA-1-3GAL ANTIBODY REPERTOIRE, Transplantation, 66(8), 1998, pp. 1117-1119
Background. Human anti-Gal alpha 1-3Gal IgG and IgM xenoantibodies can
distinguish between very similar epitopes with a high degree of selec
tivity. Methods. Anti-Gal alpha 1-3Gal antibodies were affinity isolat
ed using two separate Gal alpha 1-3Gal-based immunoadsorbents, Gal alp
ha 1-3Gal itself and Gal alpha 1-3Gal beta 1-4Glc. IgG and IgM were se
parated using a protein G column. Antibody purity was achieved by seri
al adsorption/elutions from the columns. By this means, different anti
body fractions were prepared that contained either IgG or IgM, reactiv
e with either Gal alpha 1-3Gal, Gal alpha 1-3Gal beta 1-4Glc, or both.
The dissociation equilibrium constants (K-d) of these antibodies were
then measured using an IAsys biosensor. Results and Conclusions. Sera
from two individuals were used and K-d values for one IgG (fraction 1
A) and two IgM (fractions 1B and 2A) fractions were obtained. The K-d
for the IgG was 4.85 x 10(-7) M (fraction 1A). Far IgM, the K-d values
were higher at 7.8x10(-10) M (fraction 1B) and 1.07x10(-10) M (fracti
on 2A). Natural anti-pig antibodies include high affinity IgM that con
tinue to be produced without class switch. The B cell mechanism behind
this is not known. It may be possible to exploit this mechanism in fu
ture xenotransplantation strategies.