Objective: To investigate the therapeutic effect of sodium paeonolsilate on experimental immunologic conjunctivitis in mice and to explore the mechanism of action. Methods: This was an experimental study.The Balb/c mice which immunologic conjunctivitis was initiated by intraperitoneal injection with ovalbumin (OVA) were randomly assigned to five treatment groups (Groups B-F, n=6 mice each), and another 6 mice served as uninjected controls (Group A). Both eyes of each mouse were treated with eyedrops 7 days after as follows: Group A, uninjected controls treated with phosphate-buffered saline (PBS); Group B, model group treated with PBS; Group C, treated with 1% sodium paeonolsilate group;Group D, treated with 2% sodium paeonolsilate group; Group E, treated with sodium cromoglicate;Group F, treated with olopatadine. After five days of medication or control treatments, ocular clinical symptoms were evaluated, and blood and conjunctival tissue were taken for analysis. Conjunctival tissue sections were stained with toluidine blue to visualize mast cell degranulation (MCD). Ovalbumin specific immunoglobulin E (OVA-s IgE), interferon-γ (IFN-γ), and interleukin-4 (IL-4) levels were determined in serum by enzyme linked immunosorbent assay. One-way analysis of variance was used for the comparison of data among the groups. results: Symptom scores were significant among all groups (F=38.72,
P<0.001). The symptom scores in Group B, were significantly higher than those in Group A (P<0.001).The symptom scores in each medication group were lower than those in Group B (P<0.05). There were significant differences in the mast cell among the six groups (F=15.28, P<0.001). The number of mast cell higher in Groups B-F than in the group A (all P<0.01). The serum levels of OVA-s IgE were significantly lower in Groups C-F than in the Group B (all P<0.05). The serum IFN-γ levels were significantly higher in Group A and Groups C-F than in Group B (all P<0.05). The serum IL-4 levels were significantly lower in Group A and Groups C-F than in Group B (all P<0.05). conclusions: In mice, sodium paeonolsilate eye drops have a therapeutic effect on experimental immunologic conjunctivitis initiated by OVA injection.It stabilizes mast cells and inhibits activated degranulation. Sodium paeonolsilate down regulated serum levels of OVA-s IgE and IL-4 while upregulating IFN-γ.