CHARACTERIZATION OF MONOCYTE-ACTIVATING TUMOR-CELL MEMBRANE STRUCTURES

Tumour cells are known to activate monocytes/macrophages and it has be en shown that this stimulation was conferred by tumour-cell membranes. In order to analyse the relevant structures for tumour cell-specific TNF-induction monocytes from healthy donors were cultured in the prese nce of plasma membrane preparations from Jurkat or K562 cells. Both tu mour cell lines revealed a monocyte-stimulating plasma membrane compon ent of about 45 kDa. The TNF-inducing factor exhibited characteristics of a glycoprotein with the carbohydrate moiety as the structure respo nsible for stimulation. CD2, a glycosylated T-cell specific membrane c omponent, was identified as being involved in monocyte activation in t he case of the Jurkat cells whereas the identity of the activating str ucture on K562 cells is still unknown. From the data presented here in dicating the importance of carbohydrate structures for monocyte activa tion we conclude that altered glycosylation of cell surface molecules of tumour cells might be responsible for tumour cell-induced monocyte stimulation.