Anti-allergic effects of the ethanol extract of Syzygium formosum (Wall.) Masam leaves and its immunoregulatory mechanisms.

BACKGROUND

As documented in a Vietnamese traditional medical encyclopedia, Syzygium formosum (Wall.) Masam leaves have been routinely used among indigenous Vietnamese people for treatment of various allergy-like symptoms including dermatitis and rhinitis.

OBJECTIVE

Anti-allergic activity of S. formosum leaves was examined with a mouse model of chicken ovalbumin (cOVA)-induced food allergy, and mechanisms underlying the anti-allergic effect were explored.

METHODS

BALB/c mice were administered i.p. cOVA (20μg) plus alum (2mg) twice on day 0 and 14 for sensitization (immunization). Two weeks after the second immunization, the mice were administered cOVA (50mg) p.o. 5 times every 3 days to induce food allergy symptoms (i.e., anaphylaxis, diarrhea, and drop in the body temperature). Ethanol extract of dried leaves of S. formosum (80mg/kg or 200mg/kg body weight) was administered p.o. daily during the induction (challenge) period.

RESULTS

Treatment with the S. formosum leaves ethanol extract ameliorated the allergic symptoms to a significant extent and in a dose-dependent manner. The treatment also resulted in a significant improvement in the inflammatory lesion in the small intestine and reduction in the numbers of mast cells and eosinophils recruited to the lesion. The treatment also brought about a significant reduction in the levels of Th2 cytokines produced by the mesenteric lymph node cells cultured ex vivo with cOVA. The passive anaphylaxis experiment also showed that the extract treatment impaired the mast cell function.

CONCLUSIONS

Our study provides a scientific basis for the traditional (indigenous) use of the S. formosum leaves extract for the treatment of various allergy symptoms in Vietnam. In addition, the results show that the extract has activities to suppress antigen-specific Th2 T cell immune responses and the mast cell function, which are directly related with its anti-allergic effect.