The relationship between sialic acid content and peanut agglutinin binding on senescent and enzyme treated human erythrocytes

Young, old and neuraminidase treated human red blood cells (RBC) were investigated with peanut agglutinin (PNA), a lectin with a specificity similar to that of serum T-agglutinin. The effect of serum agglutinins on this interaction was also investigated. The density and distribution of PNA receptors were evaluated by agglutination with PNA and binding of ferritin-conjugated PNA (PNA-F), or PNA labeled with radioactive iodine ([¹³¹I]PNA). The results were correlated with the distribution of membrane bound sialic acids, as evaluated by chemical analysis and rate of agglutination with poly-l-lysine (PLL). Untreated RBC of all ages did not agglutinate with PNA and failed to bind PNA-F and [¹³¹I]PNA. Treatment of young RBC with neuraminidase, which resulted in reduction of membrane-bound sialic acids to an extent similar to that of physiologically aged RBC, resulted in the concomitant exposure of PNA binding sites and in the agglutination of these cells by autologous serum. Pretreatment of the neuraminidase treated RBC with autologous serum resulted in partial inhibition of the binding capacity of PNA on the RBC. The results indicate that the normal age-related loss of sialic acids in circulating RBC is not identical with enzymatic removal of sialic acids by neuraminidase. The observations suggest that different mechanisms are functional in the recognition and sequestration of old RBC and of RBC treated with neuraminidase.