Neutral glycosphingolipids induce cell-cell aggregation of a variety of hematopoietic cell lines

Exogenous neutral glycosphingolipids induced homotypic cell-cell aggregation of a variety of hematopoietic cell lines. A mouse cytotoxic T cell line, CTLL-2, was chosen to study the neutral glycosphingolipid-induced aggregation. Among neutral glycosphingolipids tested, galactosylceramide (GalCer) and glucosylceramide (GlcCer) were potent inducers, followed by lactosylceramide (LacCer); globotriaosylceramide (Gb3Cer) and neolactotetraosylceramide (nLc4Cer) were less effective. GalCer that contained a non-hydroxy fatty acid was more efficient than GalCer containing an alpha-hydroxy fatty acid. The minimum concentration of GalCer containing a non-hydroxy fatty acid that induced aggregation was 1 microM, and maximum aggregation occurred at 10-20 microM within 24 h. Cytochalasin B and a mixture of sodium azide and 2-deoxyglucose inhibited the aggregation, whereas cycloheximide, actinomycin D, and colchicine did not. Aggregated and dispersed cells, which were designated as competent cells, re-aggregated in the absence of neutral glycosphingolipids. Anti-GalCer polyclonal antibody inhibited GalCer-induced reaggregation. Furthermore, competent cells bound and aggregated non-competent cells in the absence of neutral glycosphingolipids. Cell-cell aggregatign was similar for CTLL-2 cells and the other hematopoietic cells that were tested. These findings suggest that the neutral glycosphingolipid-induced cell-cell aggregation of CTLL-2 cells was mediated by heterophilic interaction(s) between glycosphingolipids and other cell surface components. These properties are shared by a variety of hematopoietic cell lines.