Anti-D prozone and membrane sulfhydryl modification.
An IgG anti-D prozone is produced by progressive inactivation of the D antigen following red cell exposure to increasing concentrations of thimerosal and phenol present as antibody excess is achieved. Partial inactivation of the D antigen by routinely added thimerosal, an organic mercurial, and phenol is associated with an unstable D antigen-antibody complex resulting in an increased rate of dissociation of anti-D and with a decreased reactivity of the cell-bound anti-D in the antiglobulin reaction. Complete D inactivation occurs with concentrations in excess of 0.43 microM thimerosal. If attributable to inactivation of a surface-exposed sulfhydryl group, it suggests that less than 5 percent of these are involved in D-antigen activity. The data do not exclude the possibility that D inactivation may result from alteration of sulfhydryl groups other than those exposed at the surface.