Truong Quynh Nhu^a,b*, Bui Thi Bich Hang, Mélodie Schmitz , Anaïs Vinikas, Nguyen Phuong Trang , Joëlle Quetin-Leclerc,  Bui Thi Buu Hue, Le Thi Bach, Nguyen Le Anh Dao , Tran Minh Phu, Do Thi Thanh Huong,  Marie-Louise Scippo, Nguyen Thanh Phuong , Patrick Kestemont
^aResearch Unit in Environmental and Evolutionary Biology, University of Namur, Belgium
^bCollege of Aquaculture & Fisheries, Can Tho University, Can Tho, Vietnam
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Regular use of antibiotics and other chemotherapeutics in controlling diseases has caused and is still causing many negative impacts for the environment and food safety. Therefore, there is an increased demand to look for eco-friendly preventive measures to promote sustainable aquaculture, as for example antibiotic alternatives. Here, we developed an in vitro leukocyte assay for screening immune responses (lysozyme, complement and total immunoglobulin activities) and applied it on 20 herbal extracts from plants collected in Vietnam, in the aim to select plant extracts with immunostimulating properties. Peripheral blood mononuclear cells (PBMCs) and kidney cells (5x10⁶ cells/ml) obtained from striped catfish (Pangasisanodon hypophthalmus) were cultured for 24h in L-15 medium supplemented with 1% dimethyl sulfoxide (DMSO- serve as negative control) and two different levels (10 and 100 µg/ml) of herbal extracts. Results indicated that 12 out of the 20 extracts were identified to have a strong effect on specific and non-specific immune responses of striped catfish leukocytes. Levels of innate immune responses differed between extracts and concentrations as compared to the control. The highest stimulations of complement and lysozyme activities as well as total Ig in blood and kidney of striped catfish were found after exposure to 10 µg/mL of Zingiber officinale Rosc., Phyllanthus urinaria L., Allium sativum L. Others were only effective at 100 µg/mL  (Euphorbia hirta L., Azadirachta indica A. Juss). On the other hand, some other plant extracts (Mimosa pudica L., Ageratum conyzoides L., Eclipta prostrata (L.) L.) induced a depression of the immune response, when compared to control. Results from this in vitro screening study are useful to select the best herbal extracts for future in vivo experiments.

Key words: Immune response, Pangasianodon hypophthalmus, herbal extracts, PBMCs.