Lipoproteins induce tyrosine phosphorylation in human natural killer cells

Lipoproteins, chylomicrons (Ch?), very low density lipoprotein (VLDL), low density lipoprotein (LDL), high density lipoprotein (HDL) and acetyl modifi ed LDL (AcLDL) can stimulate natural killer (NK) cells upon binding to spec ific receptors. Using flow cytometry and a specific monoclonal antibody aga inst phosphotyrosine, we assessed the effect of lipoproteins on total intra cellular expression of immunoreactive phosphotyrosine. Tyrosine phosphoryla tion increased when lipoproteins were added to purified NK cells, previousl y cultured overnight in RMPI-0.5% fatty acid free bovine serum albumin. The optimal effect occurred at 15 minutes for all the lipoproteins used. The c oncentrations of lipoprotein were 10 mu g of protein/ml of CM, and 20 mu g of protein/ml for the other lipoproteins. The effect of lipoproteins on pho sphotyrosine positivity was as follows: LDL > VLDL > CM > HDL > AcLDL. Thus lipoproteins may activate NK cells through tyrosine phosphorylation and th is signal transduction pathway seems to be enhanced when these cells are ac tivated with LDL. Med Sci Res 26:795-797. (C) 1998 Lippincott Williams & Wi lkins.