Evidence for both endogenous and exogenous sources of the sphingomyelin storage in lymphoid cell lines from patients with Niemann-Pick disease types A and B

Epstein-Barr virus-transformed lymphoid cell lines from normal individuals and from patients with Niemann-Pick disease types A, B or C were subjected to various culture conditions in order to study the source of the characteristic lysosomal storage of sphingomyelin observed in the tissues of Niemann-Pick patients. The culture medium was supplemented with a serum substitute devoid of lipoproteins or with one of the following lipid sources: fetal calf serum, human low-density lipoprotein (LDL), or human high-density lipoprotein (HDL). Storage of sphingomyelin was demonstrated under all tested culture conditions in cells deficient in acid sphingomyelinase (Niemann-Pick disease types A and B). In contrast, the sphingomyelin concentration in the lymphoid cell line from a Niemann-Pick type C patient (not deficient in sphingomyelinase) was normal. After more than 30 days in a medium devoid of sphingomyelin, the Niemann-Pick types A and B lymphoid cell lines showed accumulation of sphingomyelin about twice control. The concentration was higher when cells were grown in a medium supplemented with lipids, particularly human LDL or HDL. These results are consistent with the hypothesis that both exogenous and endogenous sphingomyelins participate in the lysosomal storage observed in lymphoid cell lines from patients with Niemann-Pick disease types A and B.