Immunobiological features of the galactoside lectin L-Lc isolated from the Argentine mistletoe Ligaria cuneifolia

Abstract

Ligaria cuneifolia has been used in Argentine folk medicine and is currently employed as substitute for the European mistletoe ( Viscum album) as hypotensor agent. Extracts from V. album are widely used in cancer therapy and the antineoplasic effect is attributed to their cytostatic/cytotoxic and immunomodulatory actions. When studying immunomodulatory effects of L. cuneifolia extracts ( Lc extracts), they inhibited proliferation of murine mitogen-activated lymphocytes, leukaemic lymphocytes (LB) and breast tumour cells (MMT). The aim of this work was to isolate and identify lectins from Lc extracts and investigate their immunobiological actions. A galactoside lectin (L-Lc) of 57 kDa was isolated. A polyclonal antiserum obtained against Lc extract recognised both L-Lc and MLI ( V. album lectin), suggesting the possibility of shared epitopes. Treatment of LB tumour cells with L-Lc (0.01 and 0.1 μg/ml) produced up to 40.0±6.9% inhibition of cell growth, which seems partly mediated by apoptosis (apoptosis of L-Lc treated cells 58.4±10.3% versus non-treated cells 38.1±8.8%; P<0.05), analysed by acridine orange and ethidium bromide staining. Inhibitory effect on ConA stimulated splenocyte growth was non-significant, while a mitogenic effect was observed on normal murine splenocytes and MMT cells. L-Lc in non-cytotoxic concentrations (250 ng/ml) modified mRNA expression of IL-10 but neither that of TGF-β nor of IL-2 produced by LB cells. In addition, 43.9±0.5% reduction in NO production by LPS-stimulated murine macrophages was found. Finally, survival rates of LB tumour-bearing mice treated or not with Lc extract or L-Lc failed to show significant differences.