Behavior of aldehyde moieties involved in the activation of suppressor cells by sodium periodate

The treatment of mouse spleen cells with periodate at the optimal mitogenic concentration (1 mM) induces the activation of suppressor cells of the in vitro antibody response and leads to the formation of aldehydes on the carbohydrate termini of the surface sialoglycoconjugates. These aldehyde moieties are found on the C8 (N-AN 8) and the C7 (N-AN 7) derivatives of sialic acid. Immediate borohydride reduction prevents the activation of the suppressor cells. Data from this work show that borohydride reduction must be performed within the first 6 hr to prevent the generation of suppressor cells; 18 hr after the initial periodate oxidation, borohydride treatment did not reverse the in vitro suppressive activity of periodate-treated cells. The kinetics of the disappearance of aldehydes from the cell surface were studied by using [3H]borohydride labeling and chromatographic analysis of sialic acid derivatives. About 70 to 80% of the aldehyde moieties were found to be present 6 hr after periodate oxidation. After 18 hr, 50 to 70% of the aldehyde had disappeared from the lymphocyte membrane. Oxidized sialyl residues disappear completely after 60 hr of culture. This period corresponds to the de novo synthesis of sialic acid residues on the surface of periodate-activated cells. The two classes of oxidized sialyl-glycoconjugates were found to behave in different ways. In effect, our data showed that the aldehydes remaining at 18 hr are mainly located on the gangliosides, whereas the aldehyde moieties located on high m.w. glycoproteins disappear from the cell surface between 9 and 18 hr. This would suggest that the remaining aldehydes located on gangliosides are not directly involved in the expression of suppressive activity.