Euphorbia hirta L. (Euphorbiaceae) (E. hirta) is a tree locally used as a traditional medicine in Africa and Australia to treat numerous diseases such as hypertension, respiratory ailments, tumors, antipyretic, anti-inflammatory activities. In the present study, we investigated the anti-arthritic activity of fresh leaves of E. hirta ethanol extract that was found to inhibit the production of inflammatory mediators and cytokines of adjuvant arthritis in rats. Adjuvant arthritis was induced in rats (Wistar) by the subplantar injection of 0.05 ml freshly prepared suspension (5.0 mg/ml) of steam killed Mycobacterium tuberculli in liquid paraffin. Animals were treated with graded doses of 25, 50, 100 and 200 mg/kg of E. hirta ethanol extract, p.o. E. hirta significantly inhibited the swelling of the adjuvant-induced arthritis. Moreover, E. hirta at higher dose (200 mg/kg) showed 40.54 ± 1.09 % of CD3+, 15.1 ± 0.76 % of CD4+, 12.2 ± 1.18 % of CD8+ T cell receptor and 17.6 ± 1.11 % gated of CD19+ B cell receptor revealing a down regulation of adjuvant-induced arthritis as compared to the corresponding valves of the arthritic control rats. According to the results shown in Tables 1, 2, the production of IL-1β, TNF-α, IL-2 and IFN-γ were increased in splenocytes of arthritic rats and this increased level was reduced by E. hirta. Also, E. hirta significantly down regulated lipopolysaccharide (LPS)-induced production of nitric oxide production in peritoneal macrophages. These results suggest that E. hirta exhibits an improvement in adjuvant-induced arthritis through down regulation of activated macrophages and T lymphocytes functions. Such unique effects of E. hirta shown on adjuvant arthritis rat model may be advantageous to the long-term treatment of clinical rheumatoid arthritis. Table 1 Effect of E. hirta and prednisolone (Pred) on LPS-induced IL-1β and TNF-α productions from splenocytes in Mycobacterium tuberculli-induced inflammatory arthritic rats Treatment Dose (mg/kg) IL-1β (pg/ml) TNF-α (pg/ml) Arthritic control (AC) - 323.56 ± 31.65 180.91 ± 24.12 E. hirta 25 311.19 ± 29.08* 171.43 ± 22.54* E. hirta 50 287.12 ± 26.98* 164.54 ± 21.76** E. hirta 100 243.12 ± 19.21*** 157.30 ± 18.54*** E. hirta 200 215.21 ± 16.05*** 138.43 ± 17.98*** Prednisolone (Pred) 5 187.18 ± 15.21*** 123.77 ± 15.12*** Normal control (NC) - 54.12 ± 12.54 71.94 ± 12.12 Each value indicates the mean ± SEM of six animals AC arthritic control, NC normal control; E. hirta (25, 50, 100 and 200 mg/kg) and prednisolone (5 mg/kg) were given p.o. from day 0 to day 21 after Mycobacterium tuberculli injection, respectively * p < 0.05; ** p < 0.01; *** p < 0.001, compared to arthritic control Table 2 Effect of E. hirta and Prednisolone (Pred) on Con A-induced IL-2 and IFN-γ productions from splenocytes in Mycobacterium tuberculli-induced inflammatory arthritic rats Treatment Dose (mg/kg) IL-2 (pg/ml) IFN-γ (pg/ml) Arthritic control (AC) - 235.98 ± 15.23 165.95 ± 13.87 E. hirta 25 225.12 ± 14.76** 154.76 ± 11.07** E. hirta 50 207.76 ± 13.87** 134.76 ± 11.01** E. hirta 100 189.98 ± 12.65 *** 110.64 ± 10.98*** E. hirta 200 157.84 ± 14.32 *** 98.54 ± 10.76*** Prednisolone (Pred) 5 131.08 ± 13.31*** 87.65 ± 10.61*** Normal control (NC) - 78.12 ± 12.04 31.87 ± 10.12 Each value indicates the mean ± SEM of six animals AC arthritic control, NC normal control; E. hirta (25, 50, 100 and 200 mg/kg) and prednisolone (5 mg/kg) were given p.o. from day 0 to day 21 after Mycobacterium tuberculli injection, respectively * p < 0.05; ** p < 0.01; *** p < 0.001, compared to arthritic control.