A NEW SURFACE MARKER ON EQUINE PERIPHERAL-BLOOD LYMPHOCYTES .1. SUBPOPULATIONS OF LYMPHOCYTES WITH RECEPTORS FOR HELIX-POMATIA A HEMAGGLUTININ (HP)

Untreated and neuraminidase-treated equine peripheral blood lymphocytes were analyzed for binding of the A hemagglutinin of the snail H. pomatia (HP). For optimal staining by direct immunofluorescence, the concentration of neuraminidase had to be increased as compared to that needed for other species. Higher concentrations of HP were required for optimal staining of equine lymphocytes as compared to lymphocytes from other species. Even so, the maximal number of equine lymphocytes exhibiting positive staining was only .apprx. 20%. No, or very few, HP-positive lymphocytes were seen when neuraminidase treatment was omitted. When the more sensitive method of indirect immunofluorescence was used, .apprx. 60% of the lymphocytes were HP positive without prior treatment with this enzyme. Neuraminidase treatment significantly increased this figure to .apprx. 75%. In all instances, HP binding was specific since it was inhibited by the competitive sugar hapten N-acetyl-D-galactosamine (D-GalNAc) while addition of D-glucose (D-Glc) gave no inhibition. HP binding to neuraminidase-treated lymphocytes was also investigated quantitatively by means of 125I-labeled HP. The number of HP molecules bound per HP-positive cell was .apprx. 3 .times. 105 and the apparent association constant for the binding of HP to its cellular receptors was .apprx. 8 .times. 107 l/mol. No binding of HP to untreated lymphocytes could be recorded in these experiments.