Plant lectins displaying similar single
sugar-binding specificity and identical molecular structure might present various
biological effects. To explore this possibility, the effects on human lymphocytes of two
mannose-specific and structurally closely related
lectins,
Morniga M from Morus nigra and
artocarpin from Artocarpus integrifolia were investigated. In silico analysis revealed that
Morniga M presents a more largely open
carbohydrate-binding cavity than
artocarpin, probably allowing interactions with a broader spectrum of
carbohydrate moieties. In vitro,
Morniga M interacted strongly with the lymphocyte surface and was uptaken quickly by cells.
Morniga M and
artocarpin triggered the proliferation and activation of human T and NK lymphocytes. A minority of B lymphocytes was activated in
artocarpin-treated culture, whereas
Morniga M favored the emergence of CD4+ CD8+ T lymphocytes. Moreover, cell death occurred in activated PBMC, activated T lymphocytes, and Jurkat T
leukemia cells incubated with
Morniga M only. The
biological effects of both
lectins were dependent on
carbohydrate recognition. The
Morniga M-induced cell death resulted, at least in part, from caspase-dependent apoptosis and FADD-dependent receptor-mediated cell death. Finally,
Morniga M, but not
artocarpin, triggered AICD of T lymphocytes. In conclusion, both
lectins trigger lymphocyte activation, but only
Morniga M induces cell death. In spite of similar in vitro
mannose-binding specificities and virtually identical structure, only
Morniga M probably interacts with
carbohydrate moieties bound to molecules able to induce cell death. The present data suggest that subtle alterations in N-
glycans can distinguish activation and cell death molecules at the lymphocyte surface.