Action of sphingomyelinase C and other lipid-specific agents as inhibitors of Fc binding and locomotion in human leucocytes.

The binding of antibody-coated chicken erythrocytes (EA) to human blood lymphocytes and monocytes is inhibited by pretreatment of the leucocytes with sphingomyelinase C. Inhibition of rosetting of neuraminidase-treated EA with neutrophils is also seen with this enzyme. The cholesterol-binding theta-toxin of Clostridium perfringens and pronase also inhibit EA-rosette formation, but less strongly than sphingomyelinase. The lipid-specific agents also inhibit chemotactic migration of leucocytes to casein and denatured HSA, whereas proteases and glycosidases do not. These results suggest that membrane lipids are important constituents of the binding sites for Fc fragments and for certain chemotactic factors and point to an important role for sphingomyelin in this binding.