Expression of 5‐lipoxygenase (5‐LOX) in T lymphocytes

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Abstract
Summary: 5‐lipoxygenase (5‐LOX) is the key enzyme responsible for the synthesis of the biologically active leukotrienes. Its presence has been reported in cells of the myeloid lineage and B lymphocytes but has not been formally defined in T lymphocytes. In this study, we provide evidence for 5‐LOX expression on both transcriptional and translational levels in highly purified peripheral blood T cells as well as in human T lymphoblastoid cell lines (MOLT4 and Jurkat). Messenger RNA (mRNA) of 5‐LOX was amplified by conventional reverse transcription–polymerase chain reaction (RT‐PCR; MOLT4 and Jurkat cells) and by in situ RT‐PCR (T lymphocytes). 5‐LOX protein expression was confirmed by Western blot and immunofluorescence studies. 5‐LOX was present primarily in the cytoplasm with some nuclear localization and was translocated to the nuclear periphery after culture in a mitosis‐supporting medium. Fluorescence‐activated cell sorter analysis of different T‐lymphocyte populations, including CD4, CD8, CD45RO, CD45RA, T helper type 2, and T‐cell receptor‐αβ and ‐γδ expressing cells, did not identify a differential distribution of the enzyme. Purified peripheral blood T lymphocytes were incapable of synthesizing leukotrienes in the absence of exogenous arachidonic acid. Jurkat cells produced leukotriene C4 and a small amount of leukotriene B4 in response to CD3–CD28 cross‐linking. This synthesis was abolished by two inhibitors of leukotriene synthesis, MK‐886 and AA‐861. The presence of 5‐LOX in T lymphocytes but the absence of endogenous lipoxygenase metabolite production compared to Jurkat cells may constitute a fundamental difference between resting peripheral lymphocytes and leukaemic cells.

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