Erythrocyte binding properties of streptococcal lipoteichoic acids

The lipoteichoic acids (LTA) of gram-positive bacteria are known to bind spontaneously to a variety of animal cell membranes. The authors investigated the biological and biochemical characteristics of the binding of LTA of Streptococcus pyogenes and S. faecalis to human and sheep erythrocytes. The kinetics of the binding of the radiolabeled LTA ([³H]LTA) from each of these organisms to erythrocytes was similar. The dissociation constants for sheep and adult human erythrocytes were 1.6 μM and 4.5μM, respectively, whereas that of human cord blood erythrocytes was approximately 10-fold higher, 31 μM. The number of binding sites for sheep erythrocytes was calculated to be 7.2 x x10⁶ per cell, and that of human erythrocytes, 29 x 10⁶ per cell. Binding was reversible. More than 50% of bound [³H]LTA was displaced from erythrocytes by a 50-fold excess of unlabeled LTA. LTA prepared from heterologous species of gram-positive bacteria were all inhibitory to the binding of [³H]LTA whether derived from S. pyogenes or from S. faecalis. Among a number of potential receptor analogues and other inhibitors tested, including serum albumin, gangliosides Gm₂ and Gm₃, lipopolysaccharide of gram-negative bacteria, and various sugars, only albumin and the gangliosides significantly inhibited LTA binding. Trypsin or neuraminidase treatment of erythrocytes had no effect on LTA binding. Deacylation of [³H]LTA abolished binding ability and binding was restored by esterification of the deacylated material with stearoyl chloride, indicating that ester-linked lipids are necessary for membrane binding.