Objectives: Hypericum perforatum L. is a medicinal plant containing many polyphenolic compounds, including flavonoids and phenolic acids with antidepressant and anti-inflammatory properties. This study was investigated the effects of Hypericum perforatum extract (HPE) on immunity, body weight (BW), and spleen index (SI) in rats. Materials and Methods: A total of 24 Wistar male rats were randomly received 4 different doses (6 rats each) of HPE (0, 100, 200 and 400 mg/kg BW) intraperitoneally for 14 days using a completely randomized design. On days 1 and 7, rats were received 0.5 ml SRBC (10%) injection. Blood samples were collected on day 14 to evaluate IgG titer and leukocyte count. On days 1, 7 and 14, the BW and on day 14 spleen were weighted for SI. Results: The IgG titer increased with higher doses of HPE. The HPE increased number of lymphocytes at 200 mg but decreased at 400 mg, number of neutrophils decreased at 200 mg but increased at 400 mg, and number of monocytes increased at 100 mg and 200 mg but decreased at 400 mg (p<0.01). Increasing doses of HPE lowered BW (p<0.01). The HPE increased SI at 100 mg and 200 mg but decreased at 400 mg (p>0.072). Conclusions: The results showed that HPE slightly improved IgG titer but significantly increased the number of leukocytes and monocytes at 200 mg, and neutrophils at 400 mg. The HPE decreased BW at 100 mg and 200 mg with no damage on spleen.

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