35: Sterile inflammation: Surface LIPIDS on STIMULATED T cells that induce cytokine production in human monocytes/macrophages

Abstract

Imbalance in cytokine homeostasis plays an important part in the pathogenesis of chronic/sterile inflammatory diseases such as multiple sclerosis and rheumatoid arthritis. Stimulated T cells exert a pathological effect through direct cellular contact with monocytes/macrophages, inducing a massive up-regulation of IL-1β and TNF in the latter cells. This mechanism that is likely to be relevant to chronic/sterile inflammation is specifically inhibited by high-density lipoproteins (HDL). Here we determine that cytokine induction is due to lipids present in membranes of stimulated T cells. Total lipids from plasma membrane were extracted from HUT-78 cells and peripheral blood T lymphocytes stimulated and unstimulated by PHA/PMA. Lipids extracted from stimulated HUT-78 and stimulated blood T lymphocytes induced IL-1β, sIL-1Ra and TNF production in monocytes, whereas lipids from unstimulated cells did not. Pro-inflammatory cytokine production was inhibited in the presence of HDL. These results indicated that lipids were the active factors that induced cytokine production upon direct cellular contact activation of monocytes. The activity was abolished when lipids were treated with methylamine suggesting that sphingolipids were not involved in monocyte activation. Preliminary identification of surface lipids implicated in the induction of cytokine production in monocytes was performed. Surface lipids of stimulated and unstimulated HUT-78 cells were separated in a Synergy 4 μm MAX-RP 18A column and mass spectrometry analysis of active fractions was carried out. Results suggest the involvement of T cell lysophospholipids and phosphatidic acids in the induction of cytokine production in human monocytes. Our results demonstrate that stimulated T cells display bioactive lipids at their surface which induce cytokine production in human monocytes. The identification of these lipids might open the way to new therapeutic approaches in chronic/sterile inflammatory disorders such as rheumatoid arthritis and multiple sclerosis.