Volvariella volvacea lectin activates mouse T lymphocytes by a calcium dependent pathway

The immunomodulatory lectin, Volvariella volvacea lectin (VVL), isolated from the edible mushroom, Volvariella volvacea, has been shown to stimulate the expression of Th1 cytokines and the proliferative activity of mouse splenocytes (She et al. [1998]: Biochem Biophys Res Comm 247:106–111). In order to elucidate the mechanisms underlying these activities, we conducted a kinetic analysis of the early and late activation markers in mouse T lymphocytes: (1) flow cytometric analysis of calcium influx, (2) induction of activation molecules (CD25 and CD69), (3) expression and DNA-binding activity of the nuclear factor of activated T cells (NFAT), NFκB, and activation protein-1 (AP-1), (4) translational production of cytokines (interleukin-2 (IL-2) and interferon-γ (IFNγ)), and (5) cell proliferation by expression of proliferating cell nuclear antigen (PCNA) and tritiated thymidine incorporation. All results showed that VVL induced a rapid expression of CD69, CD25, NFAT, IL-2, and PCNA in a dose- and time-dependent manner, leading to lymphocyte proliferation. These effects brought about by VVL were more potent than those stimulated by equimolar concentrations of mitogenic lectin, concanavalin A (Con A). Cell activation and proliferation were mediated through a calcium-dependent pathway as demonstrated by a VVL-induced increase of intracellular calcium influx, and a proliferation inhibition by the Ca-dependent phosphatase calcineurin blocker—cyclosporin A (CsA). Taken all data together, VVL is a lectin which activates lymphocyte through successive calcium influx, nuclear localization of NFAT transcription factor, induction of activation markers, CD25 and CD69, intracellular cytokine production, and cell proliferation.