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Immunomodulatory activity of methanol leaf extracts of Cameroonian medicinal plants

Abstract Background: Medicinal plants have been used for centuries and have become part of complementary medicine worldwide because of their health benefits. Some have been successfully used directly in the treatment and prevention of infectious diseases or indirectly by stimulating the immune system. In the present study, the immunomodulatory activity of the methanol extracts of Adenocarpus mannii, Caucalis melanantha, Ocimum gratissimum, Asystasia intrusa and Clematis chinensis leaves was investigated. Methods: The extracts were prepared by maceration of dry leaves’ powder in methanol. Phytochemical analysis was carried out by chemical reaction methods. The activity of plant extracts was evaluated in in vitro cell cultures by measuring their effect on nitric oxide production by peritoneal macrophages, the proliferation of lymphocytes and the cytotoxic effect on macrophages. The A. mannii extract was further evaluated at 50 and 100 mg/kg body weight in mice for the stimulation of delayed-type hypersensitivity (DTH) reactions and the ability to reverse the myelosuppression induced by cyclophosphamide. Results: All the extract inhibited nitric oxide production by peritoneal macrophages, the highest activity was achieved with C. chinensis extract. However, these extracts did not significantly affect the viability of macrophages. A. mannii, A. intrusa and C. chinensis extracts exhibited stimulatory activity on peripheral blood lymphocytes, whereas C. melanantha and O. gratissimum extracts displayed inhibitory activity. In vivo, the A. mannii extract significantly increased the DTH reaction in mice from 50 mg/kg. This extract also showed a significant increase in the white blood cells and relative weight of the spleen and liver. Conclusions: These results suggest that the A. mannii, C. melanantha, O. gratissimum, A. intrusa and C. chinensis methanol extracts possess immunomodulatory activity. This constitutes additional data on the well-known biological properties of these plants.