[Frontiers in Bioscience, Elite, 5, 558-573, January 1, 2013] 558 T-cell activation induces selective changes of cellular lipidome Tapio Lonnberg 1 , Laxman Yetukuri 2 , Tuulikki Seppanen-Laakso 2 , Riitta Lahesmaa 1 , Matej Oresic 2 1 Turku Centre for Biotechnology, University of Turku and Abo Akademi University, Turku, Finland, 2 VTT Technical Research Centre of Finland, Espoo, Finland TABLE OF CONTENTS 1. Abstract 2. Introduction 3. Material and methods 3.1. CD4 + cell isolation 3.2. Cell stimulation and culture 3.3. Harvesting 3.4. Lipidomic analysis 3.5. Clustering analysis 4. Results 4.1. Lipid composition of naïve T helper precursor cells 4.2. Alterations of lipid concentrations in response to T-cell activation 4.3. Changes in PC and PE fatty acid change lengths and degree of saturation during development of activated T-cell phenotypes 4.4. Transcriptional regulation of lipid metabolism 5. Discussion 6. Acknowledgements 7. References 1. ABSTRACT Activation of naïve T helper cells by presentation of cognate antigen initiates a complex intracellular signaling process leading to development of functionally active effector cell population. The switch from quiescent naïve state to activated state involves a profound change of cellular metabolism, required for completion of multiple rounds of proliferation. Using ultra performance liquid chromatography mass spectrometry, we analyzed how this change is reflected on the cellular lipid composition in human umbilical cord blood T-cells. We found that considerable concentration changes take place during the first 72 hours after T-cell receptor activation, correlating with first rounds of activation-induced cell division. Most importantly, composition of phosphatidylcholines and phosphatidylethanolamines exhibited consistent trend towards shorter and more saturated molecular species. Together with related transcriptomics data, the results clearly suggested induction of de novo fatty acid synthesis and accumulation of endogenously synthesized fatty acids into the cellular membranes, leading to partial remodeling of the cellular lipidome in the newly developed effector cell population. 2. INTRODUCTION T helper cells constitute the topmost regulatory layer of the adaptive immune system, controlling the activity of all downstream immune cell types and thus coordinating all acquired immune responses. The activity of T helper cells themselves is determined by T-cell receptor-mediated activation by cognate peptide-MHC complexes and subsequent cytokine-influenced differentiation of functionally distinct effector subsets, namely Th1, Th2, and Th17 cells(1-3). These processes are prerequisites for the specificity and memory that are the hallmark features of acquired immune responses. Since the fundamental function of T-cell activation is to recognize pathogenic non-self peptides in an environment dominated by innocuous and self molecules, extremely tight and specific regulation is required. Importantly, contrary to the functions of many other cell surface receptors, T-cell activation does not follow typical mass action kinetics where rate of the reaction is determined by concentrations of participating molecules. Instead, remarkably complex network of intracellular