Passive modulation of blood-group antigens.

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Abstract
Rh-positive human erythrocytes were enriched and depleted of membrane cholesterol, and the mediated change in the degree of exposure of the D antigens was determined by fluorescence-activated cell sorting, using indirect fluorescent antibody labeling. The results were compatible with a model in which the expression of the D antigens could be modulated significantly by the lipid microviscosity (.hivin..eta.). At a high cholesterol-to-phospholipid ratio (C/PL) of 1.55, which corresponds to .hivin..eta. (25.degree. C) = 7.5 poise (1 poise = 0.1 Pa[Pascal].cntdot.), the relative detectable number of D antigens was about double than that at C/PL = 0.65, .hivin..eta. (25.degree. C) = 4.1 poise. In analogous experiments similar fluidity changes resulted in only about 20% modulation of expression of the A1 antigen, suggesting that in the native state this antigen is already well-exposed on the erythrocyte surface. This type of antigenic modulation may also operate in vivo, and may thus bear some fundamental implications on tumor immunology and autoimmune diseases.
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