Autologous lymphocyte-monocyte co-culture increases NMR-visible and cytoplasmic lipids in the absence of increased markers of lymphocyte activation

Alterations in nuclear magnetic resonance (NMR)-visible lipid, morphometric lipid volume fraction, distribution of subcellular lipid droplets and acti vation antigen expression were examined in human peripheral blood lymphocyt es, activated using phorbol myristate acetate (PMA) and ionomycin or by co- culture with autologous monocytes. PMA/Ionomycin treatment caused significa nt time-dependent increases in mobile lipid and in oil red O-positive lipid droplets that were accompanied by lymphocyte proliferation and increases i n activation antigens, CD25, CD69 and CD71. Co-culture of lymphocytes and m onocytes also induced significant increases in NMR-visible lipid signals an d cytoplasmic lipid droplets, but in contrast, no correspondent increases i n activation antigens were observed. Strong correlations were observed betw een the intensity of the NMR signal and the percentage of total cells conta ining lipid droplets (r = 0.95) and the morphometric lymphocyte lipid volum e fraction (r = 0.80), indicating that the droplets were the source of the mobile lipid signal. Lipid droplets in PMA/Ionomycin-treated cells were eve nly distributed throughout the population, but in co-cultures, only lymphoc ytes in close proximity to monocytes with lipid droplets contained oil red O-positive lipid. This data shows that the NMR-visible mobile lipid signal observed in lymphocytes co-cultured with monocytes is not directly dependen t on either proliferation or the upregulation of activation antigens, simil ar to the previously observed response of T cells exposed to antibodies to the T cell receptor. (C) 2001 Elsevier Science B.V. All rights reserved.