Specific ganglioside binding to receptor sites on T lymphocytes that couple to ganglioside-induced decrease of CD4 expression

The binding of different gangliosides to rat T-helper lymphocytes was characterized under conditions that decrease CD4 expression on different mammalian T-helper lymphocytes. Saturation binding by monosialylated [³H]-GM₁ to rat T-lymphocytes was time- and temperature-dependent, had a dissociation constant (K_D) of 2.2 ± 1.4 μM and a binding capacity near 2 fmoles/cell. Competitive inhibition of [³H]-GM₁ binding demonstrated a structural-activity related to the number of unconstrained sialic acid moieties on GM₁-congeneric gangliosides. A comparison between the results of these binding studies and ganglioside-induced decrease of CD4 expression demonstrated that every aspect of [³H]-GM₁ binding concurs with gangliosides modulation of CD4 expression. It is concluded that the specific decrease of CD4 expression induced by pretreatment with gangliosides involves the initial process of ganglioside binding to specific sites on CD4^-+ T-helper lymphocytes.